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DESCRIPTION JPH03278799

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DESCRIPTION JPH03278799
[0001]
FIELD OF THE INVENTION The present invention relates to an array microphone used as one of
directional microphones. 2. Description of the Related Art In recent years, an array microphone is
used as a sound collection means in an arbitrary direction or a means for suppressing howling of
a loudspeaker in a conference or the like. One of them is an array microphone which obtains
directivity by digital signal processing. Hereinafter, an example of the conventional array
microphone described above will be described with reference to the drawings. FIG. 4 shows the
configuration of a conventional array microphone. Reference numeral 41 denotes microphone
units constituting a microphone array, which are one-dimensionally arranged at an interval d. An
A / D conversion unit 42 converts each output of the microphone unit 41 into a digital signal. A
two-dimensional digital filter 13 performs a two-dimensional convolution operation on the
output of the A / D conversion means 42. Next, the operation of the array microphone shown in
FIG. 4 will be described. Two-dimensional signal processing on the space axis and the time axis is
performed on the input signal obtained from the microphone array of the interval d of the
microphone unit 41 by the above-described configuration. That is, assuming that the angle ? of
the array direction of the microphone array is ? = 01, the frequency spectrum of the sound
wave observed by this microphone array is the time frequency f1 due to the signal from the
microphone array being temporally sampled. On a two-dimensional frequency plane represented
by two orthogonal frequency axes with the spatial frequency f2 due to the spatial sampling of the
microphone array, fz ''-d-cos (?) / (Tc) .f + ''. ... (1) where (, 1 ? ? two-time frequency
(normalized frequency) ft: spatial frequency (normalized frequency) T: sampling period d:
microphone unit interval C: appearing on the speed of sound. Here, assuming that the passband
of the two-dimensional filter is, for example, a region represented by f2> If, l or f, X f2> 0... -.- (2)
on a two-dimensional frequency plane, a microphone The sound collection region of is -c o 5 ((Tc
/ d) ? ? c cs' (Tc / d)) (3). If the passband of the two-dimensional digital filter is flat and the cut-
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off zone is sharp, the sensitivity is negative for any angle in the sound collection area, and the
boundary between the dead area and the sound collection area has a clear directivity
characteristic. Further, since the equation (2) does not include a variable related to frequency, the
directivity characteristic does not depend on frequency. When the sampling period is changed, ?
satisfying the equation (2) changes, so that the angle of the sound collection region changes.
For example, if the passband of the two-dimensional digital filter is changed, the directivity
pattern changes. For example, the passband of the two-dimensional filter is represented by f21
? 1f11 (4) on the two-dimensional frequency plane. If the sound collection area of the
microphone is 90?-cos ((T?C / d) ? ? ? 90 @ + cos ? ? (T?C / d) 270 ░ ?cos?I (T?C /
d) ? ? ? 270 ░ + cos ? (T?C / d) (5) FIG. 5 is a polar pattern of the output of the array
microphone by the two-dimensional filter having the passband represented by the equation (2).
Thus, directivity can be obtained even with the array microphone according to the abovedescribed conventional configuration. SUMMARY OF THE INVENTION However, in the
configuration as described above, it is necessary to increase the order of the two-dimensional
digital filter in order to obtain the directivity characteristics in a wide band. In the following
description, the frequency band having the directivity characteristic is called a directivity band.
FIG. 6 is a graph in which the directional band is represented by an octave and the relationship
with the filter order is represented. Further, since the number of taps of the two-dimensional
digital filter is the square of the order, the hardware becomes very large as the order increases.
From the above facts, in the configuration as described above, in order to obtain the directivity
characteristics in a wide band, there is a disadvantage that very large hardware is required.
SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks, the present
invention makes it possible to obtain the directivity characteristics in a wide band with a small
number of taps, and make the hardware small-scale and inexpensive, and the present invention
aims to solve the above-mentioned problems. The frequency band is divided into a plurality of
bands, and a narrow band array microphone is configured for each band, and their outputs are
added. Based on this means, the present invention comprises a plurality of narrow band sound
collecting means, and an adding means for adding the output signals of the plurality of narrow
band sound collecting means to obtain a wide band signal. Further, the narrow band sound
collecting means is a two-dimensional output signal of the analog / digital conversion means, a
microphone array in which a plurality of microphone units are linearly arranged, an analog /
digital conversion means provided for each of the plurality of microphone units. A plurality of
two-dimensional digital filters for performing convolutional summer output, sampling period
conversion means for converting the sampling period of the output signal of the two-dimensional
filter, and group delay time for the output signal of the two-dimensional digital filter A delay
means, and a plurality of band pass digital filters for passing a frequency band having directivity
among the output signals of the sampling period conversion means and the delay means are
constituted.
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And the ratio of the spacing of the microphone unit to the corresponding sampling period is set
equal, and all the microphone arrays are arranged on the same straight line and the positions of
the middle points thereof are all equal in space. There is. Also, the sampling period converting
means and the delaying means adjust the sampling period and the group delay time of the output
signals of all the narrow band sound collecting means equally, and the two-dimensional digital
filter and the band pass digital filter All have linear phase characteristics. In this configuration,
each of the plurality of narrow band sound pickup means is constituted by an array microphone
based on the same principle as that of the conventional example and a band division digital filter
for extracting a frequency band having directivity. A wide band output can be obtained by adding
the outputs of the narrow band sound pickup means for all bands. The reason why the number of
taps is small in the present invention will be described. In the configuration according to the
present invention, the frequency band required for each two-dimensional digital filter is narrow,
so the filter may be of low order, and the number of taps of the two-dimensional filter is the
square of the order. The number is significantly reduced compared to the prior art. Also, since
the band pass digital filter is a one-dimensional filter, the number of taps is not very large. From
the above, although the number of filters in the entire array microphone is increased compared
to the prior art, the number of required taps is decreased compared to the prior art. Next, the
directional characteristics of the array microphone of the present invention are All. The ratio of
the microphone unit spacing of the microphone array to the sampling period of the analog-todigital conversion means downstream thereof is the same for any narrow-band sound collection
means. Substituting this into the equation (3), it can be understood that the sound collection area
? becomes equal in any band. Therefore, the sound collection area is equal in all the target
frequency bands. In addition, frequency characteristics will be described. In order to obtain flat
characteristics in each band, a two-dimensional filter having a flat pass band may be used in each
narrow band sound collection means. Here, since there is no difference in group delay spatially
and temporally between each narrow band sound collecting means, and furthermore, since the
two-dimensional digital filter and the band pass filter are all in linear phase, the output of each
narrow band sound collecting means The characteristics are not disturbed by adding. Therefore,
it is possible to obtain continuous and flat characteristics over the entire frequency band. From
the above, according to the present invention, the directivity characteristic can be obtained in a
wide band by a small number of taps.
As a result, the hardware can be made small and inexpensive. Further, the directivity pattern can
be changed by changing the coefficients of each two-dimensional digital filter. Also, if the
sampling period of each analog / digital conversion means is changed, and at the same time the
coefficients of each channel division digital filter are changed so that the cutoff frequency does
not change, the directivity pattern remains as it is. It can be changed. Also, if the coefficients of
each two-dimensional digital filter are equalized, uniform directional characteristics can be
obtained in all frequency bands. When the positions of the ?S microphone units in the plurality
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of microphone arrays coincide, the number of microphone units can be reduced by sharing the
microphone units by a plurality of channels. EXAMPLES The first embodiment of the present
invention will be described with reference to the drawings. FIG. 1 shows the configuration of an
array microphone according to a first embodiment of the present invention. In FIG. 1, 1 is a high
frequency array microphone, 2 is a low frequency array microphone, and 3 is an adder. In the
high frequency array microphone 1, 11 is a microphone unit linearly arranged at an interval dH,
15 is a high frequency microphone array, 12 is an A / D conversion means, 13 is a twodimensional digital filter of linear phase characteristics, and 14 is a delay. 16 is a linear phase
characteristic band pass digital filter (BPF). In the low-range array microphone 2, 21 is a
microphone unit linearly arranged at an interval dL, 24 is a low-range microphone array, 22 is an
A / D conversion means, 23 is a two-dimensional digital filter of linear phase characteristics, 25
is interpolation , 26 is a linear phase characteristic band pass digital filter (BPF). The microphone
arrays 15.24 are arranged on the same straight line so that the positions of their midpoints are
all equal in space. The unit interval dH5 of the high-range microphone array I5, inter-unit Fild L
of the low-range microphone array 24, the sampling period TH of the A / D conversion means I2,
the sampling period TL of the A / D conversion means 22 Is set to be dH H dL (6) and T, 4 dH-(7)
TL dL. The operation of the array microphone configured as described above will be described
below. In this microphone, the frequency band for performing directional sound collection is
divided into a high band and a low band.
