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JPH04309097

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DESCRIPTION JPH04309097
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
directional microphone systems, and more particularly to signal processing techniques for
directional microphones. For example, it is applied to a microphone system for a video camera
and a microphone system for a voice recognition device.
[0002]
2. Description of the Related Art In general, microphones with a sharp directivity include
microphones using paraboloidal sound collectors, line microphones (gun microphones), and highorder sound pressure gradient microphones. For microphones using a parabolic sound collector,
sharp directivity can be obtained in the high region, but in order to obtain the effect in the low
region, the diameter of the paraboloid must be increased to about 70 cm. It is not suitable for
general use. With regard to line microphones as well, sharp directivity can be obtained in the
high region, but in order to obtain effects in the low region, the length of the acoustic tube must
be as long as about 40 cm, which is unsuitable for general applications. is there. With regard to
the high-order sound pressure gradient microphones, directivity characteristics independent of
the band can be obtained, but the gain in the low range is attenuated. If the order is increased to
obtain sharp directivity, the attenuation in the low band increases by -6 dB / oct per order, and
the usable band width becomes extremely narrow, which is not practical.
[0003]
03-05-2019
1
As a prior art related to superdirective microphones, there is, for example, the one disclosed in
JP-A-59-70097, which uses a plurality of microphone units arranged on a straight line, and an
acoustic time according to the distance between each unit The delay is equal to the time delay
and the total addition is basically the same principle as the line microphone, and in order to
obtain the effect in the low range, the length of the acoustic tube must be increased. There is a
point. In addition, the method disclosed in Japanese Patent Application Laid-Open No. 59-70097
compensates for the low-pass attenuation by combining two secondary sound pressure gradient
microphones, but basically the secondary sound pressure is reduced. Since the gradient type is
used, the directivity characteristic does not exceed the secondary sound pressure gradient type
characteristic (-8.5 dB at an angle of 60 degrees).
[0004]
[Purpose] The present invention has been made in view of the above-described circumstances,
and it is an object of the present invention to provide a microphone system which has a relatively
small shape and sharp directivity for all voice bands. It is.
[0005]
According to the present invention, in order to achieve the above object, (1) a plurality of
microphone units arranged in a straight line and a plurality of subtractions performed using the
output of the microphone unit And second signal processing means for performing addition after
each predetermined delay using the output of the microphone unit, and at least an output of the
first signal processing means and the second signal processing means. (2) in (1), the first signal
processing means is N-order (N is an integer of 3 or more). Obtaining the characteristics of the
sound pressure gradient type microphone, and obtaining the characteristics of the line
microphone by the second signal processing means; and (3) in the above (1) or (2), the
synthesizing means is a low pass transmission filter Obtained using And combining the low-pass
component of the output of the first signal processing means with the high-pass component of
the output of the second signal processing means obtained using a high pass filter. .
Hereinafter, the present invention will be described based on an embodiment of the present
invention.
[0006]
03-05-2019
2
FIG. 1 is a block diagram for explaining one embodiment of a directional microphone system
according to the present invention, in which 10 to 17 are microphone units, 21 to 27 are delay
elements, 30, 31, 32 are The adders 40 and 41 are equalizers, 50 and 51 are low pass filters
(LPF), 52 is a high pass filter (HPF), 60, 61 and 62 are amplifiers, and 70 is an adder. The
microphone units 10 to 17 are arranged on a straight line at equal intervals d. The microphone
unit 17 is at the end and the microphone unit 10 is at the end. It is assumed that the target
sound comes from the tip direction (0 degree) on the straight line where the microphone unit is
disposed. These microphone units all have the same characteristics, directivity is a cardioid with
maximum sensitivity in the 0 degree direction, and frequency characteristics are assumed to be
flat with respect to the voice band to simplify the description.
[0007]
The adder 30 adds the output signals of the microphone units 10, 11, 16 and 17 and subtracts
the output signals of the microphone units 12, 13, 14 and 15. The characteristic of this output
signal is similar to that of the third-order sound pressure gradient type and has a fairly sharp
directivity, but has a low attenuation of -12 dB / oct and a narrow usable band. The adder 31
adds the output signals of the microphone units 11, 12, 14, 17 and subtracts the output signals
of the microphone units 10, 13, 15, 16. The characteristic of this output signal is a fourth-order
sound pressure gradient type characteristic, and it has sharp directivity, but attenuation of −18
dB / oct and a narrow band which can be used.
[0008]
The delay circuits 21 to 27 respectively delay the output signals of the microphone units 11 to
17 by τ, 2τ, 3τ, 4τ, 5τ, 6τ, 7τ, respectively. However, the delay time τ = d / c. The adder
32 adds the output signal of the microphone unit 10 and the output signals of the delay circuits
21 to 27. The characteristic of this output signal is a characteristic obtained by multiplying the
output of the line microphone by the cardioid, and it has flat frequency characteristics and sharp
directivity in the high region, but the directivity in the low region is not sharp.
