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JP2004112701

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DESCRIPTION JP2004112701
An object of the present invention is to provide a method of correcting a microphone reception
signal in a microphone array capable of converting a reception signal of each microphone
constituting a microphone array into a signal having no difference in delay time. A method of
correcting a microphone reception signal in a microphone array having three or more
microphones mounted on a portable device and arranged at equal distances from an origin on an
xy plane of a three-dimensional space based on the portable device. When the microphone array
coordinate system is rotated around the x axis and around the y axis such that the difference in
delay time when the target sound source signal reaches each microphone is zero, the rotation
angle around the x axis and the rotation angle around the x axis calculating rotation angles about
the y-axis at predetermined time intervals, and converting the received signals of the respective
microphones into signals having no delay time difference based on the calculated rotation angles
about the x-axis and the y-axis. Is equipped. [Selected figure] Figure 2
Sequential correction method for microphone array coordinate system, correction method and
correction device for microphone reception signal in microphone array
[0001] The present invention relates to a method of sequentially correcting a microphone array
coordinate system, a method of correcting a microphone reception signal in a microphone array,
and a correction apparatus. In recent years, research on noise removal using a microphone array
has been actively conducted as one of the approaches for realizing remote speech recognition. In
addition, in portable voice recognition devices that are drawing attention, it is necessary to use
close-talking microphones at present to ensure the performance of voice recognition, but in the
future microphone arrays in PDA (Portable Digital Assistance) etc. The use of However, the use of
a microphone array in a mobile device requires the beam pattern to be designed adaptively even
if the sound source direction is fixed because the spatial position of each microphone element
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changes momentarily. is there. SUMMARY OF THE INVENTION The present invention provides a
method of sequentially correcting a microphone array coordinate system which can keep a sound
source direction to a microphone array constant and can use fixed beamforming. The purpose is
Another object of the present invention is to provide a method and circuit for correcting
microphone reception signals in a microphone array that can convert the reception signals of the
microphones constituting the microphone array into signals having no delay time difference with
each other. . According to the first aspect of the present invention, there is provided a method of
sequentially correcting a coordinate system of a microphone array mounted on a portable device,
wherein a sound source direction with respect to the microphone array is kept constant. As a
result, the microphone array coordinate system is corrected sequentially. The invention
according to claim 2 is a microphone array having three or more microphones mounted on a
portable device and arranged at equal distances from the origin on the xy plane of a threedimensional space based on the portable device. In the microphone reception signal correction
method in, the microphone array coordinate system is rotated around the x axis and the y axis so
that the difference in delay time when the target sound source signal reaches each microphone is
zero. Calculating the rotation angle around the x axis and the rotation angle around the y axis at
predetermined time intervals, and delaying the received signal of each microphone based on the
calculated rotation angle around the x axis and rotation angle around the y axis It is
characterized in that it comprises the step of converting into a signal without time difference.
The invention according to claim 3 is a microphone array having three or more microphones
mounted on a portable device and arranged at equal distances from the origin on the xy plane of
a three-dimensional space based on the portable device. In the microphone reception signal
correction device in, the microphone array coordinate system is rotated around the x axis and the
y axis so that the difference in delay time when the target sound source signal reaches each
microphone becomes zero. , And means for calculating the rotation angle around the x axis and
the rotation angle around the y axis at predetermined time intervals, and delaying the received
signal of each microphone based on the calculated rotation angle around the x axis and rotation
angle around the y axis It is characterized in that it comprises means for converting it into a
signal without time difference. BEST MODE FOR CARRYING OUT THE INVENTION Embodiments
of the present invention will be described below with reference to the drawings. [1] Definition of
Microphone Array Coordinate System FIG. 1 shows a microphone array coordinate system. The
microphone array is mounted on a portable device. The microphones M1, M2 and M3 are
arranged on the xy plane of a three-dimensional space (three-dimensional coordinate system)
with a portable device as a reference, at the vertex of an equilateral triangle having a length of 2d
with one side centered on the origin o It is done. The coordinates pi of the microphone Mi (i = 1,
2, 3) are expressed by the following equations (1), (2) and (3) from the geometrical relationship.
In the case of rotating the coordinate system about the x and y axes, the rotation angles θx and
θy are the rotation axes. Seeing the origin o from the positive direction side of the coordinate
axis, and defining that the rotation angle takes a positive value when the coordinates are turned
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counterclockwise. At this time, rotation matrices Tx (θx) and Ty (θy) related to rotation around
the x and y axes are given by the following equations (4) and (5). Therefore, assuming that the
rotation angles at time j are θx and θy, the coordinates pi of the microphone Mi <(j)> Is given
by the following equation (6). [Img class = EMIRef id = 197964177-00005 ] /> [2]
Description of Circuit for Correcting Microphone Reception Signal in Microphone Array FIG. Fig.
