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JP2005039509

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DESCRIPTION JP2005039509
PROBLEM TO BE SOLVED: To obtain a stereo characteristic without deterioration of wind noise
in a wind noise band, obtain a flat gain characteristic over the entire stereo operation processing
band, and simplify an equalizer at a subsequent stage. SOLUTION: A stereo microphone device
according to the present invention comprises band dividing means 55 to 58 for dividing an audio
band from at least one of a plurality of nondirectional microphones 51 and 52 into a plurality of
bands, band dividing means 56, The first band output via the first delay means 60, 61 for time
delaying the first band signal from 57 is added to the outputs of the other microphones, and the
second from the band division means 55, 58 is added. The second band output via the second
delay means 59 and 62 for delaying the band signal in the second band is subtracted from the
outputs of the other microphones, and the adders 63 to 66 are provided. [Selected figure] Figure
5
Stereo microphone device and stereo calculation method
[0001]
The present invention relates to, for example, a stereo microphone device and a stereo
calculation method for recording stereo sound.
[0002]
As a technique for generating a stereo sound field with a built-in microphone (hereinafter
referred to as a microphone) of a video camera, a built-in stereo microphone described in Patent
Document 1 is generally used.
10-05-2019
1
[0003]
FIG. 8 shows a conventional stereo arithmetic circuit according to Patent Document 1.
First, Rch and Lch audio signals are input from the microphones 101 and 102, respectively, and
the signal levels are optimized by the amplifiers (AMPs) 103 and 104. The Rch signal and the +
terminal of the adder 109 are generally LPF (Low Pass Filter) Are input to the delay unit DL
(Deray Line) 105.
Similarly, the Lch signal is input to the positive terminal of the adder 110 and the delay unit
DL106, and the low-pass components of the voice band delayed by the DLs 105 and 106 have
appropriate levels by the attenuators ATT (Attenator) 107 and 108, respectively. And are input to
the-terminals of the adders 110 and 109.
[0004]
In the adders 109 and 110, matrix processing is performed by subtracting low frequency
component signals from the other channels, that is, signals below the cutoff frequency of the LPF
set by the DLs 105 and 106, and stereo in the low frequency band The sound field is reproduced.
Further, the outputs of the adders 109 and 110 are adjusted in frequency characteristics by
equalizers (equalizers) 111 and 112 formed of filter circuits, and are output from the terminals
113 and 114 as Rch and Lch signals.
[0005]
Here, FIG. 9 shows stereo directivity characteristics generated by the stereo operation circuit of
FIG. First, in the stereo operation circuit of FIG. 8, nondirectional microphones having directivity
in all directions are used as microphones 101 and 102, and delay units DL 105 and 106 have
time delays depending on the distance between the microphones, and normal audio The Lch and
Rch signals are input with a phase difference corresponding to this time delay, and the signals
are subtracted from each other to be subjected to stereo operation processing, as shown in FIG.
9A before stereo operation processing. The directional characteristics of Lch (solid line) and Rch
(dotted line) almost coincide with each other as shown by 121 and show monaural
characteristics, but after stereo operation processing, Lch (solid line) and Rch as shown in FIG.
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The directional characteristics (dotted line) are separated in the left and right direction as
indicated by 122 and 123, respectively, and show stereo characteristics.
[0006]
However, since the wind noise signal is input to Lch and Rch signals with random phase
difference, this stereo calculation processing is performed, and the level is degraded by 6 dB
when the input signals are added in phase by adders 109 and 110, for example Furthermore, in
order to increase the gain of the wind noise band by the EQs 111 and 112 in the subsequent
stage, there is a problem that the wind noise is greatly emphasized as compared to the voice
signal. In particular, with the miniaturization of products in recent years, the distance between
the microphones has been narrowed, and this tendency is becoming more pronounced because
the amount of gain up in the subsequent EQ is further increased.
[0007]
Next, FIG. 10 shows an example of the frequency characteristic of a wind noise signal in a
general video camera. The frequency characteristic 131 of wind noise increases in level at 1 / F
characteristic (F is frequency) as the frequency decreases from about 1 kHz. However, in
practice, the extremely low frequency often has a peak near about 200 Hz because the level
decreases due to the characteristics of the microphone unit used and the coupling capacitor of
the analog circuit.
