Method for cancelling multi-channel acoustic echo and multi-channel acoustic echo canceller

An echo canceller with N sound signal channels each having a loudspeaker and an associated microphone, N being an integer greater than or equal to 1, including:

• means for computing auxiliary signals, comprising:
• means for forming blocks each containing a pre-specified number of samples of the sound signal, two successive blocks mutually overlapping over a pre-specified number of samples;
• means for weighting the samples of each block by an apodisation window, placed at the output of the means for forming blocks;
• means for computing a Fourier transform, placed at the output of the weighting means;
• means for computing the lower and upper frequency values of adjacent critical bands, or a look-up table containing these values;
• means for computing an energy distribution function on the critical bands, the value, in a given critical band, of the energy distribution function being computed by adding the energy of the different spectrum lines belonging to this critical band;
• a second look-up table, containing values representing the basilar spreading functions each associated with a given critical band;
• means for computing a spread spectrum Ei, by computing, for a given critical band, the convolution product of the energy distribution function and the spreading function associated with this critical band;
• means for computing a correction factor Oi associated with a given critical band;
• means for computing a frequency masking threshold Ti associated with a given critical band, from the spread spectrum and from the correction factor Oi associated with this critical band, the frequency masking threshold Ti being defined as follows:
• 10 log10Ti=10 log10Ei−Oi−Ci
• where Ci is an additional threshold correction parameter;
• means for generating synthetic signals having the spectral characteristics of a white noise;
• control means, connected to the N sound signal channels, for computing for each critical band said additional threshold correction parameter Ci from several characteristics of the sound signals from the N channels;
• means for bringing the level of a synthetic signal to the value of the associated frequency masking threshold, so as to obtain an auxiliary signal;
• means for computing an inverse Fourier transform;
• memory means for storing the result of the processing of the successive blocks;
• means for combining the result of the processing of a block with the result of the processing of the previous block;
• sequential reading means connected to said memory means, in order to pass the rate of data from the block rate to the sample rate;
• N first adder means respectively placed on the N sound signal channels, for adding on each channel the received sound signal and the associated auxiliary signal;
• N×N adaptive filtering means, including N adaptive filtering means associated with each of the N microphone channels, and each having coefficients which form an estimation of the impulse response of the acoustic coupling path between the loudspeaker and the microphone associated with one of the N sound signal channels;
• second adder means, connected to the output of the N adaptive filtering means associated with each microphone channel, for adding the output signals of these N adaptive filtering means;
• N subtractor means each placed at the output of said second adder means and connected respectively to the microphones of the N sound signal channels, for subtracting on each microphone channel the signal obtained at output from said second adder means from the signal received by the microphone of this channel;
• means for computing on each microphone channel an estimation error from the result supplied by the subtractor means connected to the microphone of this channel;
• means for correcting in an iterative manner the respective coefficients of the N adaptive filtering means associated with each of the N microphone channels, as a function of the estimation error associated with each microphone channel.