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JP2005142608

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DESCRIPTION JP2005142608
PROBLEM TO BE SOLVED: To obtain small and good stereo sound. SOLUTION: The first to fourth
microphones are arranged such that a straight line connecting the first and second microphones
is perpendicular to a straight line connecting the third and fourth microphones. A first
synthesizer that delays the output of the second microphone to combine with the output of the
first microphone, and a second synthesizer that delays the output of the fourth microphone to
combine with the output of the third microphone And the signal from the attenuator that
attenuates the output of the second synthesizer and the output of the first synthesizer to form
the first channel voice, and the output of the first synthesizer from the output of the attenuator
The signal from which the output has been subtracted is taken as the sound of the second
channel. [Selected figure] Figure 2
Signal processor
[0001]
The invention relates to an apparatus for processing audio signals.
[0002]
Conventionally, so-called pair microphone systems in which two unidirectional microphones are
used to construct a stereo microphone and arranged at an angle called a directional axis angle
cause differences in the sound collection characteristics on the left and right, enabling stereo
recording It was
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However, in this method, the relationship between the movement of the sound source and the
recorded sound image is studied, and it is better that a so-called MS microphone composed of a
mid microphone and a side microphone is superior to this pair microphone method in terms of
sound image localization. I understand.
[0003]
This MS microphone, as shown in FIG. 10, arranges the microphones of a uni-directional mid
microphone shown at 401 and a bi-directional side microphone shown at 402 in the lateral
direction toward the front of the sound collecting direction. The left and right voices are obtained
by signal processing of each microphone. This is an advantage that the sensitivity in the forward
direction is high, and the sensitivity in the back direction is advantageously lowered for the
sound of the subject reflected in the lens, and the video camera is advantageous for the noise
emitted from the main body etc. was there. The polar pattern of the left channel in this case is
shown in FIG. 5, and the polar pattern of the right channel is shown in FIG. UnexaminedJapanese-Patent No. 11-205888 gazette
[0004]
However, in the prior art MS microphone, while the sound field of the recorded sound is good,
the above-mentioned mid microphone is a unidirectional microphone element and the side
microphone is a bidirectional microphone element. It is weak to vibration and wind noise, and it
is easy to pick up mechanical vibration noise etc. when it is used for a video camera, and not only
wind noise etc. becomes a problem, but both microphone elements are expensive and
disadvantageous in cost. Furthermore, in order to maintain the respective acoustic
characteristics, it is necessary to take a lot of space around the microphone element, which is not
suitable for miniaturization.
[0005]
Further, in the shooting condition of the video camera, the positional relationship between the
photographer and the microphone is roughly shown in FIG. The direction of the photographer's
mouth is located approximately 150 degrees from the front, and as can be seen from FIGS. 5 and
6, since the sensitivity of that direction is low for both channels, the photographer is not So-
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called narration voices are difficult to enter, and depending on the image, there may be a lack of
realism.
[0006]
In order to solve this problem, another microphone was placed near the photographer's mouth,
and it was possible to record only narration well. However, the volume of the additional
microphone and the increase of the microphone amplifier, etc. Not only is this not only
disadvantageous in terms of cost but also many video cameras do not have terminals for
inputting additional microphones.
[0007]
An object of the present invention is to solve such a problem and to provide a signal processing
device capable of obtaining a compact and good stereo sound.
[0008]
The output signal of the second microphone element is delayed by the delay means, and the
output signal of the first microphone element output is equivalent to the output of the
unidirectional microphone by subtraction using the first combining means.
When the output signal of the second combining means is subtracted from the output signal of
the third microphone element by the second combining means, the output signal becomes
equivalent to the output of the bidirectional microphone.
The attenuator attenuates the output signal of the second synthesizer, and the third synthesizer
synthesizes the output signal of the first synthesizer and the output signal of the attenuator to
produce the left channel sound. The inverter inverts the output signal of the attenuator, and the
fourth synthesizer synthesizes the output signal of the first synthesizer and the output signal of
the inverter to generate the right channel sound.
