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JPH0884392

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPH0884392
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
each microphone when a plurality of microphones are used to receive a focused sound (a point to
be noted) mainly in a reverberant sound field such as a hall or a speech communication
conference. The present invention relates to a sound receiving method called delay sum array,
and its apparatus for giving time delays to the output signals of the microphones according to
the distance from the focal point to the respective microphones and extracting the output sums
of the respective microphones.
[0002]
2. Description of the Related Art The principle of a delay and sum array will be described with
reference to FIG. FIG. 3 shows a sound receiving apparatus using two sets of circumferentiallyarranged microphone arrays 11 and 12. In FIG. 3, 2 is a microphone holding frame, 31, 32, ...,
3M are microphones, 41, 42 ..., 4M are delayers, 5 is an adder, and 6 is an output signal.
[0003]
The delay unit 4i (i = 1 to M) adds a delay amount Di shown by the following equation to the
output signal yi of the microphone 3i. Di = D0-τi; i = 1, 2, ... M (1) τi = ri / c ... (2) where M is
the number of microphones, ri is the distance from focal point P to microphone 3i, and c is
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1
Represents the speed of sound. D0 is a fixed delay amount to be added to prevent the delay
amount Di from being too small and the accuracy in realizing the delay characteristic with a
digital filter being lowered.
[0004]
The target signal corresponding to the sound of focus is represented by a complex sine wave
signal (exp (jωt)). Then, it is assumed that this target signal arrives at each microphone directly
from the focal position. At this time, the magnitude of the target signal yi (t) received by the
microphone 3i is inversely proportional to the distance ri, and its phase is delayed by τi = ri / c
(seconds), so yi (t) = (1 / ri). ) exp (jω (t-τi)) ...... (3)
[0005]
Since the output of the delay amount 4i is a signal yi (t-Di) obtained by adding the delay amount
Di to each sound receiving signal yi (t), the equation (1) is substituted into the equation (3), yi (tDi) = (1 / ri) exp (j? (t-? i-Di)) = (1 / ri) exp (j? (t-D0)) (4). As can be seen from this equation, the
outputs yi (t-Di) from the respective delay devices 3i (i = 1, 2,... M) are signals of the same phase
regardless of the channel number i. In other words, it is understood that the delay operation
corrects the time difference of the signals coming from the focal point position to be in phase.
Then, by adding the in-phased signals in the adder 4, the sounds coming from the focal point P
are coordinated. On the other hand, the sound coming from the direction different from the focal
point P is received with a propagation time τNi different from τi. Therefore, in the delay
operation according to Di expressed by the equation (4), the signals are not in phase, and the
outputs of the delay elements have waveforms which are shifted in time, and even if they are
added, the coordination effect is small. As a result of the above, the delay-and-sum array forms a
directional pattern with high sensitivity only in the focal direction.
[0006]
In FIG. 3, consider the case where 16 microphones are attached to each of two sets of
circumferentially-arranged microphone arrays 11 and 12 and a delay amount Di is added. At this
time, the absolute value of the output signal of the adder 6 for the sound source placed at an
arbitrary position is given by the following equation.
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[0007]
Here, ξi represents the distance from an arbitrary position to the microphone 3i. Fig. 4 shows
the two microphone arrays 11 and 12 shown in Fig. 3 suspended from the ceiling in a room 6.8
m wide, 4.2 m long and 3.1 m high, 1.1 m below the microphone array The simulation results of
the sensitivity distribution of Specifically, contours are calculated by calculating from the output
magnitude formula (5) for the sound source placed at each point. In the calculation, a free sound
field was assumed, and the average was obtained at an average of 11 points (310 Hz intervals) of
300 Hz to 3.4 kHz. The two sets of microphone arrays 11, 12 are arranged around ps2 and ps5
in FIG. 4, and the focus of the array is adjusted to ps1. From FIG. 4, the sensitivity distribution of
the two sets of microphone arrays has the highest focal point at ps1. The values of the contour
lines are indicated as -5, -10, -15, -20 dB, with the maximum value being 0 dB.
[0008]
The drawback of the conventional sound receiving apparatus shown in FIG. 3 is that the
sensitivity is as high as -10 dB even at points other than the focal point, that is, in the vicinity of
ps5 at which the microphone array is disposed. More generally speaking, there is a problem that
the sensitivity to the point is increased if the microphone is disposed in the vicinity of that point,
even if it is a point other than the focal point.
