Electrical audio signal processing systems and devices – Directive circuits for microphones
Reexamination Certificate
2000-07-26
2003-07-29
Mei, Xu (Department: 2644)
Electrical audio signal processing systems and devices
Directive circuits for microphones
C381S122000
Reexamination Certificate
active
06600824
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microphone array system. In particular, the present invention relates to a system including two microphones arranged on one coordinate axis that estimates a sound to be received in an arbitrary position on that dimensional axis by performing received sound signal processing and thus can estimate sounds in numerous positions with a small number of microphones.
2. Description of the Related Art
Hereinafter, a sound-estimation processing technique utilizing a conventional microphone array system will be described.
A microphone array system includes a plurality of microphones, and performs signal processing by utilizing sound signals received at each microphone. The objectives, the structures, the use and the effects of the microphone array system are varied significantly by how microphones are arranged in the sound field, what kind of sounds are received, and what kind of signal processing is performed. In the case where there are a plurality of sound sources of desired sounds and noise in the sound field, enhancing the desired sounds and suppressing noise with high quality are main tasks to be achieved by received sound processing with microphones. Detection of the positions of the sound sources is useful for various applications such as teleconference systems, guest-reception systems or the like. In order to realize processing for enhancing a desired sound, suppressing noise and detecting the position of a sound source, it is useful to use the microphone array system.
In the conventional technique, in order to improve quality in enhancing a desired sound, suppressing noise and detecting the position of the sound source, signal processing is performed with an increased number of microphones constituting the array in order to obtain more data of received sound signals.
FIG. 17
shows a microphone array system used for desired sound enhancement processing by conventional synchronous addition. In the microphone array system shown in
FIG. 17
, reference numeral
171
denotes real microphones MIC
0
to MIC
n−1
constituting a microphone array, reference numeral
172
denotes delay units D
0
to D
n−1
for adjusting timing of the signals of the sounds received by the microphones
171
, and reference numeral
173
denotes an adder for adding the signals of the sounds received by the microphones
171
. In the desired sound enhancement by the conventional technique, a sound from a specific direction is enhanced by adding the numerous components wherein the received sound signals which become components for the addition processing are delayed for synchronization. In other words, sound signals used for the synchronous addition signal processing are increased in number by increasing the number of the real microphones
171
. Thus, the intensity of the desired sound is increased. In this manner, the desired sound is enhanced so that a distinct sound is picked out. In noise suppression processing, noise is suppressed by performing synchronous subtraction. In processing for detecting the position of a sound source, synchronous addition or calculation of cross-correlation coefficients is performed with respect to an assumed direction. Thus, in these cases as well, sound signal processing is improved by increasing the number of microphones.
However, this technique for microphone array signal processing that can be improved by increasing the number of microphones is disadvantageous in that a large number of microphones are required to be prepared to realize high quality sound signal processing, and therefore the microphone array system results in a large scale. Moreover, in some cases, it may be difficult to physically arrange a necessary number of microphones for sound signal estimation with required quality in a necessary position.
In order to solve the above problems, it is desired to estimate a sound signal that would be received in an assumed position based on actual sound signals received by actually arranged microphones, instead of receiving a sound by a microphone that is arranged actually. Furthermore, using the estimated signals, enhancement of a desired sound, noise suppression and detection of a sound source position can be performed.
The microphone array system is useful in that it can estimate a sound signal to be received in an arbitrary position on an array arrangement, using a small number of microphones. The microphone array system estimates a sound signal to be received in an assumed position on the extension line (one-dimension) of a straight line on which a small number of microphones are arranged. Although actual sounds propagate in a three-dimensional space, if a sound signal to be received in an arbitrary position on one axis direction can be estimated, a sound signal to be received in an arbitrary position in a space can be obtained by estimating and synthesizing sound signals to be received in the coordinate positions on the three axes in the space, based on the estimated sound signal to be received in the position on each axis. The microphone array system is required to estimate a signal from a sound source with reduced estimation errors and high quality.
Furthermore, it is desired to develop an improved signal processing technique for signal processing procedures used for the sound signal estimation so as to improve the quality of the enhancement of a desired sound, the noise suppression, the sound source position detection.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a first microphone array system that can estimate a signal to be received in an arbitrary position on an axis by arranging two microphones on the axis.
It is another object of the present invention to provide a second microphone array system that can estimate a signal to be received in an arbitrary position on a plane by arranging three microphones on the plane.
It is another object of the present invention to provide a third microphone array system that can estimate a signal to be received in an arbitrary position in a space by arranging four microphones in the space in such a manner that they are not on the same plane.
In order to achieve the above objects, the first microphone array system of the present invention includes two microphones and a sound signal estimation processing part, and estimates a sound signal to be received in an arbitrary position on a straight line on which the two microphones are arranged. The sound signal estimation processing part expresses a sound signal estimated to be received in a position on the straight line on which the two microphones are arranged by a wave equation Equation 5, assuming that the sound wave coming from a sound source to the two microphones is a plane wave. The sound signal estimation processing part estimates a coefficient b cos &thgr; of the wave equation Equation 5 that depends on the direction from which the sound wave comes, assuming that the average power of the sound wave that reaches each of the two microphones is equal to that of the other microphone. The sound signal estimation processing part estimates a sound signal to be received in an arbitrary position on the same axis on which the microphones are arranged, based on the sound signals received by the two microphones.
P
(
x
i
+
1
,
y
0
,
t
j
)
-
P
(
x
i
,
y
0
,
t
j
)
=
a
{
v
x
(
x
i
,
y
0
,
t
j
+
1
)
-
v
x
(
x
i
,
y
0
,
t
j
)
}
{
v
x
(
x
i
+
1
,
y
0
,
t
j
)
-
v
x
(
x
i
,
y
0
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t
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)
}
=
b
cos
θ
{
p
(
x
i
+
1
,
y
0
,
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)
-
p
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x
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+
1
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y
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-
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)
}
Equation
5
where x and y are respective spatial axes, t is a time, v is an air particle velocity, p is a sound pressure, a and b are coefficients, and &thgr; is the direction of a sound source.
By the above embodiment, a sound signal to be received in an arbitrary position on the same ax
Armstrong Westerman & Hattori, LLP
Fujitsu Limited
Mei Xu
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