Electrical audio signal processing systems and devices – Noise or distortion suppression
Reexamination Certificate
2001-01-10
2004-05-18
Ramakrishnaiah, Melur (Department: 2643)
Electrical audio signal processing systems and devices
Noise or distortion suppression
C381S092000, C381S071120, C379S406100, C379S406120
Reexamination Certificate
active
06738481
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is directed to noise reduction, and more particularly, to an apparatus and method for performing noise reduction for a signal received at a microphone array.
A noise reduction apparatus is typically used in conjunction with hands-free mobile terminals (for example, cellular telephones) and speaker phones, or with speech recognition systems, to reduce noise received at a microphone array of the noise reduction apparatus.
The general structure of different array processing algorithms for noise reduction apparatuses utilizing microphone arrays in conjunction with signal processing can be expressed in the frequency domain as
U
out
(
ω
)
=
∑
i
=
1
N
U
(
ω
,
r
i
)
·
H
*
(
ω
,
r
i
)
where U
out
(&ohgr;) and U(&ohgr;, r
1
) are respectively the Fourier transform of the microphone output and the field u(t, r
i
) observed at the i-th microphone elements with the spatial coordinates r
i
, H(&ohgr;, r
1
) is the frequency response of the filter at the i-th element of the microphone array, and N is the number of microphone array elements.
The determination of the functions H(&ohgr;, r
1
) is the major area of concern in array processing. In conventional array processing, the optimization criteria used for the determination of the functions H(&ohgr;, r
i
) are based on an assumption that the signal field in a limited space, for example an automobile cabin, has a coherent structure. This assumption leads to the following conventional algorithm for the determination of the weighting functions H(&ohgr;, r
1
):
H
(
ω
,
r
i
)
≡
H
0
(
ω
,
r
i
)
=
∑
p
=
1
N
K
N
-
1
(
ω
;
r
i
,
r
p
)
G
(
ω
;
r
p
,
r
0
)
where K
N
−1
(&ohgr;, r
1
, r
p
) denotes the elements of the matrix K
N
−1
(&ohgr;) which is the inverse of the noise spatial correlation function matrix K
N
(&ohgr;) with the elements K
N
(&ohgr;; r
1
, r
p
). G (&ohgr;, r
p
, r
0
) is the Green function which describes the propagation channel between the talker with the spatial coordinates r
0
and the p-th array microphone. However, experimental data and theoretical analysis show that the coherent signal field model is unrealistic for many limited or confined spaces such as automobile environments where wall irregularities will scatter the signal waves propogating inside the automobile cabin.
SUMMARY OF THE INVENTION
A method of reducing noise and a noise reduction apparatus are provided utilizing a microphone array including a plurality of microphone elements for receiving a training signal including a plurality of training signal samples, and a working signal including a plurality of working signal samples. At least one frequency domain convertor is coupled to the plurality of microphone elements for converting the plurality of training signal samples and the plurality of working signal samples to the frequency domain. A signal spatial correlation matrix estimator is coupled to the at least one frequency domain convertor for estimating a signal spatial correlation matrix using the converted plurality of training signal samples, and an inverse noise spatial correlation matrix estimator is coupled to the at least one frequency domain convertor for estimating an inverse noise spatial correlation matrix using the converted plurality of working signal samples. A constrained output generator is coupled to the at least one frequency domain convertor, the signal spatial correlation matrix estimator and the inverse noise spatial correlation matrix estimator for generating a constrained output for the noise reduction apparatus using the converted working signal samples, the estimated signal spatial correlation matrix and the estimated inverse noise spatial correlation matrix.
The noise reduction apparatus may be used in conjunction with or implemented as part of a mobile terminal, a speaker-phone, a speech recognition system, or any other device where noise reduction is desirable.
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patent: 3929481 (1980-03-01), None
Omologo M et al: “Environmental conditions and acoustic transduction in hands-free speech recognition” Speech Communication, Amsterdam, NL, vol. 25, No. 1-3, Aug. 1, 1998, pp. 75-95, XP004148066 ISSN: 0167-6393.
Fischer S et al: “Beamforming microphone arrays for speech acquisition in noisy environments” Speech Communication, Elsevier Science Publishers, Amsterdam, NL, vol. 20, No. 3, Dec. 1, 1996, pp. 215-227, XP004016546 ISSN: 0167-6393.
Le Bouquin R: “Enhancement of noisy speech signals: Application to mobile radio communications” Speech Communication, Elsevier Science Publishers, Amsterdam, NL, vol. 18, No. 1, 1996, pp. 3-19, XP004008920 ISSN: 0167-6393.
Asano F et al: “Speech enhancement using CSS-based array processing” 1997 IEEE International Conference on Acoustics, Speech, and Signal Processing. Speech Processing. Munich, Apr. 21-24, 1997, IEEE International Conference on Acoustics, Speech, and Signal Processing, Los Alamitos, IEEE Comp. Soc. Press, US, vol. 2, Apr. 21, 1997, pp. 1191-1194, XP000822666 ISBN: 0-8186-7920-4.
Khayrallah Ali S.
Krasny Leonid
Coats & Bennett P.L.L.C.
Ericsson Inc.
Ramakrishnaiah Melur
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