[0009]
An object of the present invention is to use a plurality of microphones to pick up voice and
music, and to add all the output signals of each microphone in phase, according to the distance
from the focus to each microphone It solves the above-mentioned drawbacks of the delay-andsum array device that gives delay, and receives the sound of focus (S) with high sensitivity over a
wide range of sound field, and greatly suppresses the sound (N) of other places To obtain a high
signal to noise energy ratio.
[0010]
The present invention provides a time delay Di in accordance with the distance ri from the focal
point to each microphone, and a weighting factor for the reciprocal 1 / rik of the power of the
distance ri. It is characterized in that the output sum of each microphone is taken out as
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In the prior art, only the time delay is given according to the distance ri. Therefore, when the
microphone is disposed at a point far from the focal point, there is a drawback that the sensitivity
increases near the microphone position. Therefore, if the reciprocal 1 / rik of the power of
distance ri is given to the microphone output yi as a weighting factor, the microphone at a
position far away from the focal point has a larger value of ri, so the value of the weighting factor
1 / rik is small Become. For this reason, the sensitivity of the microphone far away from the focal
point becomes small, and only the sensitivity of the microphone close to the focal position
becomes high, and a high signal-to-noise energy ratio can be obtained over a wide range of the
sound field.
[0011]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of the present
invention is shown in FIG. 1 with the parts corresponding to those in FIG. In FIG. 1, 16
microphones are attached to two sets of circumferentially-arranged microphone arrays 11 and
12, respectively, and the inverse of the delay value Di and the square value of the distance ri
from each microphone to the focal point (in the case of k = 2) The absolute value of the sum of
the microphone output signal for a sound source placed at an arbitrary position when given as a
weighting factor is given by the following equation.
[0012]
Here, 2i represents the distance from an arbitrary position to the microphone 3i, and ri
represents the distance from the focal point P to the microphone 3i. Fig. 2 shows the sensitivity
distribution 1.1 m below the microphone array by hanging the microphone arrays 11 and 12
shown in Fig. 1 from the ceiling in a room 6.8 m wide, 4.2 m long and 3.1 m high. It represents a
simulation result. Specifically, the magnitude of the output for the sound source placed at each
point was calculated by equation (6) and displayed as a contour line. In the calculation, a free
sound field was assumed, and the average was obtained at an average of 11 points (310 Hz
intervals) of 300 Hz to 3.4 kHz. The two sets of microphone arrays 11, 12 are arranged about
ps2 and ps5, and the focus of the array is adjusted to ps1. From FIG. 2, the sensitivity distribution
of the sound receiving apparatus using two sets of microphone arrays is highest at the focal
point ps1. Further, as in the conventional example of FIG. 4, a good sensitivity distribution can be
obtained over a wide range of a room without any increase in sensitivity at a point far from the
focal point ps1 of the microphone array (near ps5).
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[0013]
In the present invention, the reciprocal 1 / rik of the power of the distance from the focal point
to each microphone 3i is given as the weighting factor. It has been experimentally confirmed that
the value of k at this time may be about 1 ≦ k ≦ 3. The reason is that if k is smaller than 1, the
weighting effect becomes too small, and if k is larger than 3, the weighting effect becomes
excessive, which is equivalent to not using a distant microphone at all. Because it becomes.
[0014]
In FIG. 1, the multiplier 7i is provided at the front stage of the delay unit 4i, but the order may be
reversed.
[0015]
As described above, in the case of using a plurality of microphones in the collection of voice and
music in a reverberant sound field such as a loud speech communication conference, the output
signals of the microphones are all added in the same phase and summed. As in the above, the
time delay is given according to the difference in distance from the focal point to the
microphone, and the reciprocal of the power of the distance from the focal point to each
microphone is multiplied as a weighting factor to take out the respective sums. By collecting the
focus signal with high sensitivity and suppressing the sensitivity to the signal at a point away
from the focus, it is possible to greatly improve the S / N ratio of the focus signal.
[0016]
Brief description of the drawings
[0017]
1 is a block diagram showing an embodiment of a sound receiving device of the present
invention.
[0018]
2 is a diagram showing an example of the sensitivity distribution of the sound receiving device of
FIG.
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[0019]
3 is a block diagram of a conventional sound receiving device.
[0020]
4 is a diagram showing an example of the sensitivity distribution of the sound receiving device of
FIG.
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