Note: Descriptions are shown in the official language in which they were submitted.
SPECIFICATION
TITLE OF THE INVENTION
Audio Signal Reproducing Apparatus
FIELD OF THE INVENTION
The present invention relates to an audio signal binaural
reproducing apparatus for reproducing audio signals by means of
headphones.
BACKGROUND OF THE INVENTION
A binaural reproducing method has heretofore been known as
an approach for providing better direction sensation of sound
image or outside head localization sensation when audio signals
are reproduced by headphones fitted to the head of a listener so
that a pai r of headphones are 1 ocated i n the vi ci ni ty of both
ears.
An audio reproducing system adopting this binaural system
preliminarily applies a given signal processing to the audio
signals reproduced by headphones as is described in, for example,
specification of Japanese Patent Publication Sho 53-283.
The direction sensation of sound image and outside head
localization sensation and the like depend upon the differences
in volumes, times and phases of sounds listened by left and right
ears.
'fhe signal processing aims at causing in an audio output
1
~s~~s~s
reproduced by the headphones, audio effects equivalent to those
caused by the difference in distances between sound sources, that
is, speaker systems and right and left ears of a listener and
reflections and diffractions in the vicinity of the head of the
listener when audio reproducing is performed, for example, by
speaker systems remote from the listener. Such a signal
processing is performed by convolution-integrating left and right
ear audio signals with impulse responses corresponding to the
above-mentioned audio effects.
Since the absolute position of the sound image is not
changed even if the listener moves or turns his or her head when
audio reproducing is performed by speaker systems remote from the
listener, the relative direction and position of the sound image
that the listener senses are changed. In contrast to this, since
the headphones is turned together with the listeners head if the
listener turns his or her head when audio reproducing is
performed by a binaural method using headphones, the relative
direction and position of the sound image which the listener
senses are not changed.
If binaural reproducing is performed by using headphones in
such a manner, a sound image is created in the head of a listener
due to differences in displacement of the sound image relative
to a change in direction of the listener's head. Therefore, it
is difficult to locate the sound image in front of the listener.
Furthermore, the front.sound image has a tendency to lift up.
2 ~.
~~4~~~~
Accordingly, an audio signal reproducing system which
detects a change in the direction of the listener's head and
changes the modes of the signal processing based upon a result
of the detection for providing a good -Front localization
sensation in headphones has heretofore been proposed as is
disclosed in Japanese Unexamined Patent Publication No. Sho 42-
227 and Japanese Examined Patent Publication No. 54-19242- rn
such an audio signal reproducing system, a direction detecting
device such as gyrocompass and magnetic needle is provided on the
head of the listener. A level adjusting circuit and a delay
circu it and the like for processing the audio signals are
controlled based upon a result of detection from the direction
detecting device so that a sound image sensation which is similar
to that of the audio reproducing using speaker systems remote
from the listener is obtained.
In the prior art binaural reproducing system in which
headphones are provided with a direction detecting device
comprising a gyrocompass, an excellent sound image can be
obtained by controlling the content of the signal processing
which is applied to the audio signals depending upon changes in
direction of the listener's head.
Tn order to control the content of the signal processing
applied to the audio signals depending upon a change in direction
of the listener's head, it is necessary to preliminarily measure
the impulse responses, that is, transfer characteristics
3
~~~~6~s
corresponding to audio effects given to audio signals of left and
right ears for each predetermined rotational angle and to store
a great amount of information on the transfer characteristics.
The i nformati on i s read f rom the sto ri ng means dependi ng upon the
change in direction of the head. The audio signal will be
subjected to a necessary convolution-integration processing in
real-time.
The present invention was made under such circumstances.
It is an object of the present invention to provide an audio
signal reproducing apparatus having a simple structure using
storing means having a low storing capacity which is capable of
performing a binaural reproduction for providing a very natural
localization of a sound image in which the positions of virtual
sound sources are not changed by headphones even if a listener
moves by reducing the amount of information on transfer
characteristics from virtual sound sources necessary for binaural
reproduction of audio signals with the headphones to both ears
of the listener.
DISCLOSURE OF THE INVENTION
An audio signal reproducing apparatus of the present
invention comprises means for detecting the rotational angular
position of the head of a listener corresponding to the movement
of the head of the listener relative to virtual sound sources;
means for storing transfer characteristics information
4
2m~~6~s
representative of transfer characteristics of direct sounds from
virtual sound sources to both ears of the listener for each
predetermined rotational angular position in at least the first
quadrant; and audio signal processing means which based upon the
transfer characteristics information of at least one quadrant
stored in said storing means, forms the transfer characteristic
information in the rotational angular position of the head
represented by an detection output of said detecting means for
processing left and right channel audio signals, whereby the left
and right channel audio signals which have been processed by said
audio signal processing means are reproduced as sounds by
headphone means.
An audio signal reproducing apparatus of the present
invention comprises means for storing transfer characteristics
information representative of the transfer characteristics from
virtual sound sources to both ears of a listener for each
predetermined rotational angle corresponding to the movement of
a head of the listener; means for detecting the rotational
angular position corresponding to the movement of the head of the
listener; interpolation operation means which reads from said
storing means information on at least two transfer characteristic
in the vicinity of the rotational angular position of the head
represented by an detection output of said, detecting means for
interpolation-processing the read transfer characteristics
information in the rotational angular position of the head
represented by the detection output of said detecting means; and
audio signal processing means for processing left and right
channel audio signals with the transfer characteristics
information determined by said interpolation operation means,
whereby the audio signals which have been processed by said audio
signal processing means are reproduced as sounds by a headphone
set.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram schematically showing the
structure of an audio signal reproducing apparatus of the present
invention;
Fig. 2 is a time chart schematically showing signals
supplied to a operation unit of the audio signal reproducing
apparatus;
Fig. 3 is a schematic diagram illustrating the distance and
the angle calculated by the operation unit of the audio signal
reproducing apparatus;
Fig. 4 is a view for explaining the information on the
transfer characteristics stored in a storing circuit of the
operation unit in the audio signal reproducing apparatus;
Fig. 5 is a plan view showing the relative positional
relation between virtual sound sources and a listener for
explaining the operation of binaural reproducing performed by the
audio signal reproducing apparatus; and
6
2~~~6~~i
Fig. 6 is a block diagram schematically showing the other
structure of the audio signal reproducing apparatus of the
present invention.
BEST MODE FOR EMBODYING THE INVENTION
The audio signal reproducing apparatus of the present
invention comprises a headphone set 10 which is fitted over the
head M of a listener P and a pair of headphones 2L and 2R are
supported by a head band 1 so that they are located in the
vicinity of left and right ears of the listener P, respectively
as shown in Fig. 1.
Two sliders 4L and 4R from which support arms 3L and 3R,
respectively project are slidably mounted on the head band 1 of
the headphone set 10. A pair of signal detectors 5L and 5R which
detect a position detection reference signal emitted from a
reference signal source 11 are provided at the tip ends of the
support arms 3L and 3R, respectively. That is, the pair of
signal detectors 5L and 5R are provided on the tip ends of the
support arms 3L and 3R projectedly formed on the sliders 4L and
4R which are siidably mounted on the head band 1 so that they are
supported in positions remote from the head band 1 and the pair
of headphones 2L and 2R, that is the main body of the headphone
set.
In the present embodiment, the reference signal source 11
comprises an ultrasonic signal source 12 and an ultrasonic
~~4~6~~;
speaker 13 for generating an ultrasonic signal from the
ultrasonic signal source 12 as a reference signal. Each of the
pair of signal detectors 5L and 5R which receive the reference
signal comprises an ultrasonic microphone.
An ultrasonic wave generated from the ultrasonic speaker 13,
that is, the position detection reference signal is a burst wave
in which an ultrasonic wave having a given level is
intermittently generated for a given period of time as shown at
A in Fig. 2, or an ultrasonic wave, the phase of which may be
detected like a so-called level modulated wave, the level of
which changes in a given circle.
The pair of signal detectors 5L and 5R provided on the
headphone set 10 detects the ultrasonic position detection
reference signal generated from the ultrasonic speaker 13 and
generate respective detection signals shown at B and C in Fig.
2, each having a time lag depending upon the relative positional
relation between the listener P and the ultrasonic speaker 13.
Since the pair of signal detectors 5L and 5R are supported
by the support arm 3L and 3R in positions remote from the main
body of the headphone set 10 while they are mounted on the tip
ends of the support arms 3L and 3R in positions remote from the
main body of the headphone set 10 while they are mounted on the
tip ends of the support arms 3L and 3R which project from the
sliders 4L and 4R, respectively slidably mounted on the head band
1 and, the head band 1 and the pair of headphone 2L and 2R, that
8
is, the main body of the headphone set is fitted on the head M
of the listener P, they can detect the ultrasonic wave generated
from the ultrasonic speaker 13, that is, the position detection
reference signal stably and accurately without being located
behind the head P of the listener P even if the listener P moves
or rotates his head P. The pair of the signal detectors 5L and
5R can be adjusted to a position optical for detecting the
detection reference signal by sliding the sliders 4L and 4R along
the head band 1. For example, the optimal positions of the
headphones 2L and 2R which are fitted on the head M of the
listener P by the head band 1 so that they correspond to the
vicinity of the left and right ears depend on the shape and size
of the had M of the 1 istener P, that is, have the differences
among individuals. Accordingly, the positions of the pair of
signal detectors 5L and 5R can be adjusted .so that they
correspond to the headphones 2L and 2R, respectively.
Each detection signal obtained by these signal detectors 5L
and 5R is applied t o an operation unit 14.
The operation unit 14 comprises first and second edge
detecting circuits 15 and 16, to which the detection signal from
the signal detectors 5L and 5R for detecting the position
detection reference signal are supplied, respectively and a third
edge detecting circuit 17 to which an ultrasonic signal from the
ultrasonic signal sources 12, that is, the position detection
reference signal is applied.
9
~~~~~~~i
The first and second edge detecting circuits 15 and 16
detect rise-up edges of the detection signals generated from the
signal detectors 5L and 5R, respectively and output pulse signals
shown at D and F of Fig. 2 corresponding to the rise-up edges
pulse signals generated by the first and second edge detecting
circuits 15 and 16 are supplied to a distance calculating circuit
18 and a ci rcuit 19 for detecting the time difference between
both ears. The third edge detecting circuit 17 detects the rise-
up edge of the ultrasonic signal from the ultrasonic signal
source 12 and outputs a pulse signal corresponding to the rise-up
edge as shown at F in Fig. 2. A pulse signal obtained by the
third edge detection circuit 17 is supplied to the distance
calculating circuit 18.
The distance calculating circuit 18 detects the time
difference t~ between pulse signals obtained by the third and
(first edge detecting circuits 17 and 15 which is represented as
AT1 in Fig. 2 and the time difference t2 between pulse signals
obtained by the third and second edge detecting circuits 17 and
16 which is represented as AT2 in Fig. 2 and then calculates the
distance Q~ between the ultrasonic speaker 13 and the center of
the head M of the listener P represented as Q~ in Fig. 3 based
upon the time differences t1, t2 and the sound Velocity V.
The sound Velocity V may be preliminarily preset as a
constant in the distance calculating circuit 18 or alternatively
may be changed with changes in atmospheric temperature, humidity
l0
20~~3~8~
and atmospheric pressure and the like. On calculating the
distance ~, compensation may be conducted for the positional
relation between the signal detector 5L and 5R and the center of
the head M, the shape and size of the hand M.
Signals representative of the distance ~0, time differences
t~ and t2 are fed to an angle calculating circuit 20.
The circuit 19 for detecting the time difference between
both ears detects the time difference t3 between the pulse
signals generated by the fi rst and second edge detecting ci rcuits
15 and 16, represented as D3 in Fig. 2. A signal representative
of the time difference t3 is fed to the angle cal cu lat ing ci rcuit
20.
The angle calculating circuit 20 calculates an angle
representative of the direction of the head M represented by an
arrow 6~ in Fig. 3 by using the time differences t~, t2, t3, the
distance Q~, the sound velocity V and the radius r of the head M.
The angle 80 can be determined, for example, by the equation 1 as
follows:
B o = S 1 n '' ( V Z ( t , ~ C z) t a / 4 r 2 } . . . . ( 1 )
Then, the rotation angle 8 of the head M relative to a. desired
position of a virtual sound source is calculated from information
on the angle 0~ and the distance Q~ representative of the
relative positional relationship between a reference position and
the listener P by assuming that the position of the ultrasonic
11
~~~~~~'~i
speaker 13 be the reference position of the vi rtual sound source.
Information on the rotation angle of the head of the
listener obtained by the angle calculating circuit 20 is
provided to a control circuit 21.
In the audio signal reproducing apparatus of t.h;~
embodiment, the operation unit 14 includes a storing circuit 22
in which information on transfer characteristics from the virtual
sound source to both ears of the listener in at least the first
quadrant of the rotational angular position of the head of the
listener, for example, information on the transfer
characteristics for each angle 8~~ to 8~n in the first quadrant.
Based upon the current angle position calculated by the
angle calculating circuit 20, the control circuit 21 reads the
information on the transfer characteristics corresponding to the
current angles e» to 8~~ positions from the storing circuit 22 if
the current angle position is in the first quadrant in Fig. 4 and
reads the transfer characteristics information in which the
current angles 62~ to 82~ corresponds to the angles A~~ to 0~~ in
the first quadrant from the storing circuit 22 if the current
angle position is in the second quadrant in Fig. 4 and read the
transfer characteristics information in which the current angles
631 to 83n corresponds to the angles 611 to 8~~ in the first
quadrant from the storing circuit 22 if the current angle
position is in the third quadrant in Fig. 4 and read the transfer
characteristics informat ion in which the current angles 641 to
12
~~~~~~~
64~ correspond to the angles 8~~ to 8~~ in the first quadrant from
the storing circuit 22 if the current angle position is in the
fourth quadrant in Fig. 4 and supplies the read transfer
characteristics information to an audio signal processing ci rcuit
23 together with a signal representative of the quadrant in which
the current angular position is located.
Since the head of the listener is substantially spherical
and rotary symmetric, the transfer characteristics from the
virtual sound sources to both ears of the listener can be treated
as symmetrical in each quadrant.
Alternatively, in the control circuit 21, two transfer
characteristics in the vicinity of the rotational angular
position of the head represented by the angular position
information may be read form the storing circuit 22 and the
information on the transfer characteristics in the current head
rotational angular position may be operated by, for example,
linear interpolation processing.
Left and right channel audio signals S~ and SR which are
outputted from the audio signal source 22 are supplied to the
audio signal processing circuit 23.
The audio signal source 24 is an apparatus for outputting
given left and right channel audio signals S~ arid SP, such as
recording disc playback apparatus or radio communication
receivers and the like.
The audio signal processing circuit 23 performs a signal
13
processing which provides the left and right channel audio
signals S~ and SR fed from -the audio signal source 24 w;th a
given transfer characteristics form the virtual sound source to
the both ears of the listener. The audio signal processing
circuit 23 comprises first to sixth switches 25L, 25R, 26L. 26R,
27L and, 27R for switching the signal lines and first to fourth
signal processing units 28a, 28b, 28c and 28d.
The first to sixth switches 25L, 25R, 26L, 26R, 27L and 27R
are controlled for switching in response to a control signal from
the control circuit 21 representative of the quadrant to which
the current angular position belongs.
The first and second switches 25L and 25R perform switching
of i nputs of 1 eft and ri ght channel audi o si gnal s S~ and SR fed
from the audio signal source 24 and supply the right channel
audio signal SR to the first and second signal processing units
28a and 28b and suppl y the 1 eft channel audi o si gnal S~ to the
third and fourth signal processing units 28c and 28d when the
current angular position is in the first or third quadrant and
supply the left channel audio signal S~ to the first and second
signal processing unit 28a and 28b and supply the right channel
audio signal SR to the third and fourth signal processing units
28c and 28d when the current angular position is in the second
or fourth quadrant.
The third and fourth switches 26L and 26R perform switching
of the output of the left and right channel audio signals E~ and
14
ER outputted from the audio signal processing circuit 23 and
select as a right channel audio signal ER the output signal of
the first adder 29R for adding the output signals of the first
and third signal processing unit 28a and 28c and select as a left
channel audio signal E~ the output signal of the second adder 29~
for adding the output signals of -the second and fourth signal
processing units 28b and 28d when the current angular position
is in the first or third quadrant and select as a right channel
audio signal ER the output signal of the first adder 29L and
select as a left channel audio signal E~ the output signal of the
second adder 29L when the current angular position is in the
second or the fourth quadrant.
The third and fourth switches 26~ and 26R perform switching
of filters for the left and right channel audio signals E~ and ER
outputted from the audio signal processing circuit 23 and output
the left and right audio signals E~ and ER unswitched when the
current angular position is in the second or fourth quadrant and
output the Audi o si gnal s E~ and ER f rom whi ch hi gh f requency
components have been removed by low pass filters 30L and 30R
when the current angular position is in the second or fourth
quadrant.
In each of signal processing units 28a, 28b, 28c and 28d,
an impulse response representative of the transfer
characteristics of the left and right channeO audio signals S~
and SR reproduced from a.pair of left and right channel speakers
which are virtual sound sources facing to a listener to each ear
of the listener is preset based upon information on transfer
characteristics supplied from the control circuit 21.
In other words, the first signal processing unit 28a presets
the impulse response {hRR(t, e)} representative of transfer
characteristics of the sound reproduced from the right channel
audio signal SR to the right ear. The second signal processing
unit 28b presets the impulse response {hR~(t, 9)}
representative of the transfer characteristics of the sound
reproduced from the right channel audio signal SR to the left
ear. The third signal processing unit 28c presets the impulse
response {h~R(t, 8)} representative of transfer characteristics
of the sound reproduced form the left channel audio signal S~ to
the right ear. The fourth signal processing unit 28d presents
the impulse response {h~~(t, 8)} representative of the transfer
characteristics of the sound reproduced from the left channel
audio signal S~ to the left ear.
When the current angular position of the head of the
listener is in the first quadrant, the right channel audio signal
SR is fed the first and second signal processing units 28a and
28b. In the first signal processing unit 28a, the right channel
audio signal SR is subjected to a signal processing of
convolution-integration of the impulse response {hRR(t, 8)}. In
the second signal processing unit 28b, the right channel audio
signal SR is subjected to a signal processing of convolution-
16
integration of the impulse response {hR~(t, e)}.
The left channel audio signal S~ is fed to the third and
fourth signal processing units 28c and 28d. In the third signal
processing unit 28c, the left channel audio signal S~ is
subjected to a signal processing of convolution-integration of
the impulse response {h~R(t, 8)}. In the second signal
processing unit 28d, the left channel audio signal S~ is
subjected to a signal processing of convolution-integration of
the impulse response {h~~(t, 8)}.
The output signals from the first and third signal
processing units 28a and 28c are applied to the right channel
adder 29R and are added with each other therein. The output
signal of the right channel adder 28R is fed as the right channel
studio signal ER via the right channel amplifier 31R to the right
channel headphone 2R and reproduced as a sound. The output
signals from the second and fourth signal processing units 28b
and 28d are applied to the left channel adder 29L and are added
with each other therein. The output signal of the left channel
adder 29 is fed as the left channel audio signal E~ via the left
channel amplifier 31L to the left channel headphone 2L and
reproduced as a sound.
When the current angular position of the head of the
'listener is in the second quadrant, the left and right channels
of inputs and outputs are replaced with each other and a
processing which is similar to that of the foregoing first
1 '7
:~~48~~~
quadrant is performed. Accordingly, a front localization
sensation is provided. When the current angular position of the
head of the listener is in the third and fourth quadrants a
processing which is similar to those of the first and second
quadrants is performed. Audio signals E~ and ER from which high
f requency components have been removed f rom the 1 ow pass f i 1 to rs
30L and 30R are outputted. Accordingly, rear localization
sensation can be provided.
In the audio signal reproducing apparatus of the thus formed
embodirnent, information on the transfer characteristics in the
rotational angular positions corresponding to the movement of the
head of the listener calculated by the angle calculating circuit
20 is formed based upon the information upon the transfer
characteristics of the first quadrant stored in the storing
circuit 22. By performing a signal processing of the left and
right channel audio signals S~ and SR which responds to changes
in transfer characteristics in association with the movement of
the listener P and the rotation of the head M in real time in the
audio signal processing circuit 23 based upon the transfer
characteristics data, good outside head localization sensation
and front localization sensation are obtained in which the
virtual sound sources are not moved as similarily to the case in
which an audio signal is reproduced by a pair of speaker systems
S~ and SR which faces to the listener P and are remote therefrom
and with each other as is shown in Figs. 5A, 5B and 5C in which
18
relative positional relations between the virtual sound sources
and the listener P are illustrated.
Fig. 5B shows that the listener P has approached to a pair
of speaker systems S~ and SR, that is, virtual sound sources from
a position of Fig. 5A. Fig. -0C shows that the listener P rotates
his head M toward the right speaker device SR. By performing a
signal processing which can respond in real time to changes in
transfer characteristics in association with the movement of the
listener and the rotation of the head M as mentioned above in the
audio signal reproduction apparatus of the present embodiment,
good head outside and front localization sensation in which no
virtual sound source is moved can be obtained so that a binaural
reproduction which can respond to any conditions of Figs. 5A, 5B
and 5C can be performed.
Since it suffices for the audio signal reproducing apparatus
of the present invention to store in storing means transfer
characteristics information representative of the transfer
characteristics from virtual sound sources to a listener of at
least the first guadrant of the rotational angular position of
the head of the listener, the amount of the information of the
transfer characteristics to be stored in the storing means is
small and the storing means having a low storing capacity can be
used. The audio signal processing means farms the transfer
characteristics information in the rotational angular position
represented by a detection output from detecting means for
19
detecting the rotational angular position depending upon the
movement of the head of the listener in accordance with the
transfer characteristics information of at least the first
quadrant stored in the storing means and processes the left and
right channel audio signals for supplying the processed audio
signals to the headphone set. Accordingly, a proper binaural
reproduction can be performed for providing a very natural sound
image localization sensation in which the positions of the
virtual sound sources are not moved even if the listener moves.
A second embodiment of an audio signal reproducing apparatus
of the present invention will now be described in detail with
reference to the drawings.
The audio signal reproducing apparatus of the present
invention shown in Fig. 6 comprises a headphone set 40 which is
fitted over the head M of a listener P and a pair of headphones
42L and 42R are supported by a head band 41 so that they are
located in the vicinity of left and right ears of the listener
P, as is similar to the embodiment shown in Fig. 1.
'fwo sliders 44L and 44R from which support arms 43L and 43R,
respectively project are slidably mounted on the head 1 of the
headphone set 40. A pair of signal detectors 45L and 45R which
detect a position detection reference signal emitted from a
reference signal source 51 are provided at the tip ends of -the
support arms 43L and 43R, respectively. That is, the pair of
signal detectors 45L and,45R are provided on the tip ends of the
~~4~~~~
support arms 43L and 43R projectedly formed on the sliders 44L
and 44R which are slidably mounted on the head band 51 so that
they are supported in positions remote from the head band 51 and
the pair of headphones 42L and 42R, that is the main body of the
headphone set.
Also in this present embodiment, the reference signal source
51 comprises an ultrasonic signal source 52 and an ultrasonic
speaker 53 for generating an ultrasonic signal from the
ultrasonic signal source 52 as a reference signal. Each of the
pai r of signal detectors 45L and 45R which receives the reference
signal comprises an ultrasonic microphone.
An ultrasonic wave generated from the ultrasonic speaker 53,
that is, the position detection reference signal is a burst wave
in which an ultrasonic wave having a given level is
intermittently generated for a given period of time as is similar
to the f i rst embod i ment , o r an a 1 t rason i c wave , the phase of
which may be detected like a so-called level modulated wave, the
level of which changes in a given circle.
The pair of signal detectors 45L and 45R provided on the
headphone set 40 detects the ultrasonic position detection
reference signal generated from the ultrasonic speaker 53 and
generate respective detection signals, each having a time lag
depending upon the relative positional relation between the
listener P and the ultrasonic speaker 53.
Each detection signal obtained by these signal detectors 45L
21
and 45R is applied to an operation unit 54.
The operation unit 54 comprises first and second edge
detecting circuit 55 and 56, to which the detection signal from
the signal detectors 45L and 45R for detecting the position
detection reference signal are supplied, respectively and a third
edge detecting circuit 57 to which an ultrasonic signal from the
ultrasonic signal source 52, that is, the position detection
reference signal is applied.
The first and second edge detecting circuits 55 and 56
detect rise-up edges of the detection signals generated from the
signal detectors 45L and 45R, respectively and output pulse
signals corresponding to the rise-up edges pulse signals
generated by the first and second edge detecting circuits 55 and
56 are supplied to a distance calculating circuit 58 and a
circuit 59 for detecting the time difference between both ears.
The third edge detecting circuit 57 detects the rise-up edge of
the ultrasonic signal from the ultrasonic signal source 52 and
outputs a pulse signal corresponding to the rise-up edge. A
pulse signal obtained by the third edge detection circuit 57 is
supplied to the distance calculating circuit 58.
The distance calculating circuit 58 detects the time
difference t~ between pulse signals obtained by the thi rd and
first edge detecting circuits 57 and 55 and the time difference
tZ between pulse signals obtained by the third and second edge
detecting circuits 57 and 56 and then calculates the distance PD
22
between the ultrasonic speaker 53 and the center of the head M
of the listener based upon the time differences t~, t2 and the
sound velocity V.
Signals representative of the distance Q0, time differences
t~ and t2 are fed to an angle calculating circuit 60.
The ci rcuit 59 for detecting the time difference between
both ears detects the time difference t3 between the pulse
signals generated by the first and second edge detecting circuits
55 and 56. A signal representative of the time difference t3
is fed to the angle calculating circuit 60.
The angle calculating circuit 60 calculates an angle 8~
representative of the direction of the head M by using the time
differences t~, t2, t3, the distance t~~, the sound velocity V and
the radius r of the head M similarly to the angle calculating
circuit 20 in the first embodiment.
Information on the rotation angular position head of the
listener obtained by the angle calculating circuit 60 is provided
to an interpolation operation and processing circuit 61.
In the audio signal reproducing apparatus of the present
embodiment, the operation unit 54 includes a storing circuit 62
in which transfer characteristics information representative of
the transfer characteristics from the virtual sound sources to
both ears of the listener for each predetermined angle, which is
larger than that of the angular positional information of the
listener calculated by the angle calculating circuit 60.
23
The interpolation operation and processing circuit 61 reads
the information on two transfer characteristics in the vicinity
of the rotational angular position of the head represented the
current angular positional information calculated by the angle
calculating circuit 60 and operates the transfer characteristics
in the current rotational angular position of the head by, for
example, a linear interpolation processing.
The interpolation operation and processing circuit 61 may
reads the information on more than two transfer characteristics
in the vicinity of the current rotational angular position of the
head represented by the angular positional information for
performing secondary interpolation processing other than the
linear interpolation processing.
The information on the transfer characteristics in the
current rotational angular position obtained by the interpolation
operation and processing circuit 61 is supplied to an audio
signal processing circuit 63.
The audio signal processing circuit 63 is also supplied with
left and right channel audio signals S~ and SR outputted from an
audio signal source 64.
The audio signal source 64 is a device for outputting
predetermined left and right channel audio signals S~ and SR and
may includes, for example, various recording disc playback
devices, recording the playback device of wireless receivers and
the like.
24
2~~4~~~~i
The audio signal processing circuit 63 performs a signal
processing which provides the left and right channel audio
signals S~ and SR fed from the audio signal source 64 with a
given transfer characteristics from the virtual sound source to
the both ears of the listener. The audio signal processing
circuit 63 comprises first through fourth signal processing units
65a, 65b, 65c and 65d to which the transfer characteristics
information in the current rotational angular positional of the
head obtained by the interpolation operation and processing
circuit 61. In each of signal processing units 65a, 65b, 65c and
65d, an impulse response representative of the transfer
characteristics of the left and right channel audio signals S~
and SR reproduced from a pair of left and right channel speakers
which are virtual sound sources facing to a listener to each ear
of the listener is preset based upon information on transfer
characteristics.
In other words, the first signal processing unit 65a
presents the impulse response {hRR(t, e)} representative of the
transfer characteristics of the sound reproduced form the right
channel audio signal SR to the right ear. The second signal
processing unit 65b presets the impulse response {h~~(t, 6)}
representative of the transfer characteristics of the sound
reproduced from the right channel audio signal SR to the left
ear. The third signal processing unit 65c presets the impulse
response {h~R(t, 0)}. representative of the transfer
characteristics of the sound reproduced from the left channel
audio signal S~ to the right ear. The fourth signal processing
unit 65d presets the impulse response {h~~(t, 8)} representative
of the transfer characteristics of the sound reproduced from the
left channel audio signal S~ to the left ear. In the audio signal
processing circuit 63, the right channel audio signal S~ is fed
the first and second signal processing units 65a and 65n. In the
first signal processing unit 65a, the right channel audio signal
S~ is subjected to a signal processing of convolution-integration
of the impulse response {hRR(t, e)}. In the second signal
processing unit 65b, the right channel audio signal SR is
subjected to a signal processing of convolution-integration of
the impulse response {hR~(t, A)}.
The left channel audio signal S~ is fed to the third and
fourth signal processing units 65c and 65d. In the third signal
processing unit 65c, the left channel audio signal S~ is
subjected to a signal processing of convolution-integration of
the impulse response {h~R(t, e)}. In the second signal
processing unit 65d, the left channel audio signal S is
subjected to a signal processing of convolution-integration of
the impulse response {h~~(t, e)}.
The output signals from the first and third signal
processing units 65a and 65c are applied to the right channel
adder 66R and are added with each other therein. The output
signal of the right channel adder 66R is fed as the right channel
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audio signal ER via the right channel amplifier 68R to the right
channel headphone 4R of the headphones 40 and reproduced as a
sound. The output signals from the second and fourth signal
processing units 64b and 64a are applied to the left channel
adder 66L and are added with each other therein. The output
signal of the right channel adder 66L is fed as the left channel
audio signal ER via the left channel amplifier 68L to the left
channel headphone 42L of the headphone set 40 and reproduced as
a sound.
:Ln the thus formed audio signal reproducing apparatus of
this embodiment, information on two transfer characteristics in
the vicinity of the rotational angular position represented by
the current angular positional information is read from the
storing circuit 62 based upon the current angular positional
'information calculated by the angle calculating circuit 60. The
transfer characteristics information in the current rotational
angular position are operated by a linear interpolation
processing in the interpolation operation circuit 61. By
performing a signal processing which responds to changes 'in
transfer characteristics in association with the movement of the
listener and the rotation of the head M in real time in the audio
signal processing circuit 63 based upon the transfer ~'
characteristics data, good outside head localization sensation
and front localization sensation are obtained in which the
virtual sound sources are not moved as similarly to the case in
27
~~~~~a~~i
which an audio signal is reproduced by a pair of speaker systems
which faces to the listener and are remote therefrom and with
each other.
As mentioned above, in the audio signal reproducing
apparatus of the present invention, information on at least two
transfer characteristics in the vicinity of the rotational
angular position of the head represented by the detection output
from detecting means for detecting the rotational angular
position of the head of the listener at a solution higher than
that of the transfer characteristics information stored in the
storing means is read from the storing means. The transfer
characteristics information in the rotational angular position
of the head represented by the detection output are
interpolation-operated by interpolation operation means.
Accordingly, the amount of the information on the transfer
characteristics stored in the storing means can be reduced. The
audio signal processing means processes the left and right
channel audio signals based upon the transfer characteristics
information determined by the interpolation operation means. The
processed audio signals are supplied to the headphones, resulting
in that a proper binaural reproduction can be achieved for
providing very natural sound image localization sensation in
which the positions of the virtual sound sources do not move even
if a listener moves.
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