[0008]
Patent No. 2946638 gazette
[0009]
However, since the stereo operation circuit of the prior application emphasizes the phase
difference of the L and R signals and the uncorrelated component which is the level difference,
wind noise which is mostly uncorrelated is emphasized when passing through this operation
circuit There is.
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3
In particular, due to the recent miniaturization of the equipment, the L and R microphone
spacings are narrowed, and a circuit-like correction by the stereo operation circuit is emphasized
because the structural stereo effect can not be obtained, and this problem becomes more
pronounced. Had the disadvantage of
[0010]
The present invention is made in view of this point, and by changing the method of stereo
operation processing in the wind noise band on the low band side and the other band on the high
band side respectively, the present invention is particularly effective in the wind noise band. The
present invention proposes a stereo microphone device and a stereo calculation method that can
obtain a stereo characteristic without deterioration of wind noise and obtain a flat gain
characteristic over the entire stereo calculation processing band and can simplify the equalizer at
the subsequent stage.
[0011]
In order to solve the above problems and achieve the object of the present invention, a stereo
microphone device according to the present invention divides a voice band from at least one
nondirectional microphone of a plurality of nondirectional microphones into a plurality of bands.
Means, and the first band output via the first delay means for delaying the first band signal from
the band dividing means in at least one non-directional microphone other than the nondirectional microphone divided by the band dividing means The second band output via the
adding means for adding with the output of the directional microphone and the second delay
means for delaying the second band signal from the band dividing means in time is divided by
the band dividing means It comprises subtraction means for subtracting from the output of at
least one nondirectional microphone other than the directional microphone.
[0012]
As a result, it is possible to provide a stereo microphone device that can suppress wind noise in
the low band and obtain flat stereo characteristics in the entire band.
[0013]
The stereo operation method according to the present invention further comprises the steps of:
dividing a voice band from at least one non-directional microphone of the plurality of nondirectional microphones into a plurality of bands by the band dividing means; The first band
output via the first delay means for time delaying the band signal of is added by the addition
means with the output of at least one nondirectional microphone other than the nondirectional
microphone divided by the band division means And at least one non-directional microphone
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4
other than the omnidirectional microphone divided by the band division means, and the second
band output through the second delay means for delaying the second band signal from the band
division means in time. And subtracting the output of the directional microphone from the output
of the directional microphone.
[0014]
As a result, it is possible to suppress the wind noise in the low band and perform stereo
calculation that can obtain flat stereo characteristics over the entire band.
[0015]
According to the first aspect of the present invention, by dividing the voice band into a plurality
of bands and making each band into stereo by separate stereo processing, frequency
characteristics can be made flat over the entire voice band, Since gain correction is not required,
it is possible to eliminate the need for an equalizer circuit configured with a filter or the like in
the subsequent stage.
[0016]
Further, according to the invention of claim 2, it is possible to obtain the stereo effect while
suppressing wind noise particularly in the low band susceptible to wind noise, and in the high
band, there is a frequency characteristic without level dip (null point). Thus, a flat stereo effect is
obtained over the entire audio band.
[0017]
Further, according to the invention of claim 3, the voice band is divided into a plurality of bands,
and the respective bands are made into stereo by separate stereo processing to make the
frequency characteristic flat over the entire voice band. Since no gain correction is required, it is
possible to eliminate the need for equalizer processing consisting of filter processing at a later
stage.
[0018]
Further, according to the invention of claim 4, it is possible to obtain the stereo effect while
suppressing wind noise particularly in the low band susceptible to wind noise, and in the high
band, there is no frequency dip (null point) in the frequency characteristic Thus, a flat stereo
effect is obtained over the entire audio band.
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[0019]
Therefore, in the present invention, it is an object of the present invention to perform stereo
operation processing without emphasizing wind noise in these wind noise bands which are
emphasized in the conventional stereo operation circuit.
Here, a stereo operation principle diagram of the stereo microphone device according to the
embodiment applied to the present invention will be described with reference to FIG.
