Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~ he present invention relates in general to a
speech synthesis system. In particular, the present inven-
tion relates to a device that produces a synthesis of
natural sounding speech that is usable in a conversational
mode. More specifically, the present invention generates
speech as a result of the manual input of an operator on an
input device that is coupled to an electronic signal gen-
erating device.
Since at least the year 1779, attempts have been
made to duplicate speech by artificial means. The early
machines utilized flexible resonators, usually shaped like
the human vocal tract and reeds to simulate the vocal cords.
At the 1939 World's Fair in ~ew York, the Bell Telephone
VODER (Voice Operated DEmonstratoR~ was exhibited. This
speaking machine had extremely complicated controls that
could only be operated by a person with a high degree of
skill who had been trained over a long period of time. The
machine utilized a pitch-defining current that was sent to a
vocal buzz generator above a certain level. ~elow that level,
a hiss was substituted. Currents were provided to a bank of
ten parallel audio filters used to define the strengths of
the signal inside the bandpass range of -that particular
filter. At tirnes, these filters had to be hoth turned on
and off within an extremely short period of tirne, such as
1/20th second and ripplecl in arpeggios that would be diffi-
cult for even a skilled pianist to duplicate. One version
of the VODER is disclosed in UO S. Patent No. 2,121,142.
Current efforts at speech synthesis are almost
unanimously directed toward electronic formation of intelli-
gible speech from a continuous flow of digital impulsesdelivered by a computer, or from a stored digital representa-
tion of a person's voice. In the latter case, inverse filter
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techni~ues are used to divide the speech waveforms into
signals to drive the synthesizer and reconstruct the voice
waveform. However, these approaches have not been used to
configure a speech-producing machine that can be continuously
controlled. In many applications, the human speech ls syn-
thesized by the generation and combination of a plurality of
sounds to represent basic speech parts, referred to as phonemes.
The phonemes are then strung to~ether to simulate words or
phrases. By analyzing the phonemes required for intelligible
speech, two major kinds of sounds were identified, namely
voiced sounds which are primarily the result of vibration of
the vocal cords resonating in the cavities that are formed,
along the voice -tract, and unvoiced sounds which are typically
the sibilants and which tend to be bas~cally derived from a
random sound source such as white noise. A plurality of sine-
wave generators of differing frequencies may also be used to
provide a selected number of basic waveforms representative
of the basic formants of sound. The waveforms are then com-
bined to produce a resultant, comple~ waveform. One such
synthesizer is disclosed in U.S. Patent No. 4,092,495. A
related approach is disclosed in U.S. Patent 4,163,120 whereby
stored speech waveforms representing basic functions are com-
bined with other waveforms instantaneously produced by means
of either time compression or time expansion of the stored
basic functions.
A number of prior art devices utilize stored repre-
sentations of operator selected words, phrases, phonemes and
morphemes. An input devlce is usually provided which utilizes
a keyboard having a plurality of individual touch sen~itive
locations, much in the manner of a typewriter. One .such device
is disclosed in U.S. Patent No. 4,215,240.
Currentl~, digital speech synthesizer integrated
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circuits are comrnercially available ~rom Texas Instruments
Inc., General Instrument, ~ational Semiconductor, A.M.I~ and
others. The Texas Instruments approach utilizes reflection
coefficient-type data to control the characteristics of a
digital filter. These devices are disclosed in a number of
United States Patents including Nos. ~,209,836, 4,304,965
and 4~328,395.
However, the recent synthesizers require either that
the phrase to be spoken must either be stored in a memory or
loaded into a register, thereby causing difficulty in real
time conversation. Furthermore, these modern devices do not
permit any individualistic input into the speech to permit
inflections, feeling, and emphasis. For example, without
using any fricative, plosive, or nasal consonants, a person
can say "Where are you?`'; but cannot say "W~ere are You?`' or
"Where are you?"~ Thus, although the prior art devices do
permit some form of communication, they are not readily appli-
cable in conversational cornmunications with individualized
characteristics.
The present invention overcomes the foregoing dis-
advantages of the prior art devices and permits feeling, inter-
pretation, inflections, and smoothness to be added to speech
sounds as they are being generated. The speech synthesizer
of the present invention can be played much in the manner
that a musical instrument can be played.
I'he present invention provides a means of inter-
active communication for voiceless people. The present
invention permits a feedback response Erom the user so that
continuous control over the desired response can be exercised.
In one em~odiment of the present invention, a playing surface
is utilized over which the fingers of the user can be moved
to command a two-dimensional control over the rnodeling of
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the vocal tract. This playing sur~ace can also utilize a
third variable determined by the amount o~ force on the play-
ing surface to control, for example, the pitch and/or in~lec-
tion of the voicing source. In this embodiment the two-dimen-
sional playing area causes the generation o~ vowels, dipthongs,
or semi-vowels (e.g. w, ~, r, 1). ~n additional selection
area is provided ~or the production of fricative or plosive
consonants.
In a prototype embodiment, the pitch o~ a voicing
buzz and the amplitude of the voicing buzz are controllable
as a single variable. The pitch/inflection variable is con-
trolled by the amount of pressure on the playing surface.
The formation of the sounds "played" on the input
device of the present invention can be done with a plurality
of analog circuits using operational amplifiers, or throu~h
the use of digital simulators that are commercially available.
In accordance with a particular embodiment of the
invention a speech sound generating system incl~des a means
for simulating the fre~uency response of the vocal tract,
the freauency response including two or more resonant peaks
or formants continuously movable in frequency. The operator
can then simultaneously and continuously control the fre-
quency locations of all the formants. Means are provided
for simulating electrically the fibration of the vocal cords
with variable pitch period and additional means continuously
responsive to operator input to control the vocal cord pitch
variation. The vocal cord simulation and the frequency res-
ponse simulation are combined to produce a resulting waveform
and transducing means cause the resulting wave~orm to be
emitted as an audible sound.
These and other features, objectives, and advan-
tages of the present invention will be set forth in or will
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be apparent from the detailed description of the presently
preferred embodiments disclosed hereinbelow.
FIGURE 1 is a perspective view of a first embodi-
ment of a manually operated, input board having a plurality
of consonant selection keys and a two-dimensional "playing
surface" for vowel selection;
FIGURF, 2 is a perspective view of a second embodi-
ment of an input board;
FIGURE 3 is a schematic, electrical block diagram
of an electronic circuit for decoding force and location
parameters produced by the input board depicted in Figure 2;
FIGURE 4 is an electrical schematic block diagram
for producing synthesized speech as a result of operator
produced myo-electric or neuro-electric voltages,
FIGURE 5 is an electrical schematic block diagram
of an embodiment of a speech synthesizer according to the
present invention;
FIGURE 6 is an electrical schematic block diagram
of another embodiment of a speech synthesizer in accordance
with the present invention;
FIGURES7a, 7b, and 7c are electrical schematic
diagrams depicting three embodiments oE a controllable
formant filter;
FIGURE 8 is an elect.rical schematic circuit diagram
of part of the synthesizer similar to the block diagram
circuit depicted in Figure 5 and depicting the voicing and
vocal tract filters;
FIGURE 9 is an electrical schematic circuit diagram
of the other part of the synthesizer similar to the block
diagram circuit depicted in Figure 5 and depicting the con-
sonant selection part of the circuit;
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FIGURE 10 is an electrical schematic block diagram
o~ a ~urther embodiment of a synthesizer utilizing a micro-
processor and a digital voice synthesizer,
FIGURE 11 is a cross-sectional view of one embodi-
ment of a two-dimensional position indicating tablet with
the dimensions exaggerated for clarity,
FIGURE 1~ is a plan view of the tablet of Figure 11,
with parts removed; and
FI~URE 13 is an electrical schematic circuit dia-
gram depicting the electrical connections to a tablet of
yet another embodiment.
Referring now to the figures in which like numerals
depict like elements throughout the several views, and in
particular with re~erence to Figure 1, there is depicted a
self-contained, portable speech synthesizer 20 comprised of
a housing 22 and an input board 24. Contained inside hous-
ing 22 and not depicted in Figure 1 is a power supply, such
as batteries, the electronic circuitry such as on a circuit
board, and a small speaker~
Input board 2~ includes a plurality of consonant
keys 26 through 38, a pitch/inflection control key 40, and a
playing surface 42. Keys 26 and 27 are marked '`m'` and "n'`,
respectively, and are for playing nasal consonants. Keys
29 through 32 are d~al-acting keys mounted transversely
about the center and playa~le by pressing on either side.
If the left side of these keys is depressed, a fricative
consonant will result and if the right side of these keys
is depressed the selected voiced fricative consonan-t will
be played. Keys 33 through 38 provide fricative or plosive
consonants. The surfaces of keys 26 through 38 have indicia
imprinted thereon taken from the standard International
Phonetics ~ssociation (IPA) characters.
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Playin~ surface 42 has a plurality of indicia
imprinted thereon from the standard IPA vowel symbols. Play-
ing surface 42, is preferably comprised of a flexible membrane
that is part of a playing tablet, described in greater detail
hereinbelow with reference to Figures 11, 12 and 13. The
particular locations of the consonant selection keys 26
through 38 and the particular location of the IPA vowel
symbols on playing surface 42 can be different than that de-
picted in Figure 1. The best locations are a function of
the ease of learning to play and the actual playin~ of syn-
thesizer 20. Pitch/inflection control key 40 is located so
that it can be operated by the thumb of either hand in much
the same sense that a space bar of a conventional typewriter
is operated.
Figure 2 depicts a second embodiment of a synthesize.r
20' that is substantially similar to synthesizer 20 depicted
in Figure 1. A major difference is that pitch/inflection
~ey 40 has been replaced by four force-sensing transducers
48, 50, 52, and 54 located beneath the four corners of play-
ing surface 42'. In synthesizer 20', playing surface 42' must
be relatively rigid such that the total force exerted thereon
can be conveyed thereby to transducers 48 through 54.
