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JPH0591588

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DESCRIPTION JPH0591588
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
directional sound pickup apparatus for selectively picking up sound waves from a sound source
in a specific direction.
[0002]
2. Description of the Related Art A directional sound pickup system using a microphone array
and simultaneously weighted averaging the output analog signals has the advantage of being
able to selectively collect only sound waves from near the direction perpendicular to the axis of
the microphone array. Therefore, it is put to practical use in the field such as search for noise
sources. (Directivity Sound Collection Device, Patent Publication Sho 57-31353 (JP, B2)) FIG. 2
illustrates the configuration of a conventional directivity sound collection device using a
microphone array. M0, M1, M2,... Mn, M-1, M-2,..., Mn are 2n + 1 element microphones W0, W1,
W2 disposed at an interval d on the axis 1 of the microphone array ,... Wn, W-1, W-2,..., Wn are
weights applied to the respective output signals, and the weighted average output signal
obtained by adding the weighted outputs through the analog addition circuit 8 is an octave band
Filter by filter 9 to obtain a directional output signal. That is, since the planar sound waves
arriving perpendicularly to the axis 1 of the microphone array are in phase with all the element
microphones, the amplitude of the directional output signal is maximized, while the wavelength
2d of the wavelength coming from the direction of the axis 1 of the microphone array Since the
plane acoustic wave is in opposite phase at the adjacent element microphones, the amplitude of
the directional output signal is minimized, and the directional characteristic having the highest
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sensitivity in the direction perpendicular to the axis of the microphone array is formed.
[0003]
However, since the direction of directivity is fixed to the axis 1 of the microphone array, there is
a drawback that it can not be changed.
[0004]
Therefore, in the case of obtaining the intensity distribution of a sound source which is
temporally steady and spatially distributed, a method of repeatedly measuring by changing the
installation angle of the microphone array in order to change the direction of directivity, and time
In the case of measuring temporal variation of the intensity distribution of sound sources that are
spatially fluctuating and spatially dispersed, there is a method of simultaneously using multiple
microphone arrays with different installation angles, but the former The operation is
complicated, and the latter has problems such as having to use a large number of devices.
[0005]
The problem to be solved is that the pointing direction is fixed perpendicular to the axis of the
microphone array and can not be changed.
[0006]
SUMMARY OF THE INVENTION According to the present invention, in order to make the
pointing direction variable, it is essential to perform averaging by shifting the output of each
element microphone by a time difference determined by the position of each element
microphone and the pointing direction to be set. It features.
The operation of shifting the output of each element microphone by an arbitrary time difference
is easily realized by converting digital time series data obtained by simultaneously AD converting
the output of each element microphone.
[0007]
The principle of the present invention is shown in FIG. 3 when the number of element
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2
microphones is three.
Considering the case where the axis 1 of the microphone array is rotated by an angle θ around
M 0, the directivity direction is the microphone when the axis 11 'perpendicular to the axis of the
microphone array is rotated by an angle θ It is a plane rotated about the axis 1 'of the array.
The element microphones at this time are M1 'and M-1'. Considering the virtual element
microphones M1 "and M-1" on the point of intersection with the perpendicular drawn to the axis
1 'of the microphone array when the angle θ is rotated from M1 and M-1, the rotation angle θ
is so large Unless the position of M1 ', M-1' is close to the position of M1 ", M-1", the former
output can be approximated by the latter output. Here, considering an incident sound wave from
a direction perpendicular to the axis 1 of the microphone array when the angle θ is rotated in
the plane of the axis 1 of the microphone array when the axis 1 of the microphone array and the
angle θ are rotated, M1 ′ ′ The outputs of the original element microphones M1 and M-1
coincide with those obtained by shifting the intervals L1 and L-1 of the original element
microphones M1 and M-1 by the time when the sound wave propagates. That is, for sound waves
coming from within a specific plane including the axis 1 of the microphone array, the operation
of rotating the axis 1 of the microphone array in the plane where the sound waves arrive to
change the pointing direction is the element microphone M1, This operation is approximately
equivalent to the operation of shifting the output of M-1 by a specific time, which makes it
possible to make the pointing direction variable without actually rotating the axis 1 of the
microphone array. The operation of shifting the time of the output of the element microphone is
approximately equivalent to the operation of rotating the axis 1 of the microphone array within
the plane of incidence of the sound wave, so the directivity direction with the highest sensitivity
is rotated by the angle θ The axis 1 of the microphone array is a conical surface rotated around
the axis 1 of the microphone array.