6 shows a circuit for correcting microphone reception signals in a microphone array.
Received signals x 1 (t), x 2 (t) and x 3 (t) of the microphones M 1, M 2 and M 3 are sent to the
correction circuit 10. The correction circuit 10 receives the reception signals x1 (t), x2 (t), x3 (t)
so that the difference between the delay times of the reception signals x1 (t), x2 (t), x3 (t) is zero.
The signal is corrected and output as signals y1 (t), y2 (t) and y3 (t). Hereinafter, the correction
method by the correction circuit 10 will be described. In this embodiment, it is assumed for the
sake of simplicity that all the signals come in plane waves. Assuming that the target sound source
signal is s (t) and the delay time when it arrives at the microphone Mi is δi, the sound reception
signal xi (t) at the microphone Mi is generally expressed by the following equation (7) . <Img
class = "EMIRef" id = "197964177-000006" /> where ni (t) is a noise signal at the microphone
Mi. Here, it is assumed that the microphone array coordinate system is rotated by rotation angles
θx and θy such that the target sound source direction with respect to the microphone array is
on the z axis, that is, the delay time difference between the microphones becomes zero. At this
time, the delay time δi can be expressed by the following equation (8) using the rotation angles
θx and θy. <Img class = "EMIRef" id = "197964177-000007" /> where c is the velocity of
sound. The output signal yi (t) corrected using this delay time δi (θx, θy) can be expressed as
the following equation (9). Where img is given by sinc (x) = sin (πx) / πx, and T is a sampling
interval. Here, a square error e such as the following equation (10) is used. This is an evaluation
function that takes a minimum value when the delay time difference between the output signals
yi becomes 0. <img class = "EMIRef" id = "197964177-00009" It is.
When the steepest descent method is used to estimate the rotation angles θx and θy which
minimize the square error e, the rotation angles θx <(k + 1)> and θy <(k + 1)> estimated at the k
+ 1 time are estimated at the k time The rotational angles θx <(k)> and θy <(k)> are calculated
as in the following equations (11) and (12). <Img class = "EMIRef" id = "197964177-000010" />
where μ is a step size parameter. That is, the correction circuit 10 calculates and obtains the
rotation angles θx and θy such that the delay time difference between the output signals yi
calculated previously is 0 based on the above equations (11) and (12). An output signal yi is
calculated on the basis of the rotational angles .theta.x, .theta.y and the equation (10). It should
be noted that calculating the rotation angles θx and θy such that the delay time difference
between the output signals yi previously calculated is 0 means, in other words, to keep the sound
source direction relative to the microphone array constant. It corresponds to correcting the array
coordinate system. [3] Evaluation In order to confirm the effectiveness of the method of the
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present invention, evaluation was performed by computer simulation. [3.1] Simulation Conditions
The target sound source signal used was shaped gaussian noise with an average of 0 and a
variance of 0.05. The noise signal is zero. The microphone distance 2d is 0.1 m, and the sampling
frequency is 48 kHz. The sound reception signal xi (t) at the microphone Mi is simulated by the
target sound source signal shifted by +3, −5 and +2 samples and −4, +3 and +1 samples.
However, one sample is a sampling interval T. Further, the step size parameter μ of the
equations (11) and (12) in the estimation of the rotational angles θx and θy is 0.01, and the
initial value of the rotational angle θx <(0)>, θy <(0)> Is 0 rad. [3.2] Simulation Result The
simulation result is shown in FIG. The horizontal axis is the number of updates k, and the vertical
axis is the estimated rotation angles θx and θy. The solid line shows the result for the sound
receiving signal xi (t) simulated by shifting the target sound source signal by +3, -5 and +2
samples, and the broken line shows the received sound simulating the target sound source signal
shifted by -4, +3 and +1 samples The results for the signal xi (t) are shown.
It can be confirmed that the estimated values of the rotation angle converge to theoretical values
(θx, θy) = (0.30, 0.59) and (0.14, -0.51), respectively. [4] Summary In the portable microphone
array assumed to be used in mobile devices, a method is proposed to sequentially correct the
microphone array coordinate system so that the sound source direction to the microphone array
is maintained constant. Computer simulation confirmed that the correction was possible.
According to the present invention, the sound source direction to the microphone array can be
kept constant, and the use of fixed beam forming becomes possible. According to the present
invention, the reception signals of the microphones constituting the microphone array can be
converted into signals having no difference in delay time. BRIEF DESCRIPTION OF THE
DRAWINGS FIG. 1 is a schematic view showing a microphone array coordinate system. FIG. 2 is a
block diagram showing a configuration of a circuit for correcting a microphone reception signal
in a microphone array. FIG. 3 is a graph showing simulation results. [Explanation of the code]
M1, M2, M3: Microphone
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