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JPH1127799

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPH1127799
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
sound image control apparatus for generating a sound image at a virtual sound source position
other than the speaker arrangement position using two speakers.
[0002]
2. Description of the Related Art A sound image control apparatus has been developed which
generates a sound image at a virtual sound source position other than the speaker position using
two speakers, and home audio such as home theater as well as audio equipment for amusement
facilities. It is going to be applied to the device.
[0003]
Sound image control used in the sound image control apparatus is usually performed using a
digital filter such as an FIR (finite impulse response) filter or an IIR (infinite impulse response)
filter.
[0004]
FIG. 9 shows a conventional sound image control circuit using an FIR filter.
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1
The sound image control circuit includes an input terminal PI, a left channel output terminal UL,
and a right channel output terminal UR.
The first FIR filter 101 is connected between the input terminal P1 and the left channel output
terminal UL. The second FIR filter 102 is connected between the input terminal P1 and the right
channel output terminal UR.
[0005]
The input signal a input to the input terminal PI is sent to each of the FIR filters 101 and 102,
and filter processing is performed according to the filter coefficient of each of the FIR filters 101
and 102. The output signal b1 of the first FIR filter 101 is sent to the speaker for the left
channel, and the output signal b2 of the second FIR filter 102 is sent to the speaker for the right
channel.
[0006]
The method of obtaining the filter coefficients of the FIR filters 101 and 102 will be described
with reference to FIG.
[0007]
The definition of each symbol in FIG. 10 is as follows.
[0008]
A: Listener SPL, SPR: Speaker WL, WR: Transfer function from the virtual sound source O to the
left and right ears of the listener A HLL, HLR, HRL, HRR: Left and right speakers SPL, SPR to the
left and right of the listener A Transfer function to the ear
[0009]
Assuming that a signal to be output from the virtual sound source O is X (ω), the following
equation 1 must be established to output a signal equivalent to the signal X (ω) from the
speakers SPL and SPR.
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In Equation 1, Lout indicates the output signal from the speaker SPL, and Rout indicates the
output signal from the speaker SPR.
[0010]
Therefore, the frequency characteristics H 1 (ω) and H 2 (ω) of the FIR filters 101 and 102 for
localizing the input signal to the virtual sound source position can be obtained by the following
equation (2).
Then, the filter coefficients of the FIR filters 101 and 102 are obtained by performing inverse
Fourier transform on the obtained frequency characteristics H1 (ω) and H2 (ω) respectively.
[0011]
FIG. 11 shows the frequency characteristics H 1 (ω) and H 2 (ω) of the FIR filters 101 and 102
used when the virtual sound source O is localized in the lateral direction of the listener A as
shown in FIG. There is.
The broken line L1 in FIG. 11 indicates the frequency characteristic H1 (ω) of the FIR filter 101,
and the broken line L2 in FIG. 11 indicates the frequency characteristic H2 (ω) of the FIR filter
102.
[0012]
FIG. 12 shows a sound image control circuit equivalent to that of FIG. Assuming that the
frequency characteristic of the first FIR filter 101 of the sound image control circuit of FIG. 9 is H
1 (ω) and the frequency characteristic of the second FIR filter 102 is H 2 (ω), the first in the
sound image control circuit of FIG. The frequency characteristic of the FIR filter 201 is H 1 (ω),
and the frequency characteristic of the second FIR filter 202 is H 2 (ω) / H 1 (ω).
[0013]
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In the conventional sound image control circuit, since the coefficients of the FIR filter are
obtained using the transfer function, the optimum listening position of the listener is limited.
Therefore, when listening at a position shifted from the predetermined optimum listening
position, it is not possible to localize the virtual sound source at the desired position.
[0014]
Also, as apparent from the non-uniformity of the frequency characteristics in FIG. 11, since the
sound far from the sound quality to be originally output from the virtual sound source is output
from the speakers SPL and SPR, the timbre is not suitable for timbre. Nature and discomfort will
remain. This effect becomes more remarkable as the listening position deviates from the
optimum listening position.
[0015]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a sound image
control apparatus in which it is difficult to feel discomfort when the listening position deviates
from the optimum listening position.
[0016]
A first sound image control apparatus according to the present invention is a sound image
control apparatus for generating a sound image at a virtual sound source position other than the
speaker arrangement position using two speakers, an FIR filter and an input. The signal
processing apparatus further comprises: means for outputting the signal as it is as an audio
signal to the first speaker; and means for sending an input signal to the FIR filter and outputting
the output of the FIR filter as an audio signal to the second speaker. Do.