When finger pressure is exerted on playing ~urface
42 of either synthesizer 20 of Figure 1 or ,synthesizer 20'
of Figure 2, the corresponding synthesizer will emit a vowel
sound chosen at a pitch and intensity controlled by the total
amount of force,on pitch/inflection ~ey 40 or detected by
transducer's 48, 50, 52 and 54. For example, to produce a
dipthong, a continuous path is traced by finger pressure on
playing surface 42 from one vowel symbol to the next and, at
the same time, maintaining an appropriate pitch with control
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key 40 or by controlling the total force applied to trans-
ducers 48, 50, 52 and 54. As an example, to `'play" or sound
the word "you'`, an operator would trace a horizontal path
from the "i'` symbol, at location 56, to the symbol "u'`, at
location 58, the path of travel being indicated by arrow 60.
According to the standard IPA, the symbol "i" has the vowel
sound of '`ee" as in the word "bee`'. On the other hand, if
the exact reverse path is traced, the word "we" is produced.
As a further example, tracing the path from the symbcl "ae",
at location 62, to the symbol "i" at location 56, produces or
sounds the personal pronoun "I'`, which is a dipthong. As
another example, if a path is traced from location 58 ("u")
to location 62 ('`ae`') and then to location 56, ("i") the
synthesizer will produce the word "why". As a final example,
the sounds of the letter "r" and "1", known as laterals,
can be produced in the general vicinity of locations 64 and
66, respectively. ~lese laterals can be stressed as initial
consonants simply by a rapid motion from their respective
locations to the next vowel sound. Other words would be
obviously formed depending upon the particular path traced
by a finger of the operator on playing surface 42.
Force transducers 50, 52, 5~ and 56 depicted in
Figure 2 can be any one of a number of commercially available
devices. For example, they can be a variable resistance
transducer, such as short stroke linear potentiometers hav-
ing springs connected across the mechanical input such that
the output resistance (or voltage if connected as a potential
divider) is proportional to the force on the springs. In
addition, a direct current differential transformer (DCDT) or
a self-demodulating LVDT can be used. Other devices include
a transducer constructed of variable resistance materials
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such as a conducting foam positioned between two metallic
plates and having a lower electrical resistance in propor-
tion to the compressional fc)rce exerted on the metallic plates.
Alternatively, cells containing carbon plates or granules much
like those used in the early telephone transmitters can be
utilized. Finally, a semiconductor bending bearn transducer,
piezoelectric or piezoresistive bending beam elements (such
as those made by Gulton Labs of ~etuchen, NJ), or strain gauges
- in beams rings or bars arranged to measure their deflections
and hence the applied force. Other force transducers can be
used in the present invention ~hich would be obvious to
those of ordinary skill in the art.
The four transducers 48, 50, 52 and 54 utilized in
synthesizer 20' of Figure 2 can provide both the total arnount
of applied force on playing surface 42 and a resolution of
the force location in the x and y axes. An elec~rical cir-
cuit to accomplish this is depicted in Figure 3. The output
of transducers 48, 50, 52 and 54 are respectively arnplified in
instrumentation amplifiers 68, 70, 72 and 74. ~he inverses of
the respective voltages appearing at the output of instrumen-
tation amplifiers 68, 70, 72 and 74 are indicated respectively
as -F48, -F50~ F52 and -F54. The voltage oukputs from in-
strumentation amplifiers 68, 70, 72, and 74 are sumrned in a
summing operational arnplifier 76, the output voltage of which
represents the total applied ~orce, FT, applied on top of
playing surface 42. The output from surnming amplifier 76 is
provided to the Yl and Z2 inputs of conventional four-quadrant
integrated circuit multiplier-dividers 78 and 80. Summing
amplifier 76 can be a con~entional operational amplifier of
30 the 741, 747, or T~-074 type connecked as c~n inverting ampli-
fier with nominal unity gain (input resistance being equal
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to the feedback resistance). Instrumentation amplifiers, on
the other hand, should preferably have a precision and a high
gain with low drift, such as the operational amplifier LH0038
manufactured by National Semiconductor. Multiplier-dividers
78 and 80 are preferably of the type AD53~K or AD534L manu-
factured by the Analog Devices Corporation of Norwood,
Massachusetts. Multiplier-dividers 78 and 80 are connected
as percentage computers whereby the outputs are equal to a
scale factor, (which in the present embodiment is a full
scale of 10 volts), times the ratio of the inputs.
The output of instrumentation amplifiers 68 and
70 are also connected to and summed by a summing amplifier 82.
Similarly, the output from instrurnentation arrlplifier 70 is
summed with the output from instrumentation amplifier 72 by
a summing amplifier 84. Summing amplifiers 82 and 84 can be
identical to and identically connected as summing amplifier
76. The outputs from summing amplifiers 82 and 84 are res-
pectively connected to the Zl inputs of multiplier-dividers
78 and 80. The outputs from multiplier-dividers 78 and 80
are representative of coordinate locating signals that are
respectively proportional to the horizontal position, VH, on
a scale of, for example, 0 volts to 10 volts and to the verti-
cal position, Vv, on a scale of, for example, 0 volts to 10
volts. As menti.oned above, because of the connection of multi-
plier-dividers 78 and 80 as percentage computers, their res-
pective outputs are equal to the scale factor times the ratio
of total force minus the two selected forces divided by the
total force. Such an output is independent of the magnitude
of the force. The output VH of multiplier-divider 78 is near
0 when the force is applied on the line between transducers
48 and 50 (near location 56) and is near the scale factor when
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the force is applied on the right side, near location 58.
Similarly, the output signal Vv from multiplier-divider 80
is near 0 for forces applied at the top of playing surface 42
along a line drawn between transducers 50 and 52, and is near
the scale factor when the force is applied near the bottom
of playing surface 42 on a line between transducers 48 and 54.
The output signals VM and Vv are applied as control voltages
to tunable filters to adjust the formant positions in the
- vocal tract cireuitry of the synthesizer and the output signal
FT is applied to a voicing source eireuit to adjust the fre-
quency or pitch, diseussed hereinbelow.
Figure 4 depicts an alternate method of providing
input signals to a voice synthesizer. In this embodiment,
eonduetive piekup pads 102, 103, 104 and 105 are plaeed at
appropriate loeations on the skin of the operator. Piekup
pads 102 through 105 deteet eleetrieal signals produced by
the firing of muscles ~myo-electrie signals) or from the
firing of nerve axons or neurons (neuro-electric signals~.
These are the same signals whieh are reeorded in electro-
encephalograp~l,s. The piekup points on the user are determinedusing the eriteria of the best signal separation and the best
voluntarily eontrolled signals.
Piekup pads 102 through 105 are connected to the
inputs of an amplifier and filter circuit 106. Circuit 106
filters out the high frequéneies and provides amplified sig-
nals having frequeneies in the range of interest. The signals
from transdueers 102, 103, and 10~ roughly eorrespond to the
three output signals V~, Vv, and FT, in Figure 3, and are
identified as two formant control channels 108 and 110, and
to piteh/infleetion channel 112. The piteh/infleetion ehannel
112 drives a voieing generation eireuit 114 whieh in turn
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produces a voicing buzz that increases in pitch or repetition
frequency with an increasing output voltage from pitch/in-
flection channel 112. Voicing generation circuit 114 drives
a vocal tract circuit 116. Vocal tract circuit 116 includes
at least two tunable filters that are respectively controlled
by the output signals from formant channels 108 and 110 to
produce vowel-like sounds.
Pickup pad 105 is optional and is used to provide a
consonant control signal for the operator unable to make him-
self or herself understood by just using the vowel-like sounds
produced by vocal tract circuit 116~ Pickup pad 105, when
used, is connected through amplifier and filter cixcuit 106
to a consonant channel 118. Consonant channel 118, in its
simplest embodiment, can provide a plurality of consonants
based on a simplified voltage threshold detection circuit in
consonant circuit and mixer 120. Circuit 120 mixes the out-
put from consonant sounds produced therein with the output
from vocal tract circuit 116 and provides an output to an
amplifier 122, connected in turn, to a speaker 12~.
For example, the selection of a consonant.sound by
consonant channel 118 could be done on the basis of the voltage
threshold of the amplified signal from pickup pad 105. At
low voltage levels, no consonant sound is produced and the out-
put signal from the vocal tract circuit 116 is perm.itted to
go directly to amplifier 122. At a higher voltage level of
the amplified consonant control signal, a hissing sound could
be produced by consonant circuit 120 and mixed with the output
from vocal tract circuit 116. Such a hissing sound could
simulate the sound of the letters "s" or "f" in certain words.
At a still higher voltage level, consonant circuit and mixer
120 could produce a timed pause ~ollowed by a short plosive
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noise burst and mix it with the output signal from vocal tract
circuit 116. The timed pause and short plosive noise burst
would simulate the sound produced by the letters "g", "k", or
"p,~,d, or t." Although such a system is .a very crude method
of voice synthesis, it would still permit many extremely
handicapped persons to communicate a little.
With the above descriptions of Figures 1 through 4
as a basis, a more detailed discussion of a voice synthesizer
according to the present invention can now be undertaken with
reference to Figure 5. The operator inputs to voice synthe~
sizer 20 are schematically shown in boxes 150, 152, and 154
as a manual consonant selection, a manual force application,
and a manual position, respectively. The operator would apply
the manual consonant selection, using the synthesizer con-
figuration of Figure 1, to one of the consonant keys 26 through
38. The manual force application would be applied to pitch/
inflection control key 40 and the manual position would be the
x, y coordinates of a force applied to playing surface 42. The
particular consonant key selected, as discussed above, will
be either a fricative or plosive, voiced or unvoiced consonant.
This is schematically shown in Figure 5 by a four quadrant
consonant key panel 156. Consonant key panel 156 does not
depict nasal consonant keys 26 and 27 in order to maintain
simplicity in the circuit. These consonant keys are, however,
depicted in the detailed electrical schematic circuit depicted
in Figure 8 and discussed below. As discussed below, nasal
consonant keys 21 and 22 operate directly on the formant
filters.
The amount of force applied is detected in the voicing
30 pitch and inflection circuit 158. Circuit 158 generates a
voicing waveform or buzz having a .substantially constant
amplitude and a frequency that varies proportionally to the
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magnitude o~ the force applied. Circuit 158 incorporates
time constants to a.llow the frequency to decrease smoothly to
a near-zero, non-oscillating condition upon the removal of all
input force. In the preferred embodiment of circuit 158, the
circuit also includes means to detect a predetermined, minimum
amount of force before permitting the frequency of the wave-
form to be increased above its near-zero, non-oscillating
condition.
