Note: Descriptions are shown in the official language in which they were submitted.
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7154 8--9D
This application is a division of my Canadian patent
application Serial No. 44Q,085 filed October 31, 1983.
~ his invention relates to electronic, stringed
musical instruments and more specifically, it relates to the
use of resistance wires as strings which control the Erequency
of electronically generated sounds in such instruments~
It has been known to vary the resistance in a
Wienbridge oscillator in an electrical circuit associated with
a musical instrument. See United States Patent No. 3,624,584.
United States Patent No. 3,626,350 discloses a means to produce
a portamento chord by utilizing this principle.
United States Patent No. 3,948,137 discloses prior
art which allows the player of an instrument utilizing a
voltage controlled oscillator to control sound effects by
providing wave form, filter and gain controls.
United States Patent No. 4,235,141 discloses an
instrument wherein an apertured insulating strip is inserted
between an electrically conaucting strip and a resistive strip
to only allow contact points at predetermined locations, there-
~0 by producing a tone at discrete selected values of frequency.
Electrically synthesized music is an increasinglypopular art form in which substantial technological advances
have been made. In the past, however, most of these advances
could only be utilized in a keyboard type instrument excluding
musicians skilled primarily in the playing of stringed instru-
ments.
A known attempt to provide a voltage controlled
electronic stringed instrument is United States Patent
No. 4,038,897.
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In this patent, a guitar or other fretted instrument is used to
produce input signals for a voltage-controlled tone generator
or the guitar can be used in the coventional fashion by
operating a switch. Each string-fret pair has an assigned
musical tone. Voltages analogous to said tones are applied to
the instruments frets so as to apply such voltage to the
strings when the strings contact the frets.
Such systems have several major limitations.
Firstly, the invention is limited to fretted stringed
instruments. Additionally, complicated wiring of resistors to
each fret is required in order to provide each with the proper
voltage value. Finally, providing the voltage to electrically
conducting frets appears to foreclose the possibility of
playing chords without fret segmentation.
There remains, therefore, a need for a stringed
electronic instrument which provides effective frequency
control in either fretted or unfretted string instruments
employing the strings as resistance and a means for playing
chords whether or not frets are desired.
SUMMARY OF THE INVENTION
The present invention has produced a solution to the
above need by providing an instrument which uses electrical
resistance wires as strings to control the frequency of
electrically generated sounds. The frequencies are produced by
voltage to frequency converters or other suitable circuits.
More specifically, the variable voltage output that controls
frequency is obtained by shorting at various points along its
length a constant electrical current supplied to a string.
This shorting operation can be employed in two distinct classes
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of stringed instruments. In a guitar or other fretted instru-
ments the resistance strings can be shorted at any single fret
providing a means to incrementally control the voltage output
of the instrument~ In a violin or other non-fretted instru-
ments the surface of the fingerboard facing the strings can be
made of an electrical conducting material so the resistance
strings can be shorted at any point providing a means to
variably control voltage output.
Each string is provided with a separate current
source but all strings are referenced to the same grounding
point. The frets or the entire conducting surface of the neck
in the case of a violin type instrument are also grounded. The
non-grounded end of each string is connected to a current
source. The voltage drop is detected so that the strings do
not interfere with each other at the frets and consequently,
chords can be played.
In the past, most voltage controlled electronic
instruments employed Wien-bridge oscillators or similar
circuits which required relatively high resistance values for
the control element. The present invention, however, utilizes
a voltage to frequency converter circuit which can be control-
led by relatively low resistance values as the voltage can be
amplified before conversion, making possible the use of low
resistance wires as the control elements. Furthermore, the
high stability of the resistance, the constant current sources,
and the precision of commercial voltage to frequency converters
will make this type of instrument of professional quality.
The embodiments of the present invention provide a
means for controlling the intensity and harmonic content of the
signals produced. More specifically, suitable attenuators and
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filters are controlled by ~ne of the player'~ han~s while the
other presses the strings to produce the desired frequency.
Wound resistance wire strings may be provided for low notes as
well as a method for producing the same.
In one embodiment of the present invention an
internal power supply and speakér are provided to make the
instrument readily portable.
In another embodiment of the present invention a
frequency co~nter is integrated into the instrument's
electrical circuit to facilitate tuning.
It is further contemplated that combining the
electrical and mechanical strin~ produced sounds may have
potential for expanding the instruments artistic possibilities.
It is an object of the present invention to provide a
voltage controlled stringed musical instrument which utilizes
resistance wires as strings.
It is yet another object to employ resistance wire
strings in both fretted and non-fretted instruments.