[0009]
The attenuation amount of the attenuator determines the directional axis angle of the stereo
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microphone. The second delay means delays the signal of the fourth microphone, and the fifth
synthesizer synthesizes the signal of the second microphone and the signal of the second delay
means, and is unidirectional with the left rear facing front Generate a microphone and configure
a narration microphone. The sixth combiner combines the signal of the fifth combiner and the
signal of the first combiner to combine the left channel signal and the narration, and the seventh
combiner combines the signal of the fifth combiner and the fifth combiner. The signals of the two
synthesizers are combined, the signal of the right channel and the narration are combined, and
the narration is mixed to the left and right channels and mixed as monaural sound.
[0010]
The switch means performs on / off control of the narration voice.
[0011]
As described above, according to the present invention, the MS microphone which is superior in
sound image localization to the paired microphone method can be configured at low cost, and the
photographer desires without an increase in additional microphone volume or microphone
amplifier. The photographer's narration voice can be easily collected at the time of shooting, and
the size and cost are very effective.
Also, even if the form of the video camera changes or the direction of the photographer's hold is
to the right with respect to the video camera, the uni-directional microphone facing the
photographer's mouth of the four microphone elements It can be configured and can also
produce effects under different conditions.
[0012]
Also, in the case where a plurality of photographers share a common use, it is also possible to
switch the direction of the narration microphone in accordance with the hold direction when the
hold direction of the video camera is different for each individual. If the photographer or narrator
is not in the opposite direction of the subject, i.e., directly behind the video camera, the
microphones on the front and back sides can be used to collect the sound from the back side.
[0013]
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Hereinafter, examples of the present invention will be described.
[0014]
1 and 2 show Embodiment 1 of the present invention.
In FIG. 1, 1, 2, 3 and 4 indicate nondirectional microphone elements, the microphone element 1
is a sound source direction toward the sound source direction, the microphone element 2 is a
recording side toward the sound source direction, and the microphone element 3 is a sound
source The microphone element 4 is disposed on the left side in the direction and on the right
side in the sound source direction. The straight line connecting the microphone elements 1 and 2
and the straight line connecting the microphone elements 3 and 4 are in a vertical relationship.
Let L be the distance between the microphone elements 1 and 2 and the distance between the
microphone elements 3 and 4.
[0015]
2, 11 is an input terminal for inputting an output signal of the microphone element 1 of FIG. 1,
12 is an input terminal for inputting an output signal of the microphone element 2 of FIG. 1, and
13 is a microphone element 3 of FIG. And an input terminal 14 for inputting an output signal of
the microphone element 4 of FIG.
[0016]
15 is a first amplifier for amplifying the signal from the input terminal 11, 16 is a second
amplifier for amplifying the signal from the input terminal 12, 17 is a third amplifier for
amplifying the signal from the input terminal 13, and 18 is A fourth amplifier for amplifying the
signal from the input terminal 14, 19 is a first delay means for delaying the output signal of the
second amplifier 16, and 21 is a first inversion for inverting the phase of the output signal of the
delay means 19. A first combiner 23 combines the signals of the first amplifier 15 and the first
inverter 21, and a second inverter 20 reverses the phase of the output signal of the fourth
amplifier 18.
[0017]
22 is a second combiner for combining the signals of the third amplifier 16 and the second
inverter 20, 24 is an attenuator for attenuating the signal of the second combiner 22, 25 is a first
combiner 23 and A third synthesizer for combining the signals of the attenuators 24, a second
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inverter for inverting the phase of the signals of the attenuators 24, and a signal of the first
combiners 23 and a signal for the second inverters 26. The fourth combiner 28 combines the
second delay means 28 for delaying the signal of the fourth amplifier 18, and the inverter 29
reverses the phase of the signal for the second delay means 28.