[0020]
First, Rch and Lch audio signals are input from the microphones 1 and 2, respectively, and the
signal levels are optimized by the AMPs 3 and 4, and the Rch signal is input to one positive
terminal of the adder 7 and the delay device DL5.
Similarly, the Lch signal is input to one + terminal of the adder 8 and the delay unit DL6, and the
audio signal delayed by DL5 and 6 is input to the other + terminal of the adders 8 and 7.
In the adders 7 and 8, matrix processing is performed by subtracting signals delayed by DL 5 and
6 from each other's channels, and a stereo sound field is reproduced.
Further, the outputs of the adders 7 and 8 are output from the terminals 9 and 10 as Rch and
Lch signals.
[0021]
Further, the difference between the conventional stereo operation block diagram shown in FIG. 8
and the stereo operation process shown in FIG. 1 will be described.
First, an example of the frequency characteristic when T [sec] is delayed by the delay units DL
105 and 106 in the conventional process of FIG. 8 and subtracted from each other by the adders
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109 and 110 will be described with reference to FIG.
The horizontal axis is a frequency F [Hz] whose period is T, and the vertical axis is GAIN [dB].
Here, the solid line 21 is a frequency characteristic when there is no phase difference between
the input of the microphone 101 and the microphone 102, for example, when a sound is input
from the front center direction, and this is expressed by Equation 1.
(However, the input signal is a sine wave of amplitude 1, ATTs 107 and 108 are through.
)
[0022]
(Equation 1) sin ωt−sin ω (t−T) = 2 sin (πfT) · cos (ωt−πfT)
[0023]
According to Equation 1, the amplitude term 2 sin (πfT) has a minimum value (zero) for GAIN at
f = 0 [Hz] and f = 1 / T [Hz], and GAIN at f = 1/2 T [Hz] Is the maximum value (+6 dB), and the
outputs of the adders 109 and 110 are the same.
[0024]
On the other hand, when there is a phase difference between the input of the microphone 101
and the microphone 102 when the broken line 22 and the alternate long and short dash line 23
respectively have a phase difference, for example, the sound is input from any direction The
frequency characteristic of H is expressed by equation (2).
(However, the input signal is a sine wave of amplitude 1, ATTs 107 and 108 are through.
)
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[0025]
(Expression 2) sin ωt−sin ω (t− (T ± Ts)) = 2 sin (πf (T ± Ts)) · cos (ωt−πf (T ± Ts))
[0026]
In this case, the signal delay Ts (where T> Ts) due to the difference in distance from the sound
source is added to T to become a relative delay (T ± Ts).
Further, the sign ± changes depending on which of Lch and Rch is used as a reference
depending on the left and right direction of the sound source. Therefore, according to Equation 2,
the amplitude term 2 sin (πf (T ± Ts)) becomes the minimum value (zero) for GAIN at f = 0 [Hz]
and f = 1 / (T ± Ts) [Hz]. GAIN reaches the maximum value (+6 dB) at f = 1/2 (T ± Ts) [Hz], and
the outputs of the adders 109 and 110 correspond to the phase difference of the inputs as
shown by the broken line 22 and the alternate long and short dash line 23 A difference arises
and this becomes stereo separation.
[0027]
In general, the frequency characteristic is obtained by attenuating the low frequency range,
because f = 1 / 2T [Hz] or less is the stereo operation processing frequency band, and this is used
to level correct the low frequency range with the EQs 111 and 112 in the subsequent stage. The
characteristics are flattened.
[0028]
Next, FIG. 3 shows an example of the frequency characteristic when T [sec] is delayed by the
delay units DL5 and DL6 in the stereo operation principle diagram of the present invention in
FIG. 1 and added to each other by the adders 7 and 8. explain.
The horizontal axis is a frequency F [Hz] whose period is T, and the vertical axis is GAIN [dB].