It is a further object of the present invention to
utilize a constant current generator in embodiments in which a
linear relationship between the length of the string and the
frequency is desired.
It is yet another object of this invention to provide
a means to produce suitable strings for the instrument.
It is yet another object of this invention to provide
a means for controlling the intensity and harmonic content of
the sounds produced,
It is yet another object of this invention to provide
a self-contained package including a speaker and internal power
source so as to make said instrument readily portable.
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In accordance with a broad aspect of the
invention of this divisional application there is provided
a method for producing a wound string for a voltage controlled
stringed instrument which utilizes resistance wires as strings
to control the frequency of electronically generated sounds
comprising the steps of: tightly winding well insula-ted resis-
tance wire about a core, dipping said wound string into a
suitable resin, and removing said insulation and resin from
the outer surface of said wound string.
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These and other objects of the invention will be
fully understood from the following description of the
invention on reference to the illustrations appended hereto.
BRIEF DESCRIPTION OF ri~E DRAWINGS
Figure 1 is a schematic view of one form of the
invention showing an electrically insulating fingerboard and
conducting frets.
Figure ~ is a cross-sectional view of the fingerboard
shown in Figure 1 taken through 2-2 of Figure 1.
Figure 3 is a schematic circuit diagram of a circuit
to provide a suitable constant current source for the instru-
ment.
Figure 4 is a cross-sectional view of a wound
resistance wire string.
Figure 5 is a block diagram of the various steps
involved in converting changes in the string resistance into
frequency signals of desired quality characteristics.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As used herein, in the absence of a clear, express
indication to the contrary at a specific location, the tèrms
"string" and "strings" refer to either straight or wound
electrically conductive resistance wires~
As used herein, in the absence of a clear, express
indication to the contrary at a particular location the terms
"conducting" and "insulating" refer respectively to a materials
capacity to conduct or to resist the conduction of an electri-
cal current.
The present invention provides a musical instrument
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which varies the input voltage in an electr;cal circuit and
converts the voltage to a frequency to produce a responsive
musical tone. The voltage (V) in the circuit is dependant upon
two variables, current (I) and resistance (R) according to
V=IR. It is preferred, but not required, to provide the
instrument with a constant current source of power which
results in a linear relationship between the voltage and
resistance. The instrument's strings provide the resistance
element in the circuit. By urging a string against a con-
ducting surface at differenct points along the string's lengththe circuit's resistance and the resulting voltage drop can be
effectively controlled and varied.
Referring more specifically to Figures 1 and 2
(wherein for clarity of illustration the strings have not been
shown), one embodiment of the present invention, a guitar type
fretted instrument is shownO The instrument 3 has a body 6
having any convenient shape and preferably is made of a rigid
electrically insulating material. One end of neck 9 is secured
to the body as by conventional means. The neck 9 is also
preferably an insulator but both the neck and body may be
conductors if desired. A rigid insulating fingerboard 12 is
attached to neck 9u A hardwood or rigid plastic would be a
suitable material to construct the fingerboard 12. An
insulating bridge 15 is also secured to the body 6, so as to
provide a means to elevate the strings a slight distance above
the fingerboard 12.
A plurality of conducting frets 16 are embedded
across the fingerboard 12 at desired points along its length.
The fret spacing may remain essentially the same as in regular
guitars, and the current can be adjusted to correspond to the
same notes. The frets 16 are preferably made from a hard
conducting metal such as stainless steel. Embedded at the end
of the fingerboard 12 farthest away from the body 6 is a rigid
conducting shorting bar 18 to support the strings (not shown) a
slight distance above the uppermost fret 16.
Each of the frets 16 are electrically connected
together in series and connected to the electrically grounded
shorting bar 18 by a conductive connecting wire 30, as shown in
Figures 1 and 2. The frets 16 may be connected together and to
the shorting bar by any other suitable means such as a
conducting strip mounted under the insulating fingerboard 12
which contacts each of said frets 16.
The strings (not shown) are attached to the
instrument by conventional means and, as mentioned, are
supported above the frets on one end by the insulating bridge
15 and at the other end by the shorting bar 18. The strings
are tuned mechanically by adjusting their tension by turning
tuning keys 26 in the usual fashion. Electronic tuning of each
string is accomplished by turning a potentiometer knob 27
suitably wired into the circuit by means well known in the
art. A frequency counter 33 may also be integrated into the
circuit to facilitate tuning. A constant current power source
and amplifier circuit 28 ~see Figure 3) is connected to each
string at or near the bridge lS by any suitable means. It is
preferable to make these connections at points 29 to avoid
interference with the strings mechanical vibration. Points 29
may also serve as the input to an amplifier. It is contem-
plated that an internal power supply 42 and speaker 45 could
also be provided to make the instrument more portable. It is
preferable to keep the resistance values of the strings below
r~ s ~ s J~ ~
,~ 1000 ohms so that the changes in finger contact }~i~ta~ do
not play a perceptive role, unless such an effect were
desired. Contacting a string to a chosen fret will complete an
electrical circuit and create a desired voltage output which is
then converted into a frequency signal by means well known in
the art. Such voltage to frequency converters are now avail-
able as commercial intergrated circuits.