[0018]
30 is a fifth synthesizer for synthesizing the signal of the second amplifier 16 and the signal of
the third inverter 29, 31 is a switch means for turning on / off the signal of the fifth synthesizer
30, 32 is a third A sixth synthesizer combines the signal of the combiner 25 and the signal of the
switch means 31, 33 is a seventh combiner that combines the signal of the fourth combiner 27
and the signal of the switch means 31, and 34 is the sixth An output terminal for outputting the
output signal of the combiner 32, an output terminal 35 for outputting the output signal of the
seventh combiner 33, and a switch 36 for determining on / off of the switch means 31.
[0019]
The case where the delay means 19 is constituted by a low pass filter is shown in FIG.
[0020]
Assuming that the distance between the microphone element 2 and the microphone element 1 in
FIG. 1 is l and a sine wave sin ωt is input as a sound source, the output signal of the microphone
element 1 is as follows: output signal a of the microphone element 1 The signal b is given by b =
sin (ωt + t1), where t1 represents the time difference at the distance l.
[0021]
Since the delay means uses the low-pass filter of FIG. 3, the output signal α of the first
combining means 23 is given by: α = sin ωt + K (sin ωt + t1 + ψ + π), where the phase
characteristic is ψ.
Further, the gain K of the low-pass filter given by the transfer function N / 1 + Ts is: K = 20 log (N
/ ((1+ (ωT) <2>)) The phase characteristic ψ is ψ = −arctan ωT Α = √ (A <2> + B <2>) sin (ωt
+ arctan B / A)
However, A = 1 + K cos (t1 + ψ + π) B = K sin (t1 + ψ + π)
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[0022]
In the equation giving this α, the incident angle of the sound source with the distance of the
microphone element l = 15 (mm), the passband gain N of the low pass filter N = 0.4, and the time
constant T of the low pass filter T = 4.6E <-5>. The result of computer simulation of a polar
pattern with a signal frequency of 1 kHz in which the wave length is shifted from 0 deg to 360
deg is shown in FIG.
As can be seen from FIG. 5, the characteristics are unidirectional, and constitute the mid
microphone of the MS microphone.
[0023]
Next, a characteristic generated by the microphone element 3 and the microphone element 4 is a
second synthesizer which is a signal obtained by inverting the phase of the output of the
microphone element 4 by the second inverter 20 with respect to the output of the microphone
element 3 Since the addition is performed at 22, when the signal picked up by the microphone
element 3 and the signal picked up by the microphone element 4 have the same phase
relationship, the synthesized signal is canceled and attenuated.
The condition for picking up the same signal is when the sound source is equidistant between the
microphone element 3 and the microphone element 4, and the position on a straight line
perpendicular to the line from the center of the line connecting the microphone element 3 and
the microphone element 4 is It becomes the maximum attenuation condition.
[0024]
FIG. 6 shows the result of computer simulation of the polar pattern in which the incident angle of
the sound source is changed from 0 deg to 360 deg in the same manner as described above.
As can be seen from the figure, the characteristics are bi-directional and constitute the side
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microphone of the MS microphone.
[0025]
As a result, the same signal processing as the MS microphone is performed on the two output
signals obtained with characteristics equivalent to the mid microphone and the side microphone
of the MS microphone.
Assuming that the signal of the mid microphone is M and the signal of the side microphone is S,
the respective channels, Lch and Rch are given by the following equations. Lch = (M + S) Rch =
(M−S) An equation giving the directional axis angle θ is: θ = 2 arctan 2K K = S / M
[0026]
The third synthesizer 25 adds up the signal S 'obtained by attenuating the level of the signal M of
the mid microphone which is the output signal of the first synthesizer 23 and the signal S of the
side microphone of the attenuator 24. In the fourth combiner 27, the signal M ′, which is the
output signal of the first combiner 23, the signal M of the mid microphone and the signal S ′
obtained by attenuating the level of the signal S of the side microphone of the attenuator 24 Add
the phase-inverted signal at. That is, the signal S 'obtained by attenuating the level of the signal S
of the side microphone from the signal M of the mid microphone, which is the output signal of
the first combiner 23, is subtracted. Therefore, the output signal of the third combiner 25 can be
represented by M + S '. Therefore, this signal becomes a left channel signal.