The rnanual position input indicated at box 15~ is
applied to a position resolution circuit 160. Position resolu-
tion circuit 160 provides two outputs 162 and 164, correspond-
ing for example, to the X coordinate and the ~ coordinate on
playing surface 42 in Figure 1. Such a circuit, on the ot~er
hand, could be that depicted in Figure 3, which circuit would
be used in conjunction with the synthesizer 20~ depicted in
Figure 2. Outputs 162 and 164 from circuit 160 are respectively
coupled to the control inputs of a tunable formant filter 166
and a second tunable formant filter 168. me signal input to
tunable ~orm~nt filter 166 is provided by the signal generated
by voicing pitch and inflection circuit 158, described herein-
above. The signal input to second tunable formant filter 168
is provided by the output of tunable formant filter 166~
Formant filters 166 and 168 preferably have narrow
bandpass characteristics similar to the resonances of the
human vocal tract from the vocal cords to the constriction
formed by the hump of the tongue (formant filter 168), and
similar to the re~30nances of the human vocal tract from the
hump of the tongue to the front of the mouth (formant filter
166~. Other properties of these filters can i~clude the
ability to transmit frequencies outside the bandpass range
in an attenuated magnitude, and some fixed filtering to model
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other non-tunable resonances. The location of the adjustable
center ~requencies of the bandpass filters (i~e., the tuning
of the filters) is continuously variable by the control input
signals generated by position resolution circuit 160. q'he
feature of having continuously variable center ~requencies of
the formant filters, especially during the pronunciation of
vowel sounds, imparts a natural and smooth sound, similax to
normal speech, and is somewhat analogous to the muscles of
the mouth and throat almost always being in motion while
speaking is occurring.
As mentioned above, the output of tunable formant
filter 166 provides the input signal for tunable formant
filter 16~3. This arrangement is known as a series or cascade
filter. However, a paralle'l filtér could also be utilized
simply by having the output from voicing pitch and inflec-
tion circuit 158 providing the signal input to both formant
filters 166 and 168 in parallel.
The output from tunable formant filter 166 is also
provided to a consonant control and mixing circuit 170. The
output from second tunable formant filter 168 is also coupled
to the input of mixer 170. A third input to mixer 170 is
derived from the selected consonant.
The consonant selected in key panel 156 has a corres-
ponding noise waveform generated in a pseudorandom consonant
noise generator 172. Noise generator 172 can be a commercially
available circuit that is comprised of a shift register having
20 to 45 stages, with about 3 exclusive -OR gates at selected
locations and a means for determining the polarity of a signal
to be shifted into the input by comparing the even or odd count
of the bits at the 3 sample locations. The result is a long
binary number having from 1000 to 2000 bits with the l's and 0's
occurring randomly, but repeating as the resultant number
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recirculates in the shift registers to form a bit stream.
When the bit stream iS passed through an audio amplifier, the
result i3 the hissing sound of white noise~
The consonant sounds are implemented by inserting the
filtered white noise into mixer 170. Unvoiced fricative con-
sonants can be sounded continuously, as long as their respec-
tive contacts of switches 28 through 32 of Figure 1, for
example, are held closed. However, vowel sounds must be
suspended while unvoiced fricative consonants are being spoken
in order to simulate actual speech. This is accomplished by
interrupting the contributions from filters 166 and 168 in
the consonant control and mixing circuit 170. In Figure 1,
the unvoiced fricative consonants appear on the left-hand
side of keys 28 through 32. For example, the unvoiced frica-
tive consonant of key 29 is the "th`' as in the word "theatre"
and the fricative consonant of key 31 is the "sh" as in the
word "she".
Voiced fricative consonants appear on the right-hand
side of keys 28 through 32 and are treated in a similar way
as the fricative consonants, except that the consonant noise
is used to modulate the voicing waveform. Exemplary voiced
fricatives are the r~ght-hand side of key 31 which represents
the letter '`~" as in the word "azure", and the letter "z" on
the right-hand side of key 32 as used in the word "zoo".
The clock fre~uency determining the shift rate of
noise generator 172 is selected according to the range of
frequencies contained in the respective consonant. For
example, the consonant "h" has the lowest clock frequency,
the consonant '`e`' has a relatively high clock frequency, and
the consonants "f`' and "s" have an intermediate clock frequency.
If the consonant is voiced, the voicing waveform is modulated
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by the output of noise generator 172, as indicated schematic-
ally by switch 174.
The output from noise generator 172 is coupled to the
input of a tunable consonant filter 176. Consonant filter 176
further modifies the fre~uency content of the signal by passing
the signal through a bandpass filter, the center frequency of
which can be set at an appropriate value for the selected con-
sonant. For example, the consonant "h" has a low center
frequency because it is formed in the back of the mouth cavity.
On the other hand, the consonant "s" has a high center fre-
quency since it is formed between the teeth and the lips.
As mentioned above, the output of consonant fil-ter
176 is fed to an input of consonant control and mixing circuit
170. Circuit 170 includes a means to control the timing of
plosi~e consonants (unvoiced plosives t, k, and p as represent-
ed by keys 33 through 35 in Figure l; and voiced plosives d, g,
and b as represented by keys 36 through 38 in Figure 1). Plos-
ive consonants are characterized by a stop in the flow of
sound while the air pressure is being built up. The built up
air pressure is then released in a short burst of sound. While
the key switch contact for a plosive consonant is held down,
the sound is interrupted and the short burst of sound is timed
by timers once the key i9 released. Timers must be used since
the time duration is too short to be controlled accurately
by the corresponding key switch.
Mixer 170 sums all of the inputs thereto and pro-
vides the summed signal at the output thereof. The output of
mixer 170 is coupled to a small speaker 178 through a conven-
tional audio arnplifier 180. An exemplary audio amplifier
would have a power rating of about 100 milliwatts to 1 watt.
A power supply 182 for synthesizer circuit 21 is
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shown schematically with a plus voltage and ground outputs.
Preferably, power supply 182 is comprised of batteries.
~ ith reference now to Figure 6, an electrical block
diagram of a synthesizer circuit 21t is depicted that is
similar to, but more detailed than, the electrical block
diagram of a synthesizer circuit 21. Synthesizer circuit
21~ also incorporates a nasal consonant selection circuit
200 coupled to a fi~ed filter 202 that is connected between
tunable formant filter 166 and a second tunable forma~t-filter
204. The output of second tunable formant filter 204 is
coupled to the signal input of third tunable formant filter
168, whose output is now also connected to the signal input
of a fourth tunable formant filter 206. The control signal
for second and fourth formant filters 204 and 206 is respect-
ively provided by a first function generator 208 and a second
function generator 210, the inputs of which are both coupled
to the outputs of position resolution circuit 160. Stored
information in function generators 208 and 210 provides the
tuning or control signals for third and fourth foxmant filters
204 and 206.
Thus, when the first two formants are determined by
the output of position resolution circuit 160, two additional
formants are created which help augment and refine the simula-
tion of the vowel formation. Function generators 208 and 210
can be implemented with a digital storage means, retrieved as
a function of two digital addresses derived from the output
signals of position resolution circuit 160 by an analog-to-
digital conversion, or may be extensions of conventional, well-
known variable slope function generators having diode isolation
between adjustable segments. Such function generators are
normally single variable inputs, single outputs. However,
- 18 -
9~7~
simple algorithms can be incorporated by having a second
input modify the slopes or break points, or multiply the
analog output signal. Also, the outputs of two of the single-
variable filters can be multiplied.
Fixed filter 202 adds a simulation of the nasal
resonances of the head cavity and sinuses. When the nasal
consonants, such as keys 26 and 27 of Figure 1, are selected,
the characteristics of fixed filter 202 are changed in the
circuit so as to simulate a nasal sound.
Outputs from all of the filters, namely tunable
formant filters 166, 168, 20~ and 206, and fixed filter 202,
are all coupled to the mixer of circuit l?o and are mixed
together with the output from consonant filter 176. The
particular order of the various filters can be varied from
that depicted in Figure 6 so as to improve certain speech
synthesization, as would be obvious to one of ordinary skill
in the art.
Three different embodiments of tunable formant or
consonant filters are depicted in Figures 7a, 7b, and 7c.
The various R-C values are selected to place the nominal fre-
quency range of the filter in a desirable, predetermined range.
In Figure 7a, the tunable filter control signal is
provided by the output of a joy stick controller when the joy
stick is moved, for example, in the upward direction. The
motion of the joy stick (not shown) is resolved into the
rotation of potentiometer 302. The lower the resistance of
potentiometer 302, the higher will be the frequency produced
by the filter.
The basic filter cixcuit is comprised of three opera-
tional amplifiers 304, 306, and 308 connected in a loop. This
circuit is similar to the circuit used to generate sine and
cosine signals in analog computers. Such a circuit is comprised
_ ~ g _
2~g~
of two operational amplifiers connected as integrators and
one operational amplifier connected as aIl inverting amplifier.
In the circuit of Figure 7a, amplifiers 30~ and 308 are con-
nected as integrators and amplifier 306 is connected as an
inverting amplifierO
The oscillation of the circuit is begun with an
initial voltage on one of the integrator capacitors. Once
started, an input is not necessary since the circuit oscillates
at a constant amplitude. However, by adding damping or dissi-
pation to a single frequency circuit, such as that provided
by resistors 310, 312, and 314, the oscillations die out and
other frequencies near the center frequency are transmitted
with attenuation~ An input signal is applied at resistor 316
and can drive the circuit. The output of the circuit is taken
at point 318 located at the output of operational amplifier
306O
The loop gain of the filter circuit depicted in
Figure 7a varies according to the ratio of the resistance of
resistor 320 divided by the sum of the resistances of resistors
20 322 and 302. The loop gain also sets the center frequency of
the circuit. Resistor 322 prevents division ~y zero (which
results in howling). ~le tuning range of the circuit depicted
in Figure 7a is a maximum of 50:1 in fre~uency with t~e values
of resistors 322 and 302 being 1.8 kiloohms and 100 kiloohms
adjustable, respectively. The filter input and the loop feed-
back from amplifier 308 are added through two identical, high
resistance resistors 316 and 324, respectively.