[0017]
The filter coefficients of the above FIR filter are obtained by filtering the input signal using two
FIR filters to generate two output signals. The filter characteristics of each FIR filter in the
conventional apparatus are H 1 (ω) and H 2 (ω). Then, they are obtained from their ratio H2 (ω)
/ H1 (ω).
[0018]
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A second sound image control apparatus according to the present invention is a sound image
control apparatus that generates a sound image at a virtual sound source position other than the
speaker arrangement position using two speakers, a frequency characteristic control unit that
performs frequency characteristic control, phase characteristic control Control of the input signal
by the frequency characteristic control unit and the phase characteristic control unit performed
by the frequency characteristic control unit and the phase characteristic control unit. It is
characterized in that it comprises means for outputting the signal as an audio signal to the
second speaker.
[0019]
The filter coefficients of the filter used in the frequency characteristic control unit are the filter
characteristics of each FIR filter in the conventional device that filters the input signal using two
FIR filters to generate two output signals H 1 (ω) , H 2 (ω), they are determined based on their
ratio H 2 (ω) / H 1 (ω).
The phase characteristic control unit performs one or both of delay processing and phase
inversion processing.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
[0021]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
[0022]
[1] Description of the First Embodiment
[0023]
FIG. 1 shows a sound image control circuit.
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The case where the virtual sound source position O is localized in the lateral direction of the
listener A as shown in FIG. 2 will be described.
[0024]
The sound image control circuit includes an input terminal PI, a left channel output terminal UL,
and a right channel output terminal UR.
The input terminal P1 and the left channel output terminal UL are directly connected.
The FIR filter 1 is connected between the input terminal P1 and the right channel output
terminal UR.
[0025]
The input signal a input to the input terminal PI is sent to the left channel speaker via the left
channel output terminal UL.
Further, the input signal a input to the input terminal PI is sent to the FIR filter 1, and filter
processing is performed according to the filter coefficient of the FIR filter 1.
The output signal b of the FIR filter 1 is sent to the right channel speaker via the right channel
output terminal UR.
[0026]
As the FIR filter 1, a 256-tap FIR filter is used.
The filter coefficients of the FIR filter 1 are obtained as follows. That is, in the conventional
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apparatus of FIG. 9, the frequency characteristics of each of the FIR filters 101 and 102 used
when the virtual sound source position O is localized in the lateral direction of the listener A as
shown in FIG. Let ω). Then, H 3 (ω) = H 2 (ω) / H 1 (ω) is calculated and the inverse Fourier
transform is performed to obtain the filter coefficient of the FIR filter 1.
[0027]
A broken line L3 in FIG. 3 indicates a frequency characteristic H3 (ω) when the frequency
characteristics H1 (ω) and H2 (ω) are as shown in FIG.
[0028]
The first embodiment corresponds to a circuit obtained by removing the first FIR filter 201 from
the equivalent circuit shown in FIG.
As shown in FIG. 1, even if the first FIR filter 201 is removed from the equivalent circuit shown in
FIG. 12, between the output signal appearing at the left channel output terminal UL and the
output signal appearing at the right channel output terminal UR Since the relative relationship
between the frequency and the phase is equal to the relative relationship between the equivalent
circuit of FIG. 12 or the conventional device of FIG. 9, when the listener is located at the optimal
listening position, Can be localized. When the listening position deviates from the optimum
listening position, the sound image can not be localized at a predetermined virtual sound source
position, but since the original sound is output from one of the speakers, the user does not feel
uncomfortable.
[0029]
[2] Description of the Second Embodiment
[0030]
FIG. 4 shows a sound image control circuit when the virtual sound sources OL and OR for two
channel signals are localized on the left and right sides of the listener A as shown in FIG.
[0031]
The sound image control circuit is provided with a left channel input terminal PI1 to which the
left channel audio signal a1 is input, a right channel input terminal PI2 to which the right
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channel audio signal a2 is input, a left channel output terminal UL, and a right channel. And an
output terminal UR.
[0032]
The audio signal a1 input to the left channel input terminal PI1 is sent to the first adder 11 and
also sent to the first FIR filter 21.
The audio signal a2 input to the right channel input terminal PI2 is sent to the second adder 12
and also sent to the second FIR filter 22.
The filter coefficients of the first FIR filter 21 and the second FIR filter 22 are the same as the
filter coefficients of the FIR filter 1 in the first embodiment.
[0033]
In the first adder 11, the audio signal a1 and the output of the second FIR filter 22 are added.
The output of the first adder 11 is sent to the left channel speaker via the left channel output
terminal UL. In the second adder 12, the audio signal a 2 and the output of the first FIR filter 21
are added. The output of the second adder 12 is sent to the right channel speaker via the right
channel output terminal UR.
[0034]
[3] Description of Modification of First Embodiment
[0035]
FIG. 6 shows a modification of the first embodiment.