Further, a solid line 31 is a frequency characteristic when there is no phase difference between
the inputs of the microphone 1 and the microphone 2, for example, when a sound is input from
the front center direction, this is expressed by Equation 3. (However, the input signal is a sine
wave of amplitude 1). )
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[0029]
(Equation 3) sin ωt + sin ω (t−T) = 2 cos (πfT) · sin (ωt−πfT)
[0030]
According to the equation 3, the amplitude term 2 cos (πfT) has the maximum value (+6 dB) of
GAIN at f = 0 [Hz] and f = 1 / T [Hz], and GAIN at f = 1/2 T [Hz] Becomes the minimum value
(zero), and the outputs of the adders 7 and 8 become the same.
[0031]
On the other hand, when there is a phase difference between the input of the microphone 1 and
the microphone 2 when the broken line 32 and the alternate long and short dash line 33
respectively have a phase difference, for example, the sound is input from an arbitrary direction
not equidistant from the microphone 1 and the microphone 2 The frequency characteristic of is
expressed by equation (4).
(However, the input signal is a sine wave of amplitude 1).
)
[0032]
(Equation 4) sin ωt + sin ω (t− (T ± Ts)) = 2 cos (πf (T ± Ts)) · sin (ωt−πf (T ± Ts))
[0033]
In this case, the signal delay Ts (where T> Ts) due to the difference in distance from the sound
source is added to T to become a relative delay (T ± Ts).
Further, the sign ± changes depending on which of Lch and Rch is used as a reference
depending on the left and right direction of the sound source. Therefore, according to Equation 4,
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the amplitude term 2 cos (πf (T ± Ts)) becomes maximum value (+6 dB) of GAIN at f = 0 [Hz]
and f = 1 / (T ± Ts) [Hz]. GAIN becomes the minimum value (zero) at f = 1/2 (T ± Ts) [Hz], and
the outputs of adders 7 and 8 correspond to the phase difference of the inputs as shown by
broken line 32 and dashed dotted line 33. A difference arises and this becomes stereo separation.
[0034]
Then, if f = 1 / 2T [Hz] or less is set as the stereo operation processing band, it has frequency
characteristics in which the high region is attenuated.
[0035]
Here, if the delay T is set to 50 [μS] in one example in FIGS. 2 and 3, the frequency is 1/2 T at
10 [kHz], and the wind noise band mentioned above is sufficiently low for the stereo operation
processing band. In the frequency characteristic in the case of subtraction applied to the
conventional example of FIG. 2, it is necessary to raise the gain to near 0 dB by the EQ at the
subsequent stage, but the wind noise is deteriorated. It is not necessary to raise the low band
further with the EQ in the latter stage in the frequency characteristic in the case of addition
applied to the case, and conversely, if necessary, the gain will be lowered to around 0 dB. There
is an advantage to be improved without.
[0036]
Therefore, in the stereo operation process of the stereo microphone device according to the
embodiment applied to the present invention, the wind noise can be suppressed and the stereo
operation process can be performed, but the problem in FIG. 3 is that the null frequency at which
GAIN is −− It is in the stereo operation processing band, and the signal delay Ts changes
depending on the sound source direction.
That is, if the delay T is set to 50 [μS] as described above, the frequency is 1/2 T at 10 [kHz], a
null point occurs in the stereo operation processing band, and the point of the frequency 1/2 T is
Ts. , 1/2 (T + Ts) and 1/2 (T-Ts).
Further, if the delay T is further reduced, the null point is shifted to the high frequency, and this
problem can be avoided. However, the stereo separation can not be made large and the result of
the stereo operation processing can not be achieved.
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[0037]
Therefore, in the stereo operation processing of the stereo microphone device of the embodiment
applied to the present invention, the stereo operation processing band is divided, and in the wind
noise band, the wind noise is the frequency characteristic in the case of addition applied to the
present invention of FIG. In the other bands, the above problem is solved by using the frequency
characteristics in the case of subtraction applied to the conventional example of FIG.
[0038]
First, a stereo operation block example 1 of the stereo microphone device according to the
embodiment applied to the present invention will be described with reference to FIG.