Operational amplifier 304 has an R-C series combina-
tion as a feedback which tends to give increasing damping at
fre~uencies higher than the center frequency. The output from
operational amplifier 304 is amplified and inverted by ampli-
fier 306. The amplified signal from amplifier 306 is not only
- 20 -
~9~o~
ta~en as the filter output at 318, but is also fed to the input
of operational amplifier 308 through an input resistor 326.
Operational amplifier 308 has an R-C parallel combination in
its feedback circuit which tends to give increasing damping
at frequencies lower than the center frequency. Although the
feedback circuit around operational amplifier 308 need only
consist of a single capacitor and a single resistor in parallel,
the feedback circuit depicted around operational amplifier 308
is more complicated so as to give a somewhat broader band-
width formant with less annoying ringing.
The formant filter depicted in Figure 7a is prefer-
ably used as second tunable formant filter 168. Preferably,
tunable foxmant filter 166 and tunable consonant filter 176
utilize only a parallel R-C feedback around operational ampli-
fier 308.
Other devices can be substituted in the circuitry of
the tunable formant filters once it is realized that the con-
trol of the filter comprises changing the gain from the output
of amplifier 304 to the input of amplifier 308. Voltage con-
trol of the gain is provided for in Figure 7b and digitalcontrol of the gain is provided for in Figure 7c.
With respect to Figure 7b, inverting amplifier 306
of Figure 7a has been replaced by a four-quadrant analog
multiplier-divider 352 configured as a divider so that the
output center frequency is proportional to the reciprocal
of the control voltage supplied at the input 354. An adjust-
able potential divider, comprised of potentiometer 356 and
resistors 358 and 360, is provided at the inverting X-input
of multiplier-divider 352 so that division by zero cannot
occur if the control voltage at input 354 goes to zeroO Multi-
plier-divider 352 is preferably of a type similar to Analog
Devices AD534.
- 21 -
: ~.
~L2q~9~70~
Alternatively, the gain of the circuit depicted in
Figure 7b can be set by configuring multiplier-divider 352
as a multiplier. However, this would change the locations
of the vowel formants on playing surface 42 (Figure 1).
The vow~l formants would be crowded to one edge and th~re
would be poor resolution between the different IPA symbols
if the tuning voltage varied linearly and controlled the gain
multiplicatively. A simple and inexpensive device to control
the gain as a function of the bias current in a circuit con-
figured as a multiplier, is operational amplifier CA3060, athree operational transconductance amplifier array manufac-
tured by RCA. Since the control voltage of 10 volts at input
354 produces a unity gain in multiplier-divider 352, the resis-
tance of resistor 326' has been increased to 22 kiloohms from
the 10 kiloohm resistance used for resistor 326 in Figure 7a.
In Figure 7c, a twelve-bit multiplying digital-to-
analog converter 376 is used to digitally set the input and
feedback resistors for operational amplifier 306. Such a con-
verter could be commercially available typa AD7541 manufac-tured
by Analog Devices. An èight-bit device can also be used, but
a resolution of 256 different center frequencies would be pro-
vided instead of ~096 different center frequencies provided by
a twelve-bit converter. Converter 376 is configured as a
divider, so that the gain is inversely proportional to the
value of the digital word. Alternatively, digital multiplica-
tion of the gain could be employed. Since the gain of con-
verter 376 with all bits ON is (Minus) unity, the value of
resistor 326' has been changed from 10 kiloohms of resistor
326 in Figure 7a to 22 k1loohms in Figure 7c.
With reference now to Figures 8 and 9, a detailed,
schematic electrical circuit diagram is depicted of a speech
synthesizer according to the present invention. In this
- 22 -
~IIL2~9'7~
embodiment, the manual position information is obtained from
the mechanical resolution of the handle position of a joy
stick control (not shown~. The rotational angle of the joy
stick position is resolved by two 100 kiloohm potentiometers
402 and 404, depicted schematicall~ in Figure 8. Potentio-
meter 402 responds to vertical motions of the joy stick ~not
shown) and is electrically located in the circuitry of tunable
formant filter 166 (Figure 6). Potentiometer 404 responds to
the horizontal motions of the joy stick control and is elec-
trically connected in the circuitry of second tunable formantfilter 168. Thus, in this embodiment of the invention, the
position resolution circuit 160 of Figure 5 has been replaced
by a mechanical resolution of the input.
In a similar manner, the pitch/inflection control
key 40, and the '`m" and "n" nasal consonant keys 26 and 27 have
been replaced by specially designed, pressure-sensitive resis-
tance switches 406, 408 and 410, respectively. This switch
(not shown) comprises a spring metallic conductor strip mounted
on a block of carbon-impregnated foam. This foam is commerc-
ially available and can simply be of the same type as is used
for shipping integrated circuit chips. Circuit pins integral
with the metallic conductor penetrate into the foam to connect
the conductor to the foam. A second metallic strip is located
on the opposite side of the foam block, and the two strips form
the two switch terminals. An exemplary size of the foam block
is 2 x 3 x 0.5 cm. The xesistance between the two strips be-
gins at essentially infinity (open circuit) and is reduced to
about 50,000 ohms at the first light contact. The resistance
decreases with increasing force, down to a lower useful value
30 of about 1,000 ohms. Pitch/inflection switch 406 has a func-
tion and produces a result similar to the expression pedal of
an organ. Such a switch provides clickless switching.
_ 23 -
~2~70~
The circuit depicted in Figure 8 will now be des-
cribed. Pitch/i~flection switch 406 is connected between a
negative 15 volt power supply and the inputs of two operation-
al amplifiers 412 and 414. The negative output voltage of
switch 406 is denoted VVN (Voicing Voltage ~egative). A
capacitor 416 connected around pitch/inflection switch 406
smooths the VVN signal so that it changes in a stepless fashion.
The output from pitch/inflection switch 406 is drained to +15
volts through a resistor 418 when pitch/inflection switch 406
is not being operated so as to assure that the VVN signal
goes to zero volts. Operational amplifier 412 is connected
in the circuit as an inverter and produces a positive W P
output signal. Operational amplifier 414 is connected as an
integrator as a result of a feedback capacitor 420. A diode
422 in the feedback circuit of opera-tional amplifier 414
prevents the output thereof from going negative. In addi-
tion to a resistor 424 connected to the output of pitch/
in~lection switch 406, four other inputs are provided to
operational amplifier 414 through resistors 426, 428, 430,
20 and 432. The input to operational amplifier 414 through resis-
tor 432 is connected to a monostable, multivibrator or one-
shot 434. One-shot 434, when it is conducting, turns opera-
tional amplifier 414 off during which time diode 422 clamps
the output voltage thereof to a slight negative value (-.6
volts)J When operational amplifier 414 is not being held
in a non-conducting condition, the output voltage from it
changes linearly with time whenever there is a constant im-
balance of the currents through resistors 426, 428, 430 and
432 at its input.
One output from operational amplifier 414 is con-
nected through voltage dividing resistors 436 and 437 to
trigger a second monostable multivibrator or one-shot 438.
~ 24
~2~
One-shot 438 is set to provide a 0.3 ms pulse at its Q output
as determined by timing capacitor and resistor 440 and 442,
respectively. rrhe Q output from one-shot 438 is coupled
through two voltage dropping diodes 444 to the input of opera-
tional amplifier 414 through resistor 426. The output from
one-shot 438 is clamped at the voltage of WP less the voltage
drop through diodes 444 by the action of a third diode 446
connected to the output of operational amplifier 412. m e
output current from one-shot 438 through resistor 426 will
almost balance the negative current from the VV~ signal applied
through resistor 424.
rrhe output from operational amplifier 414 is also
applied to the non-inverting input of a comparator operational
amplifier 448. The output of comparator 448, which is the same
polarity as the input, is connected through a resistor 450 and
a diode 452 to the input of operational amplifier 414 through
resistor 428~ Comparator 448 is provided with a hysteresis as
a result of feedback resistor 454 and input resistor 456 con-
nected together as a voltage divider.
The output from operational amplifier 414 is also
connected to two voltage divider networks comprised, respect-
ively, of resistors 458 and 459 and resistors 460 and 461. The
output from the voltage divider network formed by resistors 458
and 459 is a signal denoted VMODIN. T~e VMODIN signal is
coupled to noise generator 172 to be modulated thereby when
voiced consonants are being formed. rrhis is described in
greater detail hereinbelow with reference to Figure 9. The
output from the voltage dividing network comprised of resis-
tors 460 and 461 is connected into the signal input of tunable
formant filter 166. rrhe voltage of the signal input to formant
filter 166 is approximately l/lOOth of the output of operational
amplifier 414. For~ant filter 166 is comprised of operational
- 25 -
~g~
amplifiers 462, 463 and 464. The operation of formant
filter 166 and the connection of its elements are essen-
tially the same as mentioned above with respect to the
modificatlon of Figure 7a. The gain of ~ormant filter 166
is highest when the joy stick handle is positioned farthest
to the left, causing potentiometer 402 to have a minimum
resistance. ~he center frequency o~ formant filter 166
is selected so as to be higher than the center frequency
of formant filter 168. As mentioned above, the simple
parallel combination of a capacitor 465 and resistor 466
in the feedback of operational amplifier 464 results in a
slightly narrower bandwidth. The output from formant filter
166 is connected to the input of a fixed filter 202 that in-
cludes an operational amplifier 468 connected as a non-
inverting follower having a gain and a bridged "T`' filter in
its feedback path. The nominal gain is determined by the
ratio of the resistances of feedback resistor 470 and resistor
472 connected between ground and the feedback input to the in-
verting input of operational amplifier 468. The bridged "T"
filter is comprised of capacitors 473 and 474 and a resistor
475 connected therebetween in parallel combination with resis-
tors 479 and 480 and capacitors 481 and 478~. Because the
bridged "T" filter components are not selected for a true
null balance at a given frequency, and resistor 470 shunts
the "T" filter, the bandwidth provided by fixed filter 202
is quite broad. The values of the components of fixed filter
202 are selected based on the output of a satisfying sound
and can be varied to produce a different sound.
As mentioned above, "m" switch 408 and Un~ switch
410 are connected so as to affect the filtering of fixed
filter 202. The "m" switch 408 is also connected around opera-
tional amplifier 463 in combination with output resistor 476
- 26 -
~ g~
and the shunted pair of a resistor 477 and a capacitor 478.