[0027]
The output signal of the fourth combiner 27 can be represented by M-S '. Therefore, this signal is
a right channel signal.
[0028]
The equation giving the directional axis angle θ as in the case of the MS microphone is θ = 2
arctan 2K K = S ′ / M, where the attenuation characteristic to give K = 0.15 is given to the 24
attenuators. The pointing axis angle θ of θ is θ = 60, and the polar pattern at that time is
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computer simulation results when the sound source direction is shifted from 0 to 360 degrees as
described above. Figure 7 shows the left channel and Figure 8 shows the polar pattern. Show.
[0029]
Next, signal processing by the microphone element 2 and the microphone element 4 will be
described.
[0030]
This is exactly the same as the signal processing of the microphone element 1 and the
microphone element 2 described above, and forms a unidirectional microphone having the
straight microphone element 2 connecting the microphone element 2 and the microphone
element 4 as the front, and the output signal thereof Is generated by the fifth synthesizer 30.
The characteristics are shown in FIG.
This shows the characteristic that the sensitivity in the direction of the mouth of the
photographer in FIG. 10 is high.
[0031]
The 32nd sixth combiner combines the signal of the switch means 31 and the output signal of
the third combiner 25. The seventh synthesizer 33 synthesizes the signal of the switch means 31
and the output signal of the fourth synthesizer 27. The switch means 31 is controlled by 36
switches in order to turn on / off the signal of the fifth combining means 30 and to limit the
input signal of the aforementioned sixth and seventh combiners.
[0032]
When the switch 36 is turned on, the switch means 31 is closed, and the signals of the fifth
combining means 30 are mixed with the signals of the sixth and seventh combining means into
the signals of the left and right channels. When the 36 switches are turned off, the 31 switch
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means becomes open, and the signals of the fifth combining means 30 are not mixed with the
input signals of the sixth and seventh combiners, and only the left and right channels are
signaled. It becomes.
[0033]
1 and 3 show Embodiment 2 of the present invention. In FIG. 3, the difference from FIG. 2 is only
in the portion where the input of the delay means 28 is 15 amplifiers and one of the inputs of the
synthesizer 30 is connected to the output of the amplifier 17. In the first embodiment, the
narration microphone is configured by the microphone elements 2 and 4 in FIG. 1, while in the
second embodiment, the narration microphone is configured by the microphone elements 1 and
3 in FIG. .
[0034]
The signal processing by the microphone element 1 and the microphone element 3 will be
described. This forms a unidirectional microphone whose front face is a straight microphone
element connecting the microphone element 1 and the microphone element 3 as described in the
first embodiment, and its output signal is generated by the fifth synthesizer 30. Be done. The
characteristics are the same as shown in FIG. Similarly to the first embodiment, this shows the
characteristic that the sensitivity in the direction of the mouth of the photographer in FIG. 10 is
high.
[0035]
It is a figure which shows arrangement | positioning of the microphone element of the Example
of this invention. It is a figure showing processing composition of Example 1 of the present
invention. It is a figure which shows the process structure of Example 2 of this invention. It is a
figure showing composition of LPF of the present invention. It is a polar pattern figure of a
unidirectional microphone. It is a polar pattern figure of a bi-directional microphone. FIG. 5 is a
diagram showing a polar pattern of the left channel according to the present invention. It is a
figure which shows the polar pattern of the right channel of this invention. It is a figure which
shows the polar pattern of the narration microphone of this invention. It is a figure which shows
the arrangement configuration of a prior art. It is a figure explaining the imaging condition of a
video camera.
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Explanation of sign
[0036]
11 to 14: Input terminals 15 to 18: Amplifiers 19, 28: Delay means 20, 21, 26: Inverters 22, 23,
25, 27, 30, 30, 32: Synthesizer
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