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Acoustical echo canceller having an adaptive filter with passage into the frequency domain
| Details |
Inventors: Boudy, Jerome; Capman, Fran.cedilla.ois;
Assignee: Matra Communications (FR)
Primary Examiner: Hunter; Daniel S.
Assistant Examiner: Saint-Surin; Jacques
Attorney, Agent or Firm: Evenson, McKeown, Edwards & Lenahan, P.L.L.C.
The echo canceller comprises an adaptive filter receiving the coefficients of a direct discrete transform into the frequency domain, computed on successive blocks of an input signal and fed via an inverse transform circuit to the subtractive input of an adder for forming an output signal going to the network, and an adaptor circuit for adapting the coefficients of the filter. The adaptor circuit receives the coefficients of successive transforms of blocks of output signal samples via a noise reducer. |
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DETAILED DESCRIPTION It is an object of the invention to provide frequency echo canceller that is improved from the point of view of speed of adaptation, while nevertheless presenting little transmission delay and improving echo cancelling performance.
To this end, the invention uses a spectral subtraction technique, the use of which has already been envisaged in other domains such as speech recognition, taking advantage of the fact that passage into the frequency domain is already available in echo cancellers of the above-defined kind.
Consequently, the invention proposes an acoustical echo canceller suitable for being placed between a hands-free acoustical interface and a communications network, and comprising: an adaptive filter receiving the coefficients of a direct discrete transform in the frequency domain, computed on successive blocks of an input signal, and applied via an inverse transform circuit to the subtractive input of an adder for forming an output signal going towards the network; and an adaptor circuit for adapting the filter coefficients; the echo canceller being characterized in that said adaptor circuit receives the coefficients of the successive transforms of blocks of output signal samples via a noise reducer.
This noise reducer is advantageously a spectral subtracter whose subtractive input receives the coefficients representative of the estimated noise spectral.
It is possible to use various models of noise, depending on the environment.
The model may be estimated a priori, or more generally it may be determined during periods of silence (pauses in the speech of both near and far speakers).
The structure of the noise spectral subtraction means and the algorithms implemented may be those described in the article by Lockwood and Boudy J.
"Experiments with a non-linear spectral subtracter (NSS).
Hidden Markov models and the projection, for robust speech recognition in cars", Speech Communication, Vol.
11, Nos.
2-3, pp.
215-228, June 1992, or in document EP-A-0 534 837
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Telecommunications 