Then, the directional sound collection is performed by the high frequency array microphone 1
and the low frequency array microphone 2, and the outputs thereof are added by the adder 3 to
obtain directivity in a wide band. The operation of each array microphone will be described
below. First, the operation of the high frequency array microphone 1 will be described. The A / D
conversion means 12 converts the sound waves picked up by the microphone unit 11 into digital
signals at a sampling period TH. The two-dimensional digital filter 13 performs two-dimensional
convolution processing on this signal, forms directivity based on the same principle as the
conventional example, and outputs it. For this output, the delay 814 provides group delay to
make the group delay equal to the low band, and the bandpass digital filter 16 passes only the
directivity band. Next, the operation of the low-range array microphone 2 will be described. The
A / D conversion means 22 converts the sound waves picked up by the microphone unit 7) 21
into digital signals at a sampling period TL. The two-dimensional digital filter 23 performs twodimensional convolution processing on this signal, forms directivity based on the same principle
as the conventional example, and outputs it. At this time, the directional band is a frequency band
lower than that of the two-dimensional digital filter 13 from the relationship of the equation (6).
For this output, the interpolator 25 converts the sampling period to T8, and the bandpass digital
filter 26 passes only the directivity band. The two-dimensional digital filter of the array
microphone of each band has the lower limit of the directivity band given by the two-dimensional
digital filter 13 and the high limit given by the two-dimensional digital filter 23 coincident with
each other. At this time, when the outputs of the band pass digital filter 16 and the band pass
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digital filter 26 are added by the adder 3, the directivity band thereof is the frequency band of
the high frequency array microphone 1 and the low frequency array microphone 2. It becomes.
As described above, according to the first embodiment, the directivity can be obtained in a wide
band by a small number of taps. Hereinafter, a second embodiment of the present invention will
be described with reference to the drawings. FIG. 2 shows the configuration of an array
microphone according to a second embodiment of the present invention. The same reference
numerals as in FIG. 1 denote the same parts as in FIG. 1, and a detailed description thereof will be
omitted. The unit interval dL of the unit interval dH1 for the low range microphone array 15 of
the high range microphone array 15, the sampling interval TH of the A / D conversion means 12,
and the sampling period TL of the A / D conversion means 22 are described above. (6) It is set to
satisfy the equation (7).
The difference from the configuration of FIG. 1 is that a coefficient changing means 4 of a twodimensional filter is provided. The operation of the array microphone configured as described
above will be described below. The operation other than the coefficient changing means 4 of the
two-dimensional filter is the same as that of the first embodiment. In this embodiment, the
directivity pattern of the array microphone can be changed by changing the coefficients of the
two-dimensional digital filter by the coefficient conversion means 4 of the two-dimensional filter.