It will be appreciated by those skilled the art that
by eliminating the frets and replacing or covering the insul-
ating fingerboard with a sheetlike conducting fingerboard, aviolin type non-fretted instrument will function essentially as
described above. With this embodiment continuous variability
of pitch can be achieved.
The present invention also provides a means for
controlling the harmonic content and intensity of the signals
produced. First, the pitch or fundamental frequency is select-
ed by means of a particular string. Harmonic frequencies are
then selected by color control registers 39.
It is contemplated that the loudness can be effec-
tively controlled in one of two ways. In one embodiment,thestrings would be plucked or ban9ed as in conventional instru-
ments Below each string would be placed an electromagnetic
pickup 31 as is done in conventional electric guitars. The
output of this pickup would then be amplified and rectified to
derive the intensity envelope of the vibration, which is
proportional to loudness. This loudness envelope voltage would
then be used to control the loudness of the electronic sound by
means of voltage controlled amplifiers.
In another embodiment of the present invention, it is
contemplated that suitable pressure transducers 32, which can
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respond properly and rapidly to ~inger pressure, could be
manipulated by the players free hand to control loudness. The
above mentioned pressure transducers could be in the form of
buttons, perhaps one to control each string or any combination
of strings. The voltage from these transducers would be
applied through a voltage controlled amplifier to effectively
control loudness. The separate control of the duration and
loudness of each note in a chord is made possible by the use of
this method, thereby, allowing for greater flexbility and
creative potential.
Figure 3 shows a schematic circuit diagram of a
typical circuit to provide a sui~able constant current source
for this instrument and the first stage of amplification. The
constant reference voltage -Vz is obtained by means of the
Zener diode 80 and the resistor 81. The resistor network R3,
R2 and RT apply a fraction of this voltage to the non-inverting
input of the operational amplifier 82. The inverting input is
connected to the resistor Rl in which the voltage drop is
proportional to the current IS which flows through the control-
ling field-effect transistor 83 and the string 84 with the
effective resistance Rs. The voltage drop over RS is ISRs.
This is fed to the amplifier 85 with the provision to adjust
the gain by means of the control 86. The value of the constant
current IS can be adjusted by means of the tuning control 87
through the relationship IS = V~R3/Rl (R2+R3+RT).
Figure 4 represents a cross-sectional view of a
string wound with resistance wires for low notes. A steel wire
75 of suitable diameter is used for the core. A well insulated
resistance wire 77 is then tightly wound onto wire 75. The
whole string 79 might then be dipped into a suitable resin
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(such as epoxy) to tightly fixate the insulation 78 in order to
prevent electrical contact towards the core and between the
turns on account of abrasion due to internal flexing. The
insulation 78 would then be removed as by sanding only on the
string's outer surface so that the string can make contact with
the frets.
Figure 5 is a block diagram of one embodiment of the
present invention showing the various steps in converting
voltage signals into frequency signals of desired wave char-
acteristics. As string 39 is pressed to contact fret 40 an
electrical circuit is completed. The resistance of the portion
of the string now included in the circuit will alter the
voltage in the circuit according to V=IR. By pressing the
string to contact other frets (not shown) different voltage
ouputs can be obtained. The voltage signal is then amplified
by the operational amplifier curcuit ~5 as shown. As indicated
in block 50 of Figure 5, the amplified voltage signal obtained
by the above described method is then converted into a frequency
signal. Depending on the type of voltage to frequency converter
employed the output frequency signal may be a sine wave or some
other wave form. This output frequency signal may then by
inputted into a wave shape former shown in block 55. After a
desired wave form is obtained, the basic frequency signal may
then be filtered to remove undesired "harmonics~ in the circuit
as is indicated by block 60. Block 65 shows a selectable mixer
which can be used to combine the frequency signals to produce
various coloration of the sound. The output of the mixer is
thèn attenuated as desired by a suitable circuit to control
loudness r as shown by block 70.
While I have shown and described certain present
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preferred embodiments of the invention and have illustrated a
present preferred method of practicing the same it is to be
distinctly understood that the invention is not limited thereto
but may be otherwise variously embodied with the scope of the
following claims.
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