Rch and Lch audio signals are input from the microphones 51 and 52, respectively, and the
signal levels are optimized by the AMPs 53 and 54. The Rch signal is the + terminal of the adder
65, the band dividing means (2) 55 and the band dividing means (1) It is input to 56. Similarly,
the Lch signal from the AMP 54 is input to the positive terminal of the adder 66, and the band
dividing means (1) 57 and the band dividing means (2) 58. Here, the band division means (1) 56
and the band division means (1) 57 extract the same band 1 signal, but this band 1 is set to the
wind noise band shown in FIG. Similarly, the same band 2 signal is extracted by the band dividing
means (2) 55 and the band dividing means (2) 58, and this is set to a second band other than
band 1.
[0039]
The Rch band 2 signal divided from the band division means (2) 55 is delayed via the delay unit
DL (2) 59, and the Rch band 1 signal divided from the band division means (1) 56 is delayed 1)
Delayed through 60. Also, the Lch band 1 signal divided from the band division means (1) 57 is
delayed via the delay unit DL (1) 61, and the Lch band 2 signal divided from the band division
means (2) 58 is delayed by the delay unit DL (2) delayed through 62;
[0040]
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The delayed Rch band 1 signal is input to the addition input terminal of the adder 63, the Rch
band 2 signal is input to the subtraction input terminal of the adder 63, the Rch band 1 signal is
added by the adder 63, and the Rch band is added. 2 signals are subtracted. The Lch signal and
the Rch band 1 signal are added by the adder 66, the Rch band 2 signal is subtracted, and the
resulting signal is output from the terminal 68 as the Lch signal.
[0041]
The Lch band 1 signal delayed similarly is input to the addition input terminal of the adder 64,
the Lch band 2 signal is input to the subtraction input terminal of the adder 64, and the Lch band
1 signal is added by the adder 64, The Lch band 2 signal is subtracted. The Rch signal and the
Lch band 1 signal are added by the adder 65, the Lch band 2 signal is subtracted, and the
resulting signal is output from the terminal 67 as the Rch signal.
[0042]
Here, the band dividing means in FIG. 5 will be further described with reference to FIG. FIG. 4A
shows an example of band division by BPF (Band Pass Filter). A band (1) 41 is extracted by BPF 1
and a band (2) 42 is extracted by BPF 2. Here, the band 1 which is the wind noise band and the
other band 2 in the stereo operation block example 1 of FIG. 5 correspond to the band (1) 41 and
the band (2) 42. 4B is an example of band division by LPF (Low Pass Filter). Band (1) 44 is
extracted by LPF (1) 43, and the output of LPF (1) 43 is subtracted from the output of LPF (2)
45. By doing this, the band (2) 46 is extracted. Then, as described above, the band (1) 44 is set to
the band 1 which is the wind noise band in the stereo operation block example 1 of FIG. 5, and
the band (2) 46 is set to the other band 2.
[0043]
Next, an example of the frequency characteristic in stereo operation processing of the stereo
microphone device of the embodiment applied to the present invention of FIG. 5 will be
described with reference to FIG. First, in FIG. 5, a delay of T1 [sec] is applied by the delay units
DL (1) 60 and DL (1) 61, and the output frequency when calculated by the adder 63, the adder
64, the adder 65, and the adder 66. An example of characteristics is shown, and a band (1) 77 of
a band determined with a frequency of 1/2 T1 [Hz] or less with T1 as a period, and T2 [sec] by
delay devices DL (2) 59 and DL (2) 62 Of the output frequency when calculated by the adder 63,
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the adder 64, the adder 65, and the adder 66. The frequency 1/2 T2 [Hz] and the 1/2 The band
is divided into band (2) 78 of the band determined by
[0044]
Furthermore, solid lines 71 and 74 indicate that there is no phase difference between the inputs
of the microphones 51 and 52, while broken lines 72 and 75 and alternate long and short dash
lines 73 and 76 indicate that there is a phase difference between the inputs of the microphones
51 and 52, respectively. Therefore, if the respective delays T1 and T2 are determined so that the
frequency characteristics become flat when the band (1) 77 and the band (2) 78 are added as
shown in FIG. 6, it is necessary to increase the gain in the wind noise band Since no stereo noise
is obtained, wind noise can be suppressed, and conventional stereo characteristics can be
obtained outside the wind noise band. Furthermore, since the frequency characteristics are flat,
the EQ in the subsequent stage can be simplified.