On the other hand, `'n" switch 410 is connected to shunt the
output from operational amplifier 463 and resistor 476 to
ground through capacitor 478'. This has the effect of atten-
uating the higher frequencies being fed into operational
amplifier 468. Also connected into the feedback path of
operational amplifier 468, and effective upon the operation
of "n" switch 410, is a further filter comprised of resistors
479 and 480 and a capacitor 481 connected between the two
resistors and between the output of "n" switch 410 and
capacitor 478'. Consequentl~ a slight amount of regenera-
tion is provided b~ the capacitor divider formed from capac-
itors 478' and 481 back into the non-inverting input of
amplifier 468. This causes an increased nasal tone due to the
selective fre~uency amplification under positive feedback.
The output from fixed filter 202 is sent both to
mixer 170 and to the input of second formant filter 168 through
resistors 482 and 483. Filter 168 is identical to the filter
depicted in Figure 7a and described above. A capacitor 484
connected between ground and the junction of resistors 482
and 483 provides a 6 dB per octave roll-off to frequencies
above 2,000 Hz to attenuate noise and other frequencies too
high for the formant filter 168. A CMOS gate 485 is connected
in parallel with capacitor 484 between ground and the ~unction
of resistors ~82 and 483. CMOS gate 485 is operated by a
signal VSTOP to shunt the input signal to formant filter 168
to ground when VSTOP signal is non-zero. ~his condition occurs
during voiced and unvoiced consonants and during the silent
period preceding voiced plosive consonants. Thus CMOS gate 485
supplies some of the consonant control functions of block 170
depicted in Figures 5 and 6.
The outputs from filters 166 and 168, from a consonant
- - 27 -
-` ~2¢970~L
filter 176 (described below with respect to Figure 9), and
~rom fixed filter 202 are coupled to mixer 170 through corres-
ponding resistors 486 through 489,respectively. An opera-
tional amplifier 490 having feedback comprised of a resistor
491 and a capacitor 492 connected in parallel sums the inputs
and provides an output to a conventional, power operational
amplifier 493, which in turn, drives a speaker 494. A capaci-
tor 495, connected between the output from tunable formant
filter 166 and input resistor 486 to mixer 170, is shunted to
ground and provides noise suppression and a 47 kHz break point.
The feedback combination of resistor 491 and capacitor 492
provides a 6 db per octave attenuation for frequencies above
15.9 kHz.
The remainder of the synthesizer electronic circuit
is depicted in Figure 9. This circuit senses whether any one
of consonant keys 28 through 38 have been operated and also
generates the signal CONSONANT, which is connected directly
to mixer 170 as mentioned above. This circuit also provides two
output signals, VOICE and VS~0~, both used to mute some or all
of the voicing waveforrns generated in Figure 8. The circuit in
Figure 9 receives as an input, the signal VMODIN, which is then
noise modulated to forrn voiced frica~ives and plosives. With
the exception of the power supplied to the four operational
amplifiers in the circuit o~ Figure 9, all of the power
supplied is ~5 volts DC.
Keys 28 through 3~ can be conventional switches, or
can be comprised of metallic areas formed on an insul~tin~
substrate of a printed circuit board. Depression of the
appropriate key provides contact between a corresponding mem-
3~ brane, denoted 502 and 504 in Figure 9 and the metallic area.
l~embrane 502 is connected to the signal PL. Membrane 50~ is
connected to ground and supplies this input through the
- 28 _
~2~7~1
appropriately depressed key and through a debounce circuit.
As mentioned above, keys 2~ through 32 are double~acting keys.
A further membrane 506, located on each key for electrical
contact with membrane 502 when the right side of the key is
depressed, is electrically`connected through a further de-
bounce circuit to generate the signal VF. However, membrane
506 is left floating when the left side of the ~ey (for
unvoiced fricatives) is depressed. Thus, depression of the
right side of keys 28 through 32 generates two si~nals whereas
the depression of the left side thereof generates only a single
signal.
The debounce circuits are formed by two CMOS invert-
ing amplifiers connected in series, two resistors connected in
series between plus voltage and the contact pad of the corres-
ponding key, and a capacitor connected between the output of
the second inverting amplifier and the junction between the
t~o resistors. Positive feedback occurs when the correspond-
ing key is depressed and partially grounded. The output of
the second inverting amplifier snaps from its plus voltage to
ground, driving the resistor tie point downward through the
capacitor. This removes the ability of the contact pad to
become positive again and thereby cancels any possibility of
a bounce. When the resistor tie point has stabilized at about
half the positive voltage and the key is released, the second
amplifier output flips from zero voltage to the positive
voltage, tending to make the amplifier input become positive
rapidly, thereby assuring a clean transition. The first
amplifier will then go to zero, signifying an open switch.
The two resistors have a value of 1 megohm and the capacitor
has a value of .1 microfarads.
The outputs from all of the debounce circuits corres-
ponding to ke~s 28 through 32 are all ORed together with an
-- 2g --
~ ~2~)9~0~
OR gate 508 and are individually connected to two correspond-
ing CMOS switches in resistor banks 510 and 511. The outputs
from the corresponding debounce circuits to keys 33 through 38
are all ORed together in an OR gate 512 and are individually
connected to the input of a corresponding monostable multi-
vibrator or one-shot 513 through 518. The output from OR
gate 512 is connected through an OR gate 520 to membranes 502
of fricative consonant keys 28 through 32~ This applies a
high voltage to those pads and prevents any signal f~om being
generated thereby. This is necessary because many consonant
sounds in the English language are double, such as the "ch"
in the word cheese, or the "j" in the word judge, which are
actually formed b~ the tS and d 3 . It would be difficult to
time the finger movements of an operator if the second con-
sonant sound were not interrupted by the first. When membrane
502 is not high, OR gate 520 provides a ground signal thereto,
which can then be conveyed through an appropriately depressed
key to generate a high signal in t~e corresponding debounce
circuit.
The duration of the pulse produced by one-shots 513
through 518 for the consonant corresponding to keys 33 through
38 is individually set through a corresponding capacitor and
resistor. The duration of each one-shot will depend upon tha
particular, corresponding consonant and can be individually
set for maximum intelligibility. In general, consonants '`t",
"k", and "p" have longer times (on the order of 100 milliseconds~
than do the consonants "d", "g", and "b'` (which are on the order
of 40 milliseconds). Exemplary values of the capacitors for
each of one-shots 513 through 518 are one microfarad and exem-
plary values for the resistors of one-shots 513 throuyh 515
are 330 kiloohms and for one-shots 516 through 518 are 150
kiloohms.
- 30 -
.~ ~.
~2~
The output from one-shots 513 through 518 are ORed
through an OR gate 522. In addition, pairs of one-shots 513
and 516, 514 and 517, and 515 and 518, also have their Q
outputs ORed together in OR gates 524, 525, and 526, respect-
ively. The outputs ~rom these OR gates are connected to
corresponding CMOS switches in resistor banks 510 and 511.
The output from OR gate 522 is connected to the N input of a
one-shot 528 and to membranes 502 through OR gate 520. The
output rrom OR gate 522 is also connected to one input of
another OR gate 530, the other input of which is provided
by the output from OR gate 508. The output from OR gate 530
is inverted and connected to the inhibit pin of a conven-
tional, complex sound generator 532, such as integrated circuit
SN 76477.
One-shot 528 is connected to one input of an OR
gate 534, the other input of which is provided by the output
of OR gate 520~ The output ~rom OR gate 534 is ORed in an OR
gate 536 with the output from OR gate 508 and provides the
signal VSTOP used to inhibit the production of vowel sounds
as discussed above with respect to Figure 8. One-shot 528
has its associated capacitor and resistor selected so as to
provide an additional silence of about 25 milliseconds. This
can be accomplished with a capacitor having .33 micro~arads
and a resistor having 220 kiloohms. Thus, vowel sounds are
inhibited (VSTOP high) during the time: 1) any plosive key is
depressed ~PKEY high), 2) any unvoiced timer is active (PUVT
high), 3) any voiced timer is active (PVT high); or 4) one-
shot timer 528 is active. The signal leaving OR gate 534 is
called YSTOP and the signal leaving OR gate 508 is called FR.
While any voiced timer i~ active ~i.e., PVT is high), the MOD
signal is low, allowing an AND gate 538, which is also connect-
ed at one input to the output of OR gate 536, to remove the
- 31 _
7~i~
inhibi-t on the VOICE signal line, and enabling a modulator
540 that is comprised of a transistor 542 and an OR gate 543.
The other input to OR gate 543, which is the modulated signal,
is the NOISE output from sound generator 532.
As mentioned above, modul~tor 5~0 is enabled and
.AND gate 538 is disabled whenever MOD signal is low. This
occurs whenever one of the inputs to an OR gate 545 is high,
the output being inverted by an inverted 546. OR gate 545 is
- active whenever signal VF is produced (iOe. whenever the right
side of keys 29 through 32 are depressed), or whenever there
is an output from one-shots 516, 517 or 518 (i.e. following
the depression of one of keys 36, 37 or 38). In addition, MOD
signal opens CMOS switch 548. This results in an interruption
of the noise input from sound generator 532 to the input of
consonant filter 176. However, noise output from sound
generator 532 can now drive modulator 540 (since OR gate 543
is unclamped) to alternately clamp and unclamp the voltage
VMODI~ to ground, thereby modulating this signal and sending
the modulated signal to consonant filter 176 instead of the
unmodulated signal.
Sound generator 532 has a noise source clock rate
that is controlled by the amount of current through pin 4.
This current is determined by resistor 550 of resistor bank 510
in parallel combination with any other one of the selected
resistors. Except for resistor 550, each of the resistors of
resistor bank 510 is tied parallel with resistor 550 by a CMOS
switch. As mentioned above, these switches are controlled by
the outputs from the various debounce circuits. Resistor bank
510 is located between the output of operational amplifier 552
connected as a follower amplifier and the clock input of sound
generator 532. T~e output signal of follower amplifier 552 is
slightly positive whenever VVN is 0 (i.e. no operation of
- 32 -
; ~2~g~
pitch/inflection control key 40). The output of follower amp
552 goes negative as si~nal VVN goes negative and this results
in some pi.tch control of the consonant sound. Suggestive
resistances in kiloohms of the resistors in resistor bank 510,
beginning with unswitched resistor 550 are as follows: 330, 10,
39, 150, 82; 120, 47; and 27.