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In this sound image control circuit, a circuit comprising a frequency characteristic control unit
31 and a phase characteristic control unit 32 is used in place of the FIR filter 1 of the sound
image control circuit of FIG.
[0036]
The frequency characteristic control unit 31 uses an analog filter or an IIR filter. As the filter
characteristic of the filter used in the frequency characteristic control unit 31, one having one or
both of a band rejection filter characteristic and a low pass filter characteristic is used. In this
case, the band rejection filter characteristic has an acuteness Q of 1.0 or more and a center
rejection frequency of 2.0 to 3.0 [kHz]. On the other hand, the low-pass filter characteristic has a
cutoff frequency of 1.0 to 5.0 [kHz]. These characteristics are obtained from the frequency
characteristics H3 = H2 / H1 of the FIR filter 1 in the first embodiment.
[0037]
In this example, the frequency characteristic control unit 31 performs filter processing using a
four-dimensional IIR filter. As a four-dimensional IIR filter constituting the frequency
characteristic control unit 31, a two-dimensional IIR filter (band-stop filter) having a sharpness Q
of 16.0, a center rejection frequency of 2.5 [kHz] and a gain of 0 [dB] And a two-dimensional IIR
filter (low pass filter) with a sharpness Q of 1 / (21/2), a low pass filter cutoff frequency of 3.0
[kHz], and a gain of 0 [dB] Be The above-mentioned characteristic parameters of the fourdimensional IIR filter can be obtained from the frequency characteristic H3 = H2 / H1 of the FIR
filter 1 in the first embodiment.
[0038]
A broken line L4 in FIG. 7 indicates the frequency characteristic of this synthesis filter. The
broken line L3 in FIG. 7 shows the frequency characteristic H3 of the FIR filter 1 in the first
embodiment. That is, the frequency characteristic of the four-dimensional IIR filter used in the
frequency characteristic control unit 31 is determined so as to approximate to the frequency
characteristic H3 of the FIR filter 1 in the first embodiment.
[0039]
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The phase characteristic control unit 32 performs one or both of delay processing and phase
inversion processing on the input signal. In this example, the phase characteristic control unit 32
performs 0.3 [msec] delay processing and phase inversion processing.
[0040]
In this modification, in addition to the advantages of the first embodiment, there is an advantage
that the processing amount is reduced as compared with the prior art. That is, assuming that the
number of taps of each of the FIR filters 101 and 102 is N in the conventional apparatus of FIG.
9, 2N multiplications and 2N-1 additions are required. On the other hand, in the above
modification, nine multiplications and eight additions are required. Since the number N of taps of
the FIR filter is usually several hundreds, the amount of processing is reduced significantly in this
modification as compared with the conventional device.
[0041]
[4] Description of Modification of Second Embodiment
[0042]
FIG. 8 shows a modification of the second embodiment.
In this sound image control circuit, a circuit comprising a frequency characteristic control unit
31 and a phase characteristic control unit 32 is used in place of the FIR filters 21 and 22 of the
sound image control circuit of FIG. The frequency characteristic control unit 31 of FIG. 8 is the
same as the frequency characteristic control unit 31 of FIG. Further, the phase characteristic
control unit 32 of FIG. 8 is the same as the phase characteristic control unit 32 of FIG.
[0043]
According to the present invention, when the listening position deviates from the optimum
listening position, it becomes difficult to feel discomfort.
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[0044]
Brief description of the drawings
[0045]
1 is a block diagram showing a sound image control circuit according to a first embodiment of
the present invention.
[0046]
2 is a schematic view showing the localization position of the virtual sound source.
[0047]
3 is a graph showing the frequency characteristics of the FIR filter of FIG.
[0048]
4 is a block diagram showing a sound image control circuit according to a second embodiment of
the present invention.
[0049]
5 is a schematic view showing the localization position of the virtual sound source.
[0050]
6 is a block diagram showing a modification of the first embodiment.
[0051]
7 is a graph showing the frequency characteristics of the four-dimensional IIR filter used in the
frequency characteristic control unit of FIG.
[0052]
<Figure 8> It is the block diagram which shows the deformation example of form of 2nd
execution.
[0053]
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9 is a block diagram showing a conventional sound image control circuit.
[0054]
10 is a schematic diagram for explaining the method of determining the coefficient of each FIR
filter of FIG.
[0055]
11 is a graph showing the frequency characteristics of each FIR filter of FIG.
[0056]
12 is a block diagram showing an equivalent circuit of FIG.
[0057]
Explanation of sign
[0058]
1 FIR Filter 11, 12 Adder 21, 22 FIR Filter 31 Frequency Characteristic Control Unit 32 Phase
Characteristic Control Unit
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