[0045]
Further, FIG. 7 shows a stereo operation block example 2 of the stereo microphone device of the
embodiment applied to the present invention, and will be described. Microphones 81, 82 and 83
are non-directional microphones arranged, for example, in an equilateral triangle, receive Rch,
Lch and Cch audio signals respectively, optimize the signal levels with AMPs 84, 86 and 85, and
add Rch signals Similarly, the Lch signal is input to the addition input terminal of the adder 93,
the Cch signal is input to the band dividing means (2) 87 and the band dividing means (1) 88,
and the band is divided In the dividing means (1) 88, the band 1 is extracted as in FIG. 5 and set
to the wind noise band shown in FIG. The band dividing means (2) 87 extracts the band 2 and
this is set to the band 2 excluding the band 1.
[0046]
Then, the Cch band 2 signal divided from the band division means (2) 87 is delayed via the delay
unit DL (2) 89, and the Cch band 1 signal divided from the band division means (1) 88 is delayed
1) Delayed through 90.
[0047]
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The delayed Cch band 1 signal is input to the addition input terminal of the adder 91, the Cch
band 2 signal is input to the subtraction input terminal of the adder 91, the Cch band 1 signal is
added by the adder 91, and the Cch band is added. 2 signals are subtracted.
The Rch signal and the Cch band 1 signal are added by the adder 92, the Cch band 2 signal is
subtracted, and the resulting signal is output from the terminal 94 as the Rch signal. The Lch
signal and the Cch band 1 signal are added by the adder 93, the Cch band 2 signal is subtracted,
and the resulting signal is output from the terminal 95 as an Lch signal.
[0048]
As in the stereo operation block example 2 of the stereo microphone device of the embodiment
applied to the present invention of FIG. 7, even in the case of two or more microphones, the
stereo effect can be obtained while obtaining the same effect as FIG. . In the present invention,
ATT and EQ are not necessarily required.
[0049]
The present invention can be applied to the case of generating a stereo sound field with the builtin microphone of a video camera.
[0050]
It is a stereo calculation principle figure of the stereo microphone apparatus of embodiment
applied to this invention.
It is a figure which shows the example of a frequency characteristic in subtraction. It is a figure
which shows the example of a frequency characteristic in addition. FIG. 4 (a) shows band division
by BPF, and FIG. 4 (b) shows band division by LPF. It is a figure showing example stereo
operation block 1 of a stereo microphone device of an embodiment applied to the present
invention. It is a figure showing an example of a frequency characteristic in stereo operation
processing of a stereo microphone device of an embodiment applied to the present invention. It
is a figure which shows stereo calculation block example 2 of the stereo microphone apparatus
of embodiment applied to this invention. It is a figure which shows the conventional stereo
operation block. FIG. 9A is a view before stereo operation processing, and FIG. 9B is a view after
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stereo operation processing in a video camera. It is a figure which shows the frequency
characteristic example of the wind noise signal in a video camera.
Explanation of sign
[0051]
1, 2 ... microphone, 3, 4 ... AMP, 5, 6 ... DL, 7, 8 ... adder, 9, 10 ... terminals, 21 to 23 ... subtraction
frequency characteristics, 31 to 33 ... addition frequency characteristics, 41 ... band 1, 42 ... Band
2, 43 ... LPF 1, 44 ... Band 1, 45 ... LPF 2, 46 ... Band 2, 51, 52 ... Microphone, 53, 54 ... AMP, 56,
57 ... Band dividing means (1), 55, 58: Band division means (2), 60, 61: Delay device DL (1), 59,
62: Delay device DL (2), 63 to 66: Adder, 67, 68: Terminal, 71 to 73: Subtraction frequency
Characteristics 74 to 76 Addition frequency characteristics 77 Band 1 78 Band 2 81 82 83
Microphone, 85 85 86 AMP, 88 Band splitting means (1) 87 Band splitting means (2), 90 ... delay
device DL (1), 89 ... delay device DL ( ), 91 to 93 ... adder, 94, 95 ... terminal
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