[0008]
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram of one
embodiment of the present invention, wherein M0, M1, M2,... Mn, M-1, M-2,. The element
microphones are arranged at equal intervals d on the axis of. 2 is a multi-channel simultaneous
AD converter, 3 is a parameter input unit included in the program, 4 is a digital computer, 5a, 5b,
5c are programs installed in the computer, 6 is an analog output 7 Is a DA converter for
[0009]
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A multi-channel simultaneous AD converter 2 is a sampling period that sufficiently reproduces
the highest frequency to be analyzed of the analog signals of the element microphones M0, M1,
M2, ... Mn, M-1, M-2, ... AD conversion is performed by τ and supplied to the digital computer 4.
[0010]
The parameter input unit 3 includes the number 2 n + 1 of element microphones, the installation
interval d, the weighted average weights W0, W1, W2, ... Wn, W-1, W-2, ... W-n, the speed C of
the sound wave Of the pointing direction, etc. are given to the computer.
[0011]
The function of the program 5a mounted on the computer is as follows: from the installation
interval d of the element microphones, the velocity C of the sound wave, and the angle θ of the
pointing direction, each element microphone M0, M1, M2, ... Mn, M-1, M-2, Calculate the time
difference given to the digital time series obtained from Mn, and generate new time series data
given the time difference.
Taking the element microphone M0 as a reference, the time difference Ti given to the output of
each element microphone M0, M1, M2, ... Mn, M-1, M-2, ... Mn is
[0013]
Calculated using:
Here, Ti is the delay time given in time series from the element microphone Mi (i = 0, ± 1,... N), d
is the installation interval of the element microphone, C is the speed of the sound wave, and θ is
the sensitivity This is the angle of the pointing direction that is maximized. When Ti is an integral
multiple of the sampling period τ of AD conversion, new time-series data given a time difference
can be easily generated by shifting the original time-series data by the integer number. When Ti
is not an integral multiple of the sampling period τ of AD conversion, new time series data given
a time difference is generated by interpolating and obtaining the value of the time delayed Ti
from the original time series data.
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[0014]
The functions of the program 5b installed in the computer are the new time-series data given the
time difference obtained by the program 5a installed in the computer, and each element
microphone M0, M1, M2, ... Mn, M-1, M- 2,... Weights W0, W1, W2,... Wn, W-1, W-2,. Generate
one time series data.
[0015]
The function of the program 5c installed in the computer is a digital band pass filter, and passes
only a specific frequency band component of time series data of directivity output obtained by
the program installed 5b in the computer.
Passing frequency band is
[0017]
It is an octave band whose center frequency is f 0 calculated by Here, d is the installation interval
of the element microphone, and C is the velocity of the sound wave.
[0018]
The DA converter 6 converts the digital time-series data of directional output filtered by the
program 5c installed in the computer into an analog signal, and supplies the analog signal to an
acoustic measuring instrument such as a commonly used level recorder.
[0019]
FIG. 4 shows the results of calculation of the directivity characteristics for a sinusoidal sound
wave of wavelength 2d by changing the directivity direction when the method of the present
invention is applied as the number of element microphones is octave band filter 9 and weight W
is Table 1. It is a thing.
[0021]
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The directivity direction of 0 degrees has a delay time of 0, which is the same characteristic as
that of the conventional directional sound collecting apparatus.
The directivity in the case where the directivity direction is set within about 40 degrees is similar
to the directivity in which the directivity direction is 0 degree shifted from the set angle, and it is
confirmed that the directivity direction can be changed without losing the directivity. .
However, it can be seen that the directivity characteristics when the directivity direction is set
within about 40 degrees is wider than the directivity characteristics of the directivity direction 0
degree, and the sensitivity is also high for incident sound waves from the opposite direction. That
is, according to the method of the present invention, it is possible to set an arbitrary pointing
direction within a certain range without losing the directivity.
[0022]
Although the case where the number of element microphones is an odd number is shown in the
embodiment, the same method can be applied by changing the calculation formula of the delay
time also in the case of an even number.
[0023]
As described above, according to the variable directivity directivity sound pickup apparatus of
the present invention, the same operation as changing the direction of the microphone array is
performed by temporally shifting the outputs of the element microphones, and By adopting a
method to shift the time arbitrarily and easily by converting digital time series obtained by AD
conversion, it is possible to direct the pointing direction to any direction within a certain angular
range without impairing the directivity characteristic. There is an advantage.
In addition, since the pointing direction can be set by a program of a computer, the present
invention can also be applied to applications in which directivity output of multiple pointing
directions can be obtained from one recorded data by repeatedly executing the program.
Furthermore, in the conventional directional sound pickup apparatus based on analog signal
processing, variations in sensitivity of the element microphones and variations in constants of the
resistance elements giving the weighting factor greatly affect the directivity characteristics, so
these are adjusted to the design values There is a problem in terms of manufacturing process and
manufacturing cost, such as selecting one having many characteristics matching among many
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parts, but in the case of digitally performing signal processing as in the present invention, these
Since the variation is easily realized by the correction of the weighting factor, there is an
advantage that it is easy to obtain a theoretical directional characteristic.
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