An exact analysis of the critically subsampled two-band modelization scheme is given, and it is demonstrated that adaptive cross-filters between the subbands are necessary for modelization with small output errors. It is shown that perfect reconstruction filter banks can yield exact modelization. These results are extended to the critically subsampled multiband schemes, and important computational savings are seen to be achieved by using good quality filter banks. The problem of adaptive identification in critically subsampled subbands is considered and an appropriate adaptation algorithm is derived. The authors give a detailed analysis of the computational complexity of all the discussed schemes, and experimentally verify the theoretical results that are obtained. The adaptive behavior of the subband schemes that were tested is discussed. >

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Adaptive filtering in subbands with critical sampling: analysis, experiments, and application to acoustic echo cancellation

Adaptive filtering in subbands is a new technