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JP2004166212

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DESCRIPTION JP2004166212
PROBLEM TO BE SOLVED: To localize a sound image out of the head with less signal processing.
SOLUTION: The level of an input acoustic signal on the left is adjusted, the level of a left
reflection sound signal 5 on which the frequency characteristic of reflection by a wall is given to
the input acoustic signal on the left, and the level of the input acoustic signal on the right are
adjusted A signal obtained by adding the left reflected sound signal 21 obtained by adding the
frequency characteristic of reflection by the wall to the delayed signal and the right input
acoustic signal, and a signal obtained by adding the frequency characteristic indicating the
difference between both ears are added Let the left output signal to the headphones. The right
output signal to the headphones is obtained in the same way. [Selected figure] Figure 1
Headphone playback method and apparatus
The present invention relates to a headphone reproduction method and apparatus using digital
signal processing in the acoustic field, and in particular, the human auditory sense characteristic
and the sound of a room by minimum necessary delay processing and filter processing, etc. The
present invention relates to a headphone reproduction method and apparatus which reproduces
a speaker image and mounts an equalizer so as to generate a sense of localization outside the
head of a sound image without losing the sound quality of the original sound. [0002] A
conventional headphone device synthesizes a direct sound and a reflected sound that are
transmitted to the right and left ears of a listener from a speaker placed in a virtual space,
thereby generating a sound image The localization is simulated with headphones. The sound that
reaches the left and right ears from the speaker directly or through reflections in the wall or
ceiling of the room has separate transfer characteristics on the left and right, so in signal
processing by DSP etc. these transfer characteristics are input signals as transfer functions on the
left and right And reproduce the localization of the sound image in a pseudo manner. FIG. 6 is a
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block diagram of a headphone reproduction apparatus that generates a sense of direction
(transfer function) of a sound source and localizes a sound image outside the head by small-scale
hardware. In this technology, a single-channel input audio signal is branched into a left channel
signal and a right channel signal, and delay processing (delay unit), transfer function correction
processing (low pass filter), and volume correction processing (multiplier) are respectively
performed on both signals. By applying the virtual sound source, an acoustic signal transmitted
from the virtual sound source to the left ear and the right ear of the listener is generated. The
transfer function correction process is a process of convoluting a filter for synthesizing different
frequency elements according to the direction of arrival of sound (see, for example, Patent
Document 1). In FIG. 6, reference numerals 33 and 34 denote delay devices, reference numerals
43 and 44 denote low pass filters, and reference numerals 53 and 54 denote multipliers. By
processing the input sound signal input to the input terminal 31, Simulates the direct sound to
the left and right ears. The reflected sound generates a plurality of reflected sounds by the delay
unit 32 and is then subjected to different delay processing (delay units 35 to 42) according to the
direction of arrival of each reflected sound, transfer function correction processing (low pass
filter 45 To 52), volume correction processing (multipliers 55 to 62) is applied, and the output
signals of the multipliers 53 and 54 are separately added and synthesized by the adders 63 to 70
separately. As described above, the direct sound and the reflected sound of the left ear and the
right ear are added by the adders 63 to 70 and sent to the left channel and the right channel of
the headphone, thereby virtually reproducing the localization of the sound image by the speaker
with the headphone It is
[Patent Document 1] JP-A-8-237790. SUMMARY OF THE INVENTION However, in the abovedescribed prior art, since the transfer function for generating the sense of direction not only to
the reflected sound but also to the direct sound is added, the sound quality difference with the
original sound is obtained. The problem is that the In addition, the delay processing for
generating sense of direction for each reflected sound, the transfer function correction
processing, and the volume correction processing are separately performed, so that the amount
of signal processing increases as the number of reflected sounds increases. Furthermore, if the
number of reflected sounds is reduced to reduce the amount of signal processing in the DSP,
there is a problem that the frequency characteristics of reflection by the wall of the listening
room can not be sufficiently reproduced. The present invention has been made in view of the
above problems, and an object thereof is to improve the reproducibility of the sound of a
listening room with a small number of reflected sounds and to localize a sound image outside the
head with a small amount of signal processing. It is an object of the present invention to provide
a headphone reproduction method and apparatus which are capable of further improving the
sound quality of the original sound. The invention according to claim 1 is a headphone
reproduction method for processing left and right input sound signals and realizing localization
of a sound image by a speaker in a pseudo manner by stereo headphones, the left input The first
left reflected sound signal obtained by adjusting the level of the sound signal, the left input sound
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signal with the frequency characteristic of reflection by the wall, and the delay processing and
level adjustment, and the right input sound signal are delayed. The frequency characteristic of
the reflection by the wall is added to the level adjusted signal and the right input acoustic signal,
and the second left reflected sound signal subjected to the delay processing and the level
adjustment is added, and then the frequency indicating the difference between both ears A signal
obtained by adding the left signal to which the characteristic is added is used as a left output
signal to the headphone, and the signal whose level of the right input acoustic signal is adjusted,
and the frequency characteristic of the reflection by the wall to the right input acoustic signal.
The first right reflected sound signal subjected to delay processing and level adjustment, and the
signal whose level is adjusted by delaying the left input acoustic signal and the left input acoustic
signal are given frequency characteristics of reflection by the wall. A right output signal to the
headphone is obtained by adding a second right reflected sound signal subjected to delay
processing and level adjustment, and then adding a right signal to which a frequency
characteristic indicating the difference between both ears is added. The headphone reproduction
method is characterized by According to a second aspect of the present invention, in the
headphone reproduction method according to the first aspect, the signal in which the level of the
left input acoustic signal is adjusted, the first left reflected sound signal, and the frequency
characteristic are provided. A signal obtained by adding the added signal for the left and
subjected to an equalizer process as an output signal for the left of the headphone and adjusting
the level of the input acoustic signal for the right, and the first right reflected sound signal The
headphone reproduction method is characterized in that the signal subjected to the equalizer
processing after adding the signal for the right to which the frequency characteristic is given is
added as the output signal for the right of the headphone.
According to a third aspect of the present invention, there is provided a headphone reproduction
method for processing left and right input sound signals and realizing localization of a sound
image by a speaker in a pseudo manner with stereo headphones, the signal having the level of
the left input sound signal adjusted. A first left reflected sound signal obtained by adding a
frequency characteristic of reflection by a wall to the left input acoustic signal and performing
delay processing and level adjustment; a signal obtained by delaying the level of the right input
acoustic signal; Delay processing and level are given to the left input sound signal and the left
input sound signal to which the frequency characteristic of reflection by the wall is added to the
right input sound signal and the delay processing and level adjustment are given to the delay
processing and level After adding the adjusted third left reflected sound signal, the left signal to
which the frequency characteristic indicating the difference between both ears is added and the
frequency characteristic of reflection by the wall are added to the right input acoustic signal. A
signal obtained by adding the fourth left reflected sound signal subjected to delay processing and
level adjustment to the left output signal to the headphone and adjusting the level of the right
input sound signal, and the right input sound signal The first right-reflected sound signal to
which the frequency characteristic of the reflection by the wall has been applied and to which the
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delay processing and the level adjustment are applied, and the signal whose level is adjusted by
delaying the level of the left input acoustic signal and the wall Frequency characteristic of
reflection by the wall and delay processing and level adjustment with the second right reflection
sound signal and the right input acoustic signal by adding frequency characteristic of reflection
by the wall and delay processing and level adjustment The right signal to which the frequency
characteristic indicating the difference between both ears has been added after adding the right
reflection sound signal, and the frequency characteristic of reflection by the wall to the left input
acoustic signal are subjected to delay processing and level adjustment 4 right reflected sound
signals, The sum signal and the right output signal to the headphone, and the headphone
reproducing method characterized by. According to a fourth aspect of the present invention, in
the headphone reproduction method according to the third aspect, the signal in which the level
of the left input sound signal is adjusted, the first left reflected sound signal, and the frequency
characteristic are provided. A signal obtained by adding an applied left signal and the fourth left
reflected sound signal and performing an equalizer process as a left output signal of the
headphone and adjusting the level of the right input acoustic signal, A signal obtained by adding
the first right reflected sound signal, the right signal to which the frequency characteristic has
been added, and the fourth right reflected sound signal and then applying an equalizer process to
the right output signal of the headphone The headphone reproduction method is characterized in
that. According to the fifth aspect of the present invention, in the headphone reproduction
apparatus which processes left and right input sound signals and virtually localizes a sound
image by a speaker with stereo headphones, the levels of the left and right input sound signals
are respectively adjusted. Filter the reflection by the wall to the 1st and 2nd sound pressure
adjustment means, the 1st and 2nd delay multiplication means which respectively delay the left
and right input sound signal to adjust the level, and the left and right input sound signal The first
left reflected sound signal and the second right reflected sound signal are subjected to delay
processing and level adjustment by inputting the first and second frequency characteristic
generation filters to be applied and the output signal of the first frequency characteristic
generation filter First reflected sound generation means for generating the first output signal of
the second frequency characteristic generation filter to perform delay processing and level
adjustment; Second reflected sound generation means for generating a second left reflected
sound signal; first addition means for adding an output signal of the second delayed
multiplication means and the second left reflected sound signal; A second addition means for
adding the output signal of the first delay multiplication means and the second right reflected
sound signal, and a frequency characteristic for indicating the difference between the two ears to
the output signal of the first addition means A first low-pass filter, a second low-pass filter for
giving a frequency characteristic indicating a difference between both ears to an output signal of
the second addition means, an output signal of the first sound pressure adjustment means, the
first Third adding means for adding the left reflected sound signal of the first low pass filter and
the output signal of the first low pass filter, the output signal of the second sound pressure
adjusting means, the first right reflected sound signal, and And fourth addition means for adding
the output signals of the two low-pass filters And a headphone reproducing apparatus which is
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characterized in that the left and right output signals to the third and fourth, respectively
headphone output signal of the adding means.
The invention according to claim 6 is the headphone reproduction apparatus according to claim
5, wherein the first reflected sound generation means further receives an output signal of the
first frequency characteristic generation filter and performs delay processing And level
adjustment to generate a third left reflected sound signal and a fourth right reflected sound
signal, and the second reflected sound generation means further receives an output signal of the
second frequency characteristic generation filter Delay processing and level adjustment to
generate a third right reflected sound signal and a fourth left reflected sound signal, and the first
addition means further adds the third left reflected sound signal The second addition means
further adds the third right reflection sound signal, the third addition means further adds the
fourth left reflection sound signal, and the fourth addition means , Further adding the fourth
right reflected sound signal, The headphone reproduction apparatus is characterized by A
seventh aspect of the present invention is the headphone reproduction apparatus according to
the fifth or sixth aspect, comprising: a first equalizer filter that receives an output signal of the
third addition means and performs sound quality correction; And a second equalizer filter for
performing sound quality correction by inputting the output signal of the adding means of No. 4;
and the output signals of the first and second equalizer filter means are respectively the left and
right output signals to the headphones The headphone reproducing apparatus is characterized in
that According to an eighth aspect of the present invention, in the headphone reproduction
device according to the fifth aspect, the first and second frequency characteristic generation
filters, the first and second low pass filters, and the first and second low pass filters. A headphone
reproduction apparatus is characterized in that the first and second equalizer filters are IIR type
filters. The invention according to claim 9 is the headphone reproduction apparatus according to
claim 8, wherein the first and second frequency characteristic generation filters and the first and
second low pass filters are first-order IIR type low pass The headphone reproducing apparatus is
characterized in that it comprises a filter, and the first and second equalizer filters comprise a
shelving type 1st order IIR high pass filter. BEST MODE FOR CARRYING OUT THE INVENTION In
the present invention, a transfer function (frequency characteristic) indicating the difference
between both ears is given to one sound reaching the left and right ears (the transfer function of
one arrival sound is 1 The processing of the low-pass filter is reduced by configuring the transfer
function of the other arrival sound as the transfer function of the difference between the two ears
that indicates the difference between the transfer functions of both arrival sounds, thereby
reducing the amount of signal processing. Reduce
The transfer function indicating the difference between the two ears in this filtering process is
equivalent to the case of combining the transfer functions of the arrival sounds to the left and
right ears, and does not reduce the effect of the out-of-head localization of the sound image.
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Further, since the frequency characteristics of the direct sound from the ear close to the sound
source do not change, the difference in sound quality with the original sound can be minimized.
Also, transfer functions indicating the difference between the two ears are not prepared
separately depending on the direction of arrival of the sound (such as forward or backward) and
are common, and a plurality of signals are added to form a single signal. By providing the
transfer function shown, the amount of signal processing is reduced. In addition, frequency
characteristic generation filter processing is applied to the input acoustic signal, and then
different delay processing is performed to generate a plurality of reflected sounds, so that the
frequency characteristics when the reflected sound is reflected on the wall one by one. By
increasing the number of reflections, it is possible to improve the reproducibility of the sense of
the spaciousness and sound of the listening room. Further, assuming that the wall of a virtual
room is a porous sound absorbing material suitable for hearing, a first-order IIR low-pass filter in
which the first and second frequency characteristic generation filters are attenuated gently in the
high region The amount of signal processing is reduced by simulating with. Furthermore, the
amount of signal processing is reduced by simulating the first and second low-pass filters that
generate transfer functions indicating the difference between both ears with a first-order IIR lowpass filter. Furthermore, by applying the equalizer processing for sound quality correction to the
left and right output signals of the headphone, an unpleasant sound quality difference with the
original sound is eliminated, and the equalizer processing for sound quality correction is made a
shelving type 1st order IIR high pass filter. Therefore, the filtering process here is also greatly
reduced to reduce the amount of signal processing. First Embodiment FIG. 1 is a block diagram of
a headphone reproduction apparatus according to a first embodiment of the present invention. In
FIG. 1, 1 and 14 are input terminals of left and right stereo sound signals, 2 and 15 are
multipliers (first and second sound pressure adjusting means) for adjusting the level (sound
pressure) of the input signal, 3 and 16 Is a filter circuit (first and second frequency characteristic
generation filters) for giving frequency characteristics of the reflected sound from the wall to the
input signal, and 4 and 17 are for dividing the input signal into a plurality of times. Reflected
sound generation circuit (first and second reflected sound generation means) for generating a
plurality of reflected sounds delayed in time and multiplied by a value to perform level
adjustment (5, 6, 7, 8, 18, 19, 20) , 21 is a reflected sound signal group in which a plurality of
reflected sounds generated by the reflected sound generation circuits 4 and 17 are respectively
combined without overlapping, and 1, second delay multiplication means), 10, 23, 12 25 is an
adder (first to fourth addition means), 11 and 24 are low pass filter circuits (first and second low
pass filters) for giving a transfer function indicating the difference between both ears to the
signal, 13, Reference numeral 26 is an output terminal for the left and right stereo sound signals.
Stereo sound signals are input to input terminals 1 and 14. The left channel signal (hereinafter
referred to as Lch) of the stereo signal is input to the input terminal 1, and the right channel
signal (hereinafter referred to as Rch) of the stereo signal is input to the input terminal 14. The
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Lch input signal is input to the multiplier 2 and the delay multiplication circuit 9, and the
multiplier 2 generates a direct sound that reaches the left ear from the left speaker placed in the
virtual room, and the delay multiplication circuit 9 generates the direct sound. A direct sound
reaching the right ear with a pressure difference and a time difference is generated relative to
the direct sound reaching the left ear. Similarly, the Rch input signal is also input to the multiplier
15 and the delay multiplication circuit 22, and the multiplier 15 generates a direct sound
reaching the right ear from the right speaker placed in a virtual room, and the delay
multiplication circuit 22 generates a direct sound reaching the left ear having a sound pressure
difference and a time difference with respect to the direct sound reaching the right ear. FIG. 2 is
an explanatory view of the arrival time difference of the direct sound from the right speaker to
the left and right ears. t1 represents a direct sound (arrival time t1) reaching the right ear closer
to the right speaker SR from the right speaker SR, and t2 a direct sound reaching the left ear
farther from the right speaker SR (arrival time t2) Indicates The arrival time difference Δt
between the left and right ears is given by Δt = t2−t1 . The delay processing portion of the
delay multiplication circuit 22 described above delays and adjusts the level of the Rch direct
sound signal by a time corresponding to the arrival time difference Δt. The delay processing
portion of the delay multiplication circuit 9 delays and level adjusts the Lch direct sound signal
by a time corresponding to the arrival time difference Δt. Also, the input signal is input to the
filter circuits 3 and 16 and given a frequency characteristic that occurs when sound strikes the
wall and is reflected. By varying the frequency characteristics of the filter circuits 3 and 16, it is
possible to simulate the frequency characteristics of the reflected sound according to the
material of the wall of the listening room. It is said that reflections of sounds that arrive at a short
time interval after the direct sound affect the spatial expanse of the room and the impression of
sound, and to give these reflections a frequency characteristic according to the material of the
wall In particular, when the number of reflected sounds is reduced, it contributes to enhancing
the reproducibility such as the feeling of expansion of the room. Here, if it is assumed that the
wall of the virtual room is a porous sound absorbing material suitable for hearing, the
characteristic that the high region is gently attenuated to absorb the high region is This can be
simulated by using a first-order IIR low-pass filter for 16 and the amount of signal processing can
be reduced.
If the filter circuits 3 and 16 are realized by a first-order IIR digital filter as described above, the
scale can be reduced. The outputs of the filter circuits 3 and 16 are input to the reflected sound
generation circuits 4 and 17, respectively, where a plurality of reflected sounds whose delay
amounts and levels are controlled are generated. FIG. 3 is an explanatory view of the reflected
sound generated in a virtual room provided with a wall that reflects the sound. t1 is a right direct
sound (arrival time t1) reaching the right ear from the right speaker SR, and t2 is a left direct
sound (arrival time t2) reaching the left ear far from the right speaker SR. R1 is a front right
reflected sound in which the sound of the right speaker SR comes from the right side of the
listener and reaches the right ear from the front, and R2 is the sound of the right speaker SR
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from the left of the listener and reaches the right ear from behind Back right reflection sound, R3
is the back left reflection sound when the sound of the right speaker SR comes from the left
direction of the listener and reaches the left ear from the back, R4 is the sound of the right
speaker SR comes from the right direction of the listener It is a front left reflection sound that
reaches the left ear from the front. The plurality of reflected sounds can be obtained by
simulating the above-mentioned state. At that time, the delay time of each of the reflected sounds
generated by the reflected sound generation circuits 4 and 17 is obtained as the base point (zero
second) of the delay time of the direct sound reaching the ear closer to the sound source from
the sound source. For example, the delay times of the reflected sounds R1 and R2 are values
obtained by subtracting the delay times of t1 from the respective delay times, and the delay times
of the reflected sounds R3 and R4 are obtained by subtracting the delay times of t2 from the
respective delay times. Value. By these, it is possible to accurately simulate the time to reach each
of the left and right ears for each reflected sound. The reflected sound generation circuit 17
corresponds to four reflected sound signal groups (corresponding to R1 to R4) with respect to
the position of the right speaker, the arrival direction of the reflected sound, and the ear for
reaching the reflected sound signal of the Rch branched and generated. ) Divide into 18 to 21
and output. 18 and 19 are right reflected sound signal groups (the first right reflected sound
signal group and the third right reflected sound signal group, respectively) reaching the right ear,
and 20 and 21 are left reflected sound signal groups (the first reflected sound signal group and
the third They are respectively the fourth left reflected sound signal group and the second left
reflected sound signal group). On the other hand, the reflected sound generation circuit 4 divides
the reflected sound signals of the Lch generated by branching into four reflected sound signal
groups 5 to 8 with respect to the position of the left speaker and the arrival direction of the
reflected sound and the ear to reach. Divide and output. 5 and 6 are left reflected sound signal
groups (the first left reflected sound signal group and the third left reflected sound signal group,
respectively) that reach the left ear, and 7 and 8 are right reflected sound signal groups that
reach the right ear ( They are respectively the fourth right reflected sound signal group and the
second right reflected sound signal group).