As mentioned above, the signals that switch the
resistors in resistor bank 510 simultaneously switch the resis-
tors in resistor bank 511. These resistors are connected in
the input to the inverting operational amplifier of consonant
filter 17~ (denoted 306 because of the similarity to the
.filters described herein a~ove.with respect to Figure 7).
The amount of resistance switched into consonant filter 176
sets the gain of the inverting operational amplifier resulting
in a high gain for a high formant frequency. Suggestive resis-
tances in kiloohms for the resistors of resistor bank 511,
~eginning with the resistor on the left side as seen.in
Figure 9 are as follows: 47; 150; 82; 120; 2~0; 39; and 100.
The operation of the synthesizer as depicted in
Figures 8 and 9 is as followsO Depression of pitch/inflection
switch 406 smoothly generates negative voicing voltage VVN which
flows through resistors 423 and 424 in parallel into the in-
puts to operational amplifiers 412 and 414~ ~he flow of nega-
tive current into operational amplifier 414 sets the slope of
the positive ramp of the voicing signal voltage which is gen-
erated at the output thereof~ The more negative VVN is, the
steeper is the slope of the voicing signal voltage (sometimes
called the glottal pulse) at the output of operational ampli-
fier 414. This results in a more rapid rate of change in the
frequency or pitch of the voicing signalO When the consonant
circuits are active, a 5 volt level called VOICE is applied to
resistor 430 tending to stop all oscillationsO Diode 422 con-
ducts at this time.
- 33 _
970~
Assuming that one-shot 434 has just turned off (i.e.
the Q output is 03, the output of operational amplifier 414
will begin to rise from its diode-clamped slight negative
output voltage of -0.6 volts. For a 10,000 ohm value for
pitch/inflection switch 406, the voltage out of operational
amplifier 414 will climb 3.8 volts in 1.7 milliseconds. At
this point, there will be a sufficient input to trigger one-
shot 438 to provide a .3 millisecon~ pulse at the Q output.
The current out of one-shot 438 flows through an output
resistor into diode 446, which will allow the voltage at the
top of a clamping resistor at the output of diodes 444 to go
no higher than voltage of the VVP signal (actually slightly
lower than W P voltage because of the voltage drop of diodes
444). The input positive current to operational amplifier 414
through resistor 426 will almost balance the negative current
coming through resistor 424 from the VVN signal. This produces
a momentary halt or plateau in the voltage wave form out of
operational amplifier 414 for 0.3 millisecond, until one-shot
438 times out. Then the voltage continues to climb at the
same slope for another 1.7 milliseconds until the voltage
reaches 8.0 volts to trigger comparator 448. The plateau in
the wave form contributes a slight rasp or faint rattle to the
voicing wave form and thereby contributes to its naturalness.
The output of comparator 448 goes positive and by means of the
current flowing through resistor 450 clamps the voltage at the
output of diode 452 to the VVP voltage. This results in a
positive current flowing into operational amplifier 414 that
is more than five times greater than the current flowing
through resistor 424 as a result of resistor 428 being approxi-
30 mately 1/5 the resistance of resistor 424. The algebraic
dirference of 4 times the positive current resets the output
voltage of operational amplifier 414 to zero in a very short
- 34 -
~z~ o~
time (about 1 millisecond). Comparator 448 also resets (goes
very negative toward -15 volts) as the output voltage of
operational amplifier 414 goes to zero. This provides a nega-
tive t;rigger to one-shot 434, the negative voltage being
limited by the series resistor and parallel diode combination
in the input to one-shot 434. One-shot 434 then provides a
fixed voltage pulse for 1.9 milliseconds to resistor 432 at
the input of operational amplifier 414 to hold it at zero
volts (actually -0.6 volts because of the series diode). This
corresponds to a fixed relaxation period in the vocal cord
oscillation. All other times in the wave form, except for
the 0.3 millisecond delay, will shorten proportionally to
increased current as the resistance provided by pitch/inflec-
tion switch 406 decreases (i.e. switch 406 is pressed harder).
The total time of the oscillation cycle when switch 406 provides
a resistance of 10,000 ohms is 6.6 milliseconds (1.7~ 0.3~
1.7+ 1.0~ 1.9 millisecond), which represents about 150 Hertz.
When "m" switch 408 is closed, the resistance there-
from causes a different feedback path to be formed around
operational amplifier 463 of tunable formant filter 166. This
reduces the amount of signal going to operational amplifier
468 of fixed filter 202, especially at the higher fre~uencies.
When "n" switch ~10 is closed, resistor 477 and capacitor 478
have no effect, but the high frequencies going into operational
amplifier 468 are attenuated by the filtering action of resis-
tor 476 and capacitor 478~. As mentioned above, the output
of amplifier 468 provides the signal input to formant filter
168. Capacitor 484, located at their junction, attenuates
noise and other frequencies too high for filter 168.
Consonants are produced by the operation of the
selected one of keys 28 through 38. Assume that a ~oiced
fricative such as a "v" or "z`' is desired and no plosive keys
35 -
, ,i
~21~'70~L
(keys 33 through 38) are depressed; thus, the voltage on
membrane 502 is æero as a result of the output from OR gate
520 being zero. When the right side of key 32 is depressed,
a high signal voltage (i.e. +5 volts~ will be produced on
lines 554 and 556 from the output of the debounce circuits
associated with key 32 and membrane 502, respectivelyO This
causes a signal FR coming out of OR gate 508 to have a high
voltage. This signal is inverted and applied to pin 9 of sound
generator 532, thereby removing the previously applied in-
hibit signal. A high FR signal also produces a high VSTOPsignal coming out of OR gate 536.
me voiced fricative signal ~F on line 556 becomes
inverted by inverter 546 and enables modulator 540 and opens
CMOS switch 5~8. As mentioned above, this prevents the noise
signal produced by sound generator 532 from directly affecting
consonant filter 176. Instead, the noise-modulated VMODIN
waveform switched by transistor 542 is presented at the con-
sonant filter input.
With line 554 going high as a result of the right
side of switch 32 being depressed, the corresponding CMOS
switches in resistor banks 510 and 511 are closed. This causes
the resistance applied to sound generator 532 by resistor bank
510 to be the resistance of the parallel combination of resis-
tor 550 and 82 kiloohms. Closing the appropriate CMOS switch
of resistor bank 511 sets the gain of amplifier 306 in con-
sonant filter 176 by placing the 220 kiloohm resistor in
parallel with resistor 320, resulting in a high gain for a
high formant frequency.
The attack or rate of rise in the amplitude of the
30 noise output from pin 13 of sound generator 532 is determined
by the combination of a capacitor 558 at pin 8 of sound gen-
erator 532 and resistor 560 applied at pin 10 of sound generator
- 36 -
12~7~31;
532. A second resistor 562 in parallel with resistor 560 is
not applied at pin 10 because of switching tran~istor 564
being turned off as a result of a zero output ~rom OR gate 520.
~owever, when a plosive consonant switch is depressed (i.e.
one of switches 33 through 38), the output from 0~ gate 520
will be high and transistor switch 564 wi71 be turned on
placing resistor 562 in parallel wi-th resistor 560. 3ecause
resistor 562 has a much lower resistance, the effect of the
two parallel resistors will effectively be that of only the
resistance of resistor 562. This results in a very rapid rise
time for plosive consonantsO
The generation of the fricative consonant `'s" is
similar to that generated for consonant "z". Line 554 still
goes high, but now line 556 and thus VF signal is low. Line
556 being low causes MOD to be high. With two high inputs into
AND gate 538, the VOICE will be highO In addition, VSTOP
will also be high, and the net result is that the voicing
signal will be terminated as long as the left side of switch
32 is depressed. The n~ise clock frequency for sound generator
20 532 and the ~requency selected of consonant formant filter 176
will be the same as mentioned above for the application of the
consonant "z". Furthermore, the modulator 540 will be held
conducting or inactive as a result of ths constant application
of a high voltage at one of the inputs to OR gate 543. This
has the effect o~ inhibiting any signal input from sound gen-
erator 532 to the other input of OR gate 543. A high MOD
signal also closes CMOS switch 548, thereby providing the white
noise from pin 13 of sound generator 532 to consonant filter
176. This results in the `'s" sound being produced.
Those plosive consonants having similar sound are
paired by OR gates 524, 525 and 526. These pairs are "t"
and "d", "k" and "g", and llpll and "bl'~ The resulting outputs
- 37 -
~lZ~70~
from the particular OR gate switches in the corresponding
noise clock resistor o~ resistor bank 510 and sets the gain
of consonant fil-ter 176 by switching in the appropriate gain
resistors of resistor bank 511. Plosive consonants "tl` and
"d" have the highest formant frequency. Thus, the operation
of keys 33 or 36 does not switch any resistor of resistor
bank 511 into the circuit, and the gain of amplifier 306 is
determined only by resistor 320. As men-tioned above, the de-
pression of any corresponding plosive consonant key causes
membrane 502 to have a high voltage, thereby overriding any
fricative consonant.
The plosive sounds are generated following the
release o the key. During t~e key closure, an initial silence
results, the duration of which is determined by the operatorO
When the key is released, the corresponding switch signal goes
low and the trigger input to the correspondin~ one-shots 513
through 518 is energized. This results in the Q output of
that one-shot to go high for the predetermined, ~ixed time
delay. By combining the ~ outputs of one-shots 513 through 518
in OR gate 5~2, a timed signal is produced at the output of OR
gate 522 whene~er one o~ the plosive keys is operated. It is
during this time that the consonant sound is produced. The
negative transition when the particular one-shot times out
triggers one-shot 528. As mentioned above, this inserts a
short silent period following the plosive burst.
With reference now to Figure 10, a microcomputer con-
trolled speech synthesizer is depicted. The microcomputer
includes a microprocessor 602 and a ROM (read-only memory) 604.
Microprocessor 602 is preferably one that h~s-a very fast cycle
30 time, such as the 16-bit microprocessor TMS 9995 manufactured
by Texas Instrument. The clock of microprocessor 602 is de-
termined by a crystal 606 and preferably is bet~een 3.12 MHz to
- 38 -
3~2~
11 MHz. ROM 60~ is preferably an 8K by 8-bit read-only
memory -that has an access time that is compatible with the
clock of microprocessor 602.
The TMS 9995 microprocessor has the advantages of
including an integral 256 by 8 bit RAM and a 16 bit timer for
real time operations. In addition, this microprocessor has
very fast multiplication and division capabilities with digital
numbers. In addition, this microprocessor interfaces well with
a voice synthesizer integrated circuit 608 manufactured by the
same company (TMS 5220), the microprocessor needing only about
2% to 4% of its time to service voice synthesizer 608.
The main computer program stored in ROM 604 commands
microprocessor 602 to determine the resolution and pitch/
inflection force from playing board 42' (Figure 2). mis
input is represented by transducers 48, 50, 52 and 54 coupled
to amplifiers 68, 7~, 72 and 74, respectively. The outputs
from amplifier 68, 70, 72 and 74 are fed to the inputs of a
multiplexing analog-to-digital (A-D) converter 610. Such a
converter can be of the type AD 7581 manufactured by Analo~
Devices.
A-D converter 610 continuously scans the inputs at
a high speed and stores the most recent data values in its own
8 byte by 8 word RAM in synchronism with the microprocessor
clock. Thus, microprocessor 602 can access the information in
converter 610 simply by performing a memory fetch operation.
The main computer program uses the data stored in converter
610 to calculate the coordinates of the playing surface posi-
tions and then determine the appropriate formant frequencies
and band widths required for producing the desired vowel sound.
Alternatively, a look-up table can be used. Microprocessor
602 also translates the calculated or determined formant fre-
quencies and band widths into reflection coefficients for voice
- 39 -
~L2~701
synthesi~er 608. For a TMS 5220 speech synthesizer, this
means translating the formant frequencies and bandwidths into
reflection coefficients for the 10-pole Linear Predictive
Coding speech synthesis. The on-board RAM of microprocessor
602 can be used to store both the reflection coefficients
and the pitch/inflection information for appropriate transfer
to voice synthesizer 608_
Voice synthesizer 608 signals microprocessor 602
for more data over an interrupt line 609. This can occur
approximately every 40 milliseconds for a TMS 5220. The com-
puter program in ROM 604 includes a conventional interrupt
service routine for transferring this information to the speech
synthesizer. For this purpose, an ~-bit data bus 612 and a
16-bit address bus 614 interconnect microprocessor 602, ROM 604,
and converter 610. In addition, data bus 612 is connected to
voice synthesizer 608.
The consonant keys 26 through 38 of Figures 1 and 2
are schematically indicated on a keyboard 616. Consonant key-
board 616 is connected to data bus 612 through a keyboard
encoder 618. An appropriate encoder 618 is the type AY 5-2376
manufactured by General InstrumentO A "key down" output from
keyboard encoder 618 is connected to microprocessor 602 through
a second interrupt line 620. The computer program stored in
ROM 604 also has an interrupt service routine initiaked by a
signal on interrupt line 620. Preferably, this service routine
also deselects any other device which may have been connected
to data bus 612. This is accomplished through control gates
621, which provide Chip Select, Read Select, or Write Select
signals to the inputs of the other devices.
The data sent to data bus 612 by keyboard encoder
618 is used by microprocessor 602 to determine which consonant
key was depressed. Microprocessor 602 uses a look-up table in
- 40 -
~2~
ROM 604 to determine a starting memory address based on which
key was depressed. This starting address is transmitted
to speech synthesizer 608 over data bus 612. Working in
tandem with voice synthesizer 608 is a speech memory RO~ 622
such as a TMS 6100 manufactured by Texas Instruments. The
address delivered to speech synthesizer is in turn delivered
to ROM 622 over 4 address lines in a five step data transfer
se~uence. The reflection coefficients and other amplitude
parameters are then loaded into voice synthesizer 608 from
ROM 622 over bi-directional address lines Ai under the control
of signals on MoMl lines 623 and 624, respectively. When the
sounding of an allophone corresponding to the depressed con-
sonant key is completed, a stop command is provided causing
a READY output from voice synthesizer 608 to go low~ This
signal is transmitted by control gates 621 to microprocessor
602. Thereupon the microprocessor will be commanded by the
computer program to resume loading the current vowel formants
directly into voice synthesizer 608. Alternatively, when there
is no pitch/inflection input, a stop command can be loaded
into speech synthesizer 608 to cause it to wait in silence for
the next input. Voice synthesizer 608 directly generates
appropriate speech wave forms and provides them to its output,
to which is connected an audio amplifier 626 and a speaker 628.
In an alternative embodiment, keyboard encoder 618
can be eliminated by dividing the consonant ]ceys into four
groups of four to five keys in each group and to assign a
different voltage to each key within a group~ Signal wires
from each group can then be connected to an analog-to-digital
converter of the type used for converter 610. As micropro-
cessor 602 detects a non-zero input on one of these channels,
it reacts as if an interrupt had been received. m e identi-
fication of the key that was pushed is made by inspecting the
, - 41 -
~2~
magnitude of the voltage bits stored by the converter.
Other variations are possible in a digital speech
synthesizer. For example, other voltage inputs can be supplied
to the multiplexing analog-to-digital converter inputs. These
could include the coordinate and pitch/inflection voltages
discussed above with respect to Figure 3, or the coordinate
signals of a keyboard input, discussed below with respect to
Figure 11. The pitch/i~flection voltages could be set by a
voltage such as VVN (Figure 8). By utilizing multiplying
digital-to-analog converters and successive approximation
registers in the circuit depicted in Figure 3 to replace a
pair of analog multiplier/dividers, the coordinate positions
may be directly obtained in a digitized form. Obviously,
other microprocessors and other speech synthesizers can be
used with appropriate changes in the circuit.
With reference now to Figure 11, a multi-layer device
702 capable of indicating the coordinates of the loca~ion being
depressed is depicted. Device 702 is comprised of a substrate
704 on which a resistance layer 706 has been deposited. Sub-
20 strate 704 provides the physical support for device 702. The
combined resistances of substrate 704 and resistance layer 706
is preferably in the range of 100 ohms per square centimeter
to 50,000 ohms per square centimeter, and preferably is in the
center of that range~ Mounted along the edges of the two ends
of resistance layer 706 are a first conductive strip 708 and a
second conductive strip 710. Strips 708 and 710 permit a sub~
stantially horizontal electric field to be generated when
voltages are applied thereto.
A flexible conducting layer 712 is mounted above
resistance layer 706 and spaced therefrom by a plurality of
insulator beads 714. Insulator beads 714 permit contact
between conductive layer 712 and resistance layer 706
- 42 -
o~L
whenever localized pressure is applied on device 702. Insula-
tor beads 714 can be in the form of glass or plastic spheres,
or may be paint or varnish droplets applied, for example, by
silk-screening or by being sprayed. Conductive layer 712 can
be comprised of a sheet 716 preferably of an insulating plastic
film of polystyrene, polyethylene terephthalate (known by the
trademark "MYIAR'`). The underside of sheet 716 has a coating
718 of a conductive material. Sheet 716 must be thin enough
so that it can be deflected downwardly when pressure is applied
thereon, but be thick enough to resist stretching or any
lateral movement. Coating 718 preferably has a resistance
that is less than 100 ohms per square centimeter. ~he topside
of sheet 716 has a second coating 720 having approximately
the same resistance parameters as resistance layer 706. Mount-
ed along the two transverse edges and extending longitudinally
are a third conductive strip 722 and a fourth conductive strip
(not shown). A terminal 724 is connected to conductive coat-
ing 718.
A top cover sheet 726 is mounted on top of sheet 716
and spaced therefrom by a plurality of beads 728, similar to
beads 7140 Cover sheet 726 is also preferably of a plastic
film such as polyethylene terephthalate ("MYLAR"). A conduc-
tive coating 730 is located on the under surface of cover sheet
726. Conductive coating 730 preferably has a low resistance
that is less than 100 ohms per square centimeterO A terminal
732 is connected in electrical contact with coating 730. The
upper surface or top surface of cover sheet 726 forms playing
surface similar to playing surface ~2 of Figures 1 and 2. The
IPA symbols for the vowel sounds can be embossed or marked
thereon. Preferably, however, to prevent the symbols from
being removed through use, cover sheet 726 should be trans-
~arent and the symbols should be printed on the underside of
cover sheet 726 above conductive coating 730.
- 43 -
~Z~9~
Moun-ted on first conductive strip 708 is a terminal
734 for the application of a suitable positive voltage (e.g.
+S volts or ~15 volts). A ground terminal 736 is located on
the opposite conductive strip 710 for the connection of a
ground potential. Similarly, a positive voltage terminal 738
is located on the bottom or third conductive strip 722 and a
corresponding ground terminal (not shown) is connected on the
top conducting strip (also not shown). Thus, it sho~lld be
apparent that when suitable power connections are made to
10 terminals 734, 736, 738 and the fourth, ground terminal, and
when pressure is exerted on top of device 702~compressing the
various layers, an output voltage will appear on VH terminal
724 andVv terminal 732. The output voltages will be propor-
tional to the distance from positive voltage terminals 734 and
738. rrhusl the output signal VH goes from the applied positive
voltagP to zero volts when pressure is moved from the right to
the left as depicted in Figure 12, and similarly, output signal
VV goes from the applied positive voltage to zero volts when
the pressure is moved from the bottom to the top of device 702
20 as depicted in Figure 12. When device 702 is used in a
synthesizer circuit according to the present invention, it
will be the position resolution circuit 160 as depicted in
Figures 5 and 6 and signals VH and Vv will be provided at
outputs 162 and 164. The lower these voltages will be, the
higher the formant frequencies provided by the corresponding
formant filter 166 or 168, respectively.
~eferring now to Figure 13, a second embodiment of
a specific input board or device 802 is depicted. Device 802
is comprised of a substrate 804 and a cover sheet 80~, shown
separated from substrate 804. Located on top of substrate
804 is a resistive coating 808. Preferably, the total resis-
tance of both resistive coating 808 and substrate 804 is about
r ~.