As described above, according to the second embodiment, in addition to the effects of the first
embodiment, the directivity pattern of the array microphone can be changed. Hereinafter, a third
embodiment of the present invention will be described with reference to the drawings. FIG. 3
shows the configuration of an array microphone according to a third embodiment of the present
invention. The same reference numerals as in FIG. 1 denote the same parts as in FIG. 1 and their
detailed description will be omitted. The unit interval dL of the unit interval dH1 for the low
range microphone array 15 of the high range microphone array 15, the sampling interval TH of
the A / D conversion means 12, and the sampling period TL of the A / D conversion means 22
are described above. (6) It is set to satisfy Formula 2 (7). What differs from the configuration of
FIG. 1 is that sampling period changing means 5 and coefficient changing means 6 for banddivision digital filters are provided. The operation of the array microphone configured as
described above will be described below. The operation other than the sampling period changing
means 5 and the coefficient changing means 6 of the band division digital filter is the same as
that of the first embodiment. In this embodiment, an array is obtained by changing the sampling
period TH of the A / D conversion means 12 and the sampling period TL of the A / D conversion
means 22 while the sampling period changing means 5 satisfies the equation (7). The angle of
the sound collection area of the microphone can be changed. At this time, the directivity band of
the two-dimensional digital filter 13.23 does not change, but the pass band of the band-resolved
digital filter 16.26 changes with the change of the sampling period. Therefore, the coefficients of
the band division digital filter 16.26 are changed by the coefficient changing means 6 of the
band division digital filter to make the pass band equal to that before the change. As described
above, according to the third embodiment, the first actual! In addition to the example effect, the
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angle of the sound collection area of the array microphone can be changed. In the above
embodiment, if the coefficients of the two-dimensional digital filter 13.23 are made equal, the
frequency characteristics of the low frequency array microphone 2 are converted to TH / TL
times the frequency by the frequency characteristics of the high frequency array microphone 1
Since the characteristics are the same, uniform characteristics can be obtained in the low and
high regions.
In the above embodiments, when the positions of some of the microphone units coincide with
each other in the low range and high range microphone arrays, the number of microphone units
can be reduced by sharing the microphone units in the low range and the high range. can do. As
described above, the present invention comprises a plurality of narrow band sound collecting
means, and addition means for adding the output signals of the plurality of narrow band sound
collecting means to obtain a wide band signal, the narrow band sound pickup Means, a
microphone array in which a plurality of microphone units are linearly arranged, an analog /
digital conversion means provided for each of the plurality of microphone units, and a twodimensional operation for performing two-dimensional convolution operation on output signals
of the plurality of microphone units Digital filter, sampling period converting means for
converting sampling period of output signal of said two-dimensional filter, delay means for giving
group delay time to output signal of said two-dimensional digital filter, said sampling period
converting means, And a plurality of band pass digital filters for extracting frequency band
components of the output signal of the delay means. The ratio of the interval between the
microphone units and the corresponding sampling period is set equal, and all the microphone
arrays are arranged on the same straight line and the positions of the middle points thereof are
all equal in space, the sampling period conversion The sampling period and the group delay time
of the output signals of all the narrow band sound pickup means are adjusted to equal values by
the means and the delay means, and all linear phase characteristics of the two-dimensional
digital filter and the band pass digital filter are adjusted. By using the above, it is possible to
obtain directivity characteristics with a clear blind boundary between the dead area and the
sound collecting area in a wide band with a small number of taps with any sensitivity at any
angle in the sound collecting area.
[0002]
Brief description of the drawings
[0003]
1 is a block diagram of an array microphone according to a first embodiment of the present
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invention, FIG. 2 is a block diagram of an array microphone according to a second embodiment
of the present invention, and FIG. 3 is a third embodiment of the present invention 4 is a block
diagram of the conventional array microphone, FIG. 5 is a polar pattern of the array microphone
[21, FIG. 6 shows the relationship between the directivity band and the filter order of the
conventional array microphone It is a graph.
3 ...... adders, the coefficient changing means 4 ...... two-dimensional filter, the sampling period
changing means, the coefficient change means of the band-pass digital filter, 11.21 ......
microphone Unit, 12.22 ииииии A / D conversion means, 13.23 и и и и и Two-dimensional digital filter, и и
и и и и и и и и и и и и и и и и и и и и Interpolator , 16.26 ..... band pass digital filters
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