[0009]
03-05-2019
3
From the advantages and disadvantages of the output signals of the adders 30, 31 and 32,
respectively, the output of the adder 30 is for low frequency, the output of the adder 31 is for
mid frequency, and the output of the adder 32 is for high frequency. Used in combination. The
equalizer 40 equalizes low-pass attenuation to the output signal of the adder 30 with a secondorder Butterworth-type low-pass filter with a cutoff frequency fc0. The low pass filter 50 cuts the
high frequency band of the output signal of the equalizer 40 with a second order Butterworth
low pass filter having a cutoff frequency fc1. This output signal has good directivity and flat
frequency characteristics in the band between fc0 and fc1. The equalizer 41 equalizes the lowpass attenuation to the output signal of the adder 31 with a third-order Butterworth low-pass
filter with a cutoff frequency fc1.
[0010]
The low pass filter 51 cuts the high frequency band of the output signal of the equalizer 41 with
a third order Butterworth low pass filter having a cutoff frequency fc2. This output signal has
good directivity and flat frequency characteristics in the band between fc1 and fc2. The high pass
filter 52 blocks the low frequency band of the output signal of the adder 32 with a third-order
Butterworth high-pass filter having a cutoff frequency fc2. The output signal has good directivity
and flat frequency characteristics in a band of fc2 or more. The amplifiers 60, 61, 62 adjust the
levels of the output signals of the low pass filter 50, the low pass filter 51, and the high pass
filter 52, respectively, to equalize the front sensitivity of the low, middle and high frequencies.
The amplification factors are A0, A1 and A2, respectively.
[0011]
The adder 70 subtracts the output signals of the amplifiers 60 and 61 and adds the output
signals of the amplifier 62. This output signal is the output of the microphone system of the
present invention, and good directivity characteristics and flat frequency characteristics can be
obtained in a band of fc0 or more. Here, FIGS. 3A to 3C show the frequency characteristics of the
plane wave when the microphone spacing d = 25 mm, the cutoff frequency fc0 = 200 Hz, the
cutoff frequency fc1 = 600 Hz, and the cutoff frequency fc2 = 2500 Hz, The directional
characteristics are shown in FIGS. 4 (a) to 4 (f).
[0012]
03-05-2019
4
3 (a) is a frequency characteristic diagram in the 0 degree direction, FIG. 3 (b) is a frequency
characteristic diagram in the 60 degree direction, and FIG. 3 (c) is a frequency characteristic
diagram in the 90 degree direction. 4 (a) is a directivity characteristic diagram for 250 Hz, FIG. 4
(b) is a directivity characteristic diagram for 500 Hz, FIG. 4 (c) is a directivity characteristic
diagram for 1 kHz, FIG. 4 (d) is a directivity characteristic diagram for 2 kHz, FIG. e) is a
directivity characteristic diagram for 4 kHz, and FIG. 4 (f) is a directivity diagram for 8 kHz.
According to these, it is understood that directivity of -12 dB or less at an angle of 60 degrees
and -15 dB or less at a range of 90 degrees to 180 degrees can be obtained in a band of 200 Hz
to 8 kHz.
[0013]
FIG. 2 is a diagram showing the hardware configuration for realizing the directional microphone
system according to the present invention, 100 to 107 being a microphone amplifier, 110 to 117
being a sample hold, 120 being a multiplexer, 130 being an A / D. The converter 140 is a digital
signal processor (DSP). The microphone amplifiers 100 to 107 perform amplification and high
frequency cutoff of the respective outputs of the microphone units 10 to 17. The sample and
hold 110 to 117 sample and hold each output of the microphone amplifiers 100 to 107 at the
same timing (sampling frequency 16 kHz). The multiplexer 120 multiplexes each output of the
sample and hold 110-117.
[0014]
A / D converter 130 converts the output of multiplexer 120 into digital values. The DPS (digital
signal processor) 140 applies the above-described adders 30, 31, 32, equalizers 40, 41, low pass
filters 50, 51, high pass filters to the output signals from the respective microphones obtained by
the A / D converter 130. 52, the processing of the amplifiers 60, 61, 62 and the adder 70 is
performed by digital signal processing.
[0015]
[Effect] As is apparent from the above description, according to the present invention, the
directivity in the low region is excellent by using the microphone units of multiple colors
arranged in a straight line and the outputs of the above microphone units. N = N (N is an integer
greater than 3) Next line pressure characteristics with good directivity in the high region are
obtained using the output obtained by processing to obtain the next sound pressure gradient
type characteristics and the output of the above microphone unit Since the processed output is
03-05-2019
5
combined, good directional characteristics can be obtained over the entire voice band.
[0016]
Brief description of the drawings
[0017]
FIG. 1 is a configuration diagram for explaining an embodiment of a directional microphone
system according to the present invention.
[0018]
Figure 2 is a hardware configuration diagram.
[0019]
FIG. 3 is a diagram showing frequency characteristics.
[0020]
FIG. 4 is a diagram showing directivity characteristics.
[0021]
Explanation of sign
[0022]
10-17: Microphone unit, 21-27: Delay element, 30, 31, 32: Adder, 40, 41: Equalizer, 50, 51: Low
pass filter (LPF), 52: High pass filter (HPF), 60, 61 , 62 ... amplifier, 70 ... adder.
03-05-2019
6
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