'~ ' 44 ~
1000 ohms per s~uare centimeter, but a higher or lower order
of magnitude of resistance would be acceptable. Deposited
on the bottom or underside of cover sheet 806 is a conductive
layer 810 preferably having a resistance less than a hundred
ohms per square centimeter. A terminal 812 is in electrical
contact with conductive layer 810. Cover sheet 806 can be
similar to cover sheet 726 and made of a transparent, "MYLAR`'
(polyethylene terephthalate) on which is printed the IPA
phonetic symbols. An annular piece of insulating sheet mater-
ial 814 is adhered to the underside of cover sheet 806. A
pluralit~ of insulating beads (not shown), but similar to beads
714 and 728 in Figures 11 and 12, are adhered to the surface of
resistive coating 808. In an assembled embodiment of device
802, cover sheet 806 is adhesively mounted or otherwise secured
on top of substrate 804 and resistive coating 808, separated
from the latter by the insulating beads.
Mounted around the edge of substrate 804 in contactwith resistive coatin~ 808 are two power terminal contacts, a
ground terminal contact 816 and a positive voltage terminal
contact 818. In addition, a large number of signal terminal
conkacts 820 are located around the periphery of substrate
804 in electrical contact with resistive coating 808. Con-
tacts 816, 818 an~ 820 can be accurately located and applied
onto resistive coating 808 by a number of methods including
silk-screening, printing, spraying or painting. Suggestive
materials for these contacts are conducting epoxies or a
conducting silver paint. The ratio of the widkh of contacts
816,-818 and 820 to the space ~etween the contacts should be
within the range of 1:1 and 1:3. By making the area occupied
by contacts 816, 818 and 820 to no more than 25% to 50% of
khe annular strip in which the contacts are located, minimum
distortion of the voltage field will occur at the edges due
- ~5 -
7~
to the short-circuiting effect of the conductive contacts
on resistive coating 808.
Four banks o~ switching transistors 822, 823, 824
and 825 are electrically connected to the left hand side, the
top, the right hand side, and the bottom signal terminal
contacts 820, respectively. The transistors in transistor
bank 822 and 825 are connected as a comrnon collector trans-
istor array and the transistors of transistor banks 823 and
824 are connected together as a common emitter transistor
array. Exemplary transistors of transistor banks 823 and
824 are CA 3081 transistors manu~actured by RCA and e~emplary
transistors for transistor banks 822 and 825 are CA 3082
transistors manufactured by RCA. The collectors of transistor
banks 822 and 825 are connected to a positive voltage connec-
tion. The emitters of transistor banXs 823 and 824 are con-
nected to ground. A diode 828 is connected between the
positive voltage and contact 818 so as to provide about the
same voltage drop as the transistors in transistor banks 822
and 825. As thus arranged, transistor ~anks 822 and 824 pro-
vide a switchable horizontal (as depicted in Figure 13) elec-
tric field and transistor banks 823 and 825 provide a switch-
able vertical electric ~ield.
The output from device 802 is taken from terminal
812 by an output line 830. Output line 830 ! in turn, is
connected through two CMOS switches, a vertical ~MOS switch
832 and a horizontal CMOS switch 834, to a vertical ~ignal
storage capacitor 836 and a horizontal signal storage capaci-
tor 838, respectively. The electrical output from device 802
is provided by two operational ampli~iers, a vertical signal
operational amplifier 840 and a horizontal signal operational
ampli~ier 842, each connected as a high input impedance follow-
er. The outputs from operational amplifiers 840 and 842 follow
46 ~
~2~
the voltage on capacitors 835 and 838, respectively, without
drawing much current ~rom them.
The gates of the transistors in transistor banks 823
and 825 and the gate of CMOS switch 832 are all connected
together to a common line 844, and the gates of the transistors
of transistor banks 822 and 824 and the gate of CMOS switch
834 are all connected together to a common line 846. A low
frequency oscillator 848 is directly connected to and pro-
vides a scanning waveform to line 844, and is connected to
line 846 through an inverter 850, thereby providing a phase
shifted scanning waveform to line 846. Oscillator 848 can
simply be comprised of two CMOS invertersl two resistors and
one capacitor (not shown), Preferably, the scanning waveform
is a square wave having a fre~uency in the range of 100 Hz
to 100 kHz frequency. A current-limiting base resistor 852
is connected to the base of each of the -transistors in trans-
istor banks 823 and 824. ~esistors 852 can have an exemplary
resistance of 10,000 ohms.
In operation, capacitors 836 and 838 are alternately
connected to output line 830 through switches 832 and 83~,
respectively, operated in sequence by the scanning waveform
and the phase shifted scanning waveform applied to lines 844
and 846, respectively. Thus, capacitors 836 ~nd 838 are
alternately connected to any voltage applied to conductive
layer 810 of device 802. When the individual signal in the
phase shifted waveform applied line 846 is high, the transis-
tors of transistor banks 822 and 824 are turned on, causing a
horizontal voltage gradient across resistive coating 808.
Downward pressure on cover sheet 806 connects output line 830
to a small zone of the resistance coating 808 directly under
the point of pressure. The voltage at the point of pressure
is delivered to output line 830. Since CMOS switch 834 is
- 47 -
turned on at the same time that the transistors of transis-
tor banks 822 and 824 are turned on, voltage under the point
of pressure also appears across capacitor 838 after a rela-
tively small time delay. Consequently, this voltage also
appears at the output of operational amplifier 842.
When the horizontal vol~age gradient is turned off,
a vertical voltage gradient is applied to resistive coating
808 as a result of the operation of the transistors in trans-
- istor banks and ~323 and 825. The amount of voltage at the
point of pressure will appear across capacitor 836 in a
fashion similar to the charging of capacitor 838. Capacitors
836 and 838 hold the voltage during the time that their res-
pective CMOS switch is open. In this manner, an analog voltage
signal representative of the horizontal location of the pres-
sure point and representative of the vertical lo~ation of the
pressure point will respectively appear as output signals VH
and V~ at the outputs of operational amplifiers ~42 and 840.
Device 802 provides an input terminal having good
linearity up to the edges of the inner playing space defined
by signal contacts 820. It also provides mechanical simplic-
ity and a one contact point between a resistive coating and a
conductive film instead of the two contact points of device
702 in Figures 11 and 12. Conse~uently, device 802 of Figure
13 has a relatively low manufacturing cost and a high degree
of reliability.
Thus, there is disclosed herein a speech synthesizer
that can be "playedl' live and will form natural sounding words
according to the motions of the hands of the operator. Such
a device can be used as a prosthesis for those persons who have
lost their voices or who have a speaking im~airment. In one
embodiment, the speech synthesizer is "played" on a two-dimen-
sional surface over which the fingers of the operator range to
- ~8 _
, .
~Z~}~7~
sound any of the vowels, dipthongs, or semi-vowels together
with a selection area where fricativ~ or plosive consonants
can be individually selected. A further feature operable
separately or derived from the total pressure applied to the
playing surface adds a control of the pitch and/or inflection
of the voicing source~ The formation of the sounds can be
done using either an analog synthesizer or a digital syn-
thesizer.
m e present invention can also be used for applica-
tions other than as a prosthesis. For example, it can be usedto teach the principles of formation of human speech~ The
present synthesizer never runs out of breath and can sustain
a tone continuously. The exciting waveform can be listened to
and displayed on an oscilloscope and observed as various vowels
are sounded~ A second synthesiser can be connected to a fre-
quency spectrum analyzer to show what is happening to the
amplitude response versus frequency as various vowel sounds
are produce~ on the first.
Another educational and research application of the
present invention is in the field o~ linguistics to match the
vowel and dipthong sounds of regional speech. For example,
the present invention can say "you all" with a Southern drawl
that is quite convincing. Once determined, the various sounds
can be cataloged by reference to the horizontal and vertical
coordinates~
A digital embodiment of the present invention can be
used to produce a stream of diyital bits to some form of
digital memory. In this manner, the speakiny vocabulary for
a digital synthesizer càn be expanded to create words not
only in the English lanyuage but in any language. This would
be a very economical way of producing custom encoding of words.
The baud rate of the present invention is relatively
- 49 _
o~
low, on the order of six hundred bits per second. In the
analog embodiment of the present inve~tion there are three
signal par~meters which change only slowly with time. These
signals may be multiplexed and transmitted using conventional
techniques over limited bandwidth facilities, or they may be
digitized with an analog-to-digital converter. If saved in a
digital form, a smaller amount of memory space is needed
compared to the space required ~or Linear Predictive Coding.
The touch-sensitive tablet of the present invention
can also be used as a control for video games or as a tracing
tablet for providing graphs, maps and handwriting information
to a computerO
While the present invention has been described with
respect to specific embodiments thereof having specifically
enumerated advantages.and objectives, it should be obvious
to those skilled in the art that alternative embodiments and
alternative objectives are possible using the teachings
disclosed hereinabove.
,; - 50 -
9L2~0~
T~3LE 1
Resistors (ohms) Capacitors (microfarad)
R302 - lOOk (potentiometer) Cl - .001
R310 - 22k C2 - .66
R312 - 2.7k C3 - .33
R314 - 22k C416 - Ç.8
R316 - lOOk C420 - .039
R320 - 47k C440 - .0047
,R322 - 1.8k C465 -O047
R324 - lOOk C473 ~ .01
R326 -lOk C474 -.01
R326t-22k C478~-.047
R358 -lOk C478 -.047
R360 -lk C481 -.047
R378 -lOk C484 -.001
R380 -20k C492 -.001
R402 - lOOk (potentiometer)C558 - .33
R404 - lOOk (potentiometer)C836 - .1
R418 - 120k C838 -.1
R423 - 15k C495 - .0047
R424 - lOOk
R426 - lOOk
R428 - 18k
R430 - 5.6k
R432 - 22k
R450 - 516k
R454 - 33k
R456 - lOk
R458 - 75k
R459 - 22k
- 51 -
~2C~9~0~
TAB_E_l - Cont.inued
R460 - lOOk
R461lk
R466 -22k
R470 -68k
R472 -27k
R475 -22k
R476 -22k
R477 -18k
R479 -47k
R480 -47k
R482 -330k
R483 - lOOk
R486 - 8.2k
R487 - 33k
R488 - 330k
R489 - 82k
R491 - lOk
R550 -330k
R560 -330k
R562 -22k
R320'-470k
R436 -15k
R437 -39k
R442 - lOOk
R852 - lOk
- 52 _
70:1:
- TABLE 2
I C. Number
4528 - One shots 434, 438
741 - Operational ~npli:fiers 412, 414,
448, 462, 463, 464, 458, 490
4066 - CMOS gates 485, 548
~: - 53 -