As described above, regarding the direct sound and the reflected sound in FIG. 3, in the circuit of
FIG. 1, the direct sound t 1 is a signal through the multiplier 15, the direct sound t 2 is the signal
through the delay multiplication circuit 22, The reflected sound R1 corresponds to the right
reflected sound signal group 18, the reflected sound R2 corresponds to the right reflected sound
signal group 19, the reflected sound R3 corresponds to the left reflected sound signal group 20,
and the reflected sound R4 corresponds to the left reflected sound signal group 21. The Rch
signal and the left reflected sound signal group 21 through the left reflected sound signal group
6 and the delay multiplication circuit 22 are added by the adder 10, and through the right
reflected sound signal group 19 and the delay multiplication circuit 9. The Lch signal and the
right reflection sound signal group 8 are added by the adder 23 and are input to low pass filter
circuits 11 and 24 which respectively add a transfer function indicating the difference between
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both ears. The characteristic of the transfer function indicating the difference between both ears
of the low-pass filters 11 and 24 is a characteristic obtained by convolving the inverse
characteristic of the transfer function of the ear near the sound source to the transfer function of
the ear far from the sound source Is a characteristic that simulates That is, for example, in FIG. 2
in the case of direct sound only, when the transfer function of the right direct sound t1 with a
short arrival time t1 is H1 and the transfer function of the left direct sound t2 with a long arrival
time t2 is H2, the right direct For the sound t1, the transfer function is 1 (the frequency
characteristic is flat), and for the left direct sound t2 only, the transfer function of the
characteristic of H2 × 1 / H1 which is the difference between both transfer functions (t1, t2
Transfer functions that indicate the difference between In the case of FIG. 3, the transfer function
is set to 1 for the reflected sound R3 having a short arrival time, and the transfer function
indicating the difference between the two ears of R2 and R3 is given for the reflected sound R2
having a long arrival time. Just do it. Further, the transfer function is set to 1 for the reflected
sound R1 having a short arrival time, and the transfer function indicating the difference between
both ears of R1 and R4 may be added to the reflected sound R4 having a long arrival time. FIG. 4
shows an example of the frequency characteristic of the transfer function (the frequency
characteristic of the low pass filters 11 and 24) showing the difference between both ears (the
above-mentioned H2 × 1 / H1 ). Since the transfer characteristics from the sound source to
the ear are large individual differences, even if the characteristics of the transfer function of a
specific human or a modeled dummy head are strictly simulated, the sound image localization
effect varies among individuals. Therefore, the signal processing is reduced by simulating the
transfer function indicating the difference between both ears with a simple low pass filter
without simulating the exact characteristics here. If the low pass filters 11 and 24 are realized by
a first-order IIR digital filter, the scale becomes smaller.
When the transfer function is simulated with a simple low-pass filter, the clues of the subtle
sound source arrival direction are already vague, and it makes sense to prepare a filter for each
signal in the sound arrival direction. It is possible to share the filter on the signal in the incoming
direction and apply the filter of the same characteristic. Therefore, as described above, in the
present embodiment, as a method of giving the arrival sound a frequency characteristic, the
direct sound signal passes through the multipliers 2 and 15 as it is, the left reflected sound signal
group 5 and the left reflected sound The signal group 20, the right reflected sound signal group
18, and the right reflected sound signal group 7 are also output as they are, except for that, one
low pass filter circuit 11 is used on the left, and one low pass filter circuit 24 is used on the right.
doing. The output signal of the low pass filter 11 is added to the left direct sound signal passed
through the multiplier 2, the front left reflection sound signal group 5 and the rear left reflection
sound signal group 20 in the adder 12, and sent to the output terminal 13. Be The output signal
of the low pass filter 24 is added to the right direct sound signal, the front right reflection sound
signal group 18 and the rear right reflection sound signal group 7 which have passed through
the multiplier 15 in the adder 25, and is sent to the output terminal 26. From the above,
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according to the first embodiment, it is possible to provide a headphone reproduction device that
can reduce the processing amount of the entire signal processing without reducing the effect of
sound source localization outside the sound source, and can be realized with a small scale DSP.
Second Embodiment FIG. 5 is a block diagram of a headphone reproduction apparatus according
to a second embodiment. The same components as those shown in FIG. 1 are designated by the
same reference numerals, and the detailed description thereof is omitted. In this embodiment, a
high-pass filter circuit 27 (first equalizer filter) for sound quality correction is inserted between
the adder 12 and the output terminal 13 on the Lch side, and the adder 25 and the output
terminal 26 on the Rch side. A high pass filter circuit 28 (second equalizer filter) for sound
quality correction is inserted between them. In the first embodiment described above, since the
low-pass filter circuits 11 and 24 are included, the user may feel slightly at a hearing and may
feel uncomfortable. Therefore, in the second embodiment, the above-mentioned sound quality is
corrected by inserting the above-described high-pass filter circuits 27 and 28 to maintain the
sound quality of the original sound. Here, by using a shelving type first-order IIR high-pass filter
circuit as the high-pass filter circuits 27 and 28, the amount of signal processing can be reduced.
From the above, in the second embodiment, the processing amount of the entire signal
processing can be reduced without deteriorating the sound quality of the sound source without
reducing the effect of the sound source localization outside the sound source, and can be realized
by a small scale DSP It is possible to provide a comfortable headphone reproduction device.
[Other Embodiments] In the embodiment described above, the reflected sound signal groups 6, 7,
19 and 20 arriving from the rear are also generated, but these can be omitted for simplification.
As described above, according to the present invention, since a plurality of reflection sound
signals are generated after the frequency characteristic of reflection on the wall is added to the
input signal, it is possible to set one reflection sound one by one. It is possible to give the
frequency characteristic when it is reflected on the wall, and it is possible to improve the
reproducibility of the sense of expansion and echo of the listening room with a small number of
reflected sounds, and localization of the sound image outside the head when listening with
headphones. High effects can be obtained. Also, when simulating the transfer functions from the
sound source to the left and right ears, instead of simulating the transfer functions to the left and
right ears, the transfer function indicating the difference between the two ears is simulated. The
difference between the sound quality and the sound quality can be minimized, and it contributes
to the reduction of the processing amount of the entire signal processing, and in particular,
because the same transfer function is used regardless of the arrival direction of sound as its
transfer function Very large. When the equalizer signal processing for sound quality correction is
applied to the output signal, the sound quality of the original sound can be more effectively
maintained. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a headphone
reproduction apparatus according to a first embodiment. FIG. 2 is an explanatory view of the
arrival of the direct sound from the right speaker to the left and right ears. FIG. 3 is an
explanatory view of the arrival of the direct sound and the reflected sound from the right speaker
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to the left and right ears. FIG. 4 is a frequency characteristic diagram of a transfer function
showing the difference between both ears. FIG. 5 is a block diagram of a headphone reproduction
apparatus according to a second embodiment. FIG. 6 is a block diagram of a conventional
headphone reproduction apparatus. [Explanation of the code] 1, 14: Input terminal of stereo
sound signal 2, 15: Multiplier 3, 16: Filter circuit 4, 17: Reflected sound generation circuit 5: Left
reflected sound signal group reaching the left ear 6: Left Left reflected sound signal group
reaching the ear 7: Right reflected sound signal group reaching the right ear 8: Right reflected
sound signal group reaching the right ear 9: 22: Delay multiplication circuit 10, 12, 23, 25:
Adder 11, 24: Low pass filter circuit 13, 26: Output terminal to headphone 18: Right reflected
sound signal group reaching right ear 19: Right reflected sound signal group reaching right ear
20: Left reflected sound reaching left ear Signal group 21: Left reflected sound signal group
reaching the left ear 27, 28: High pass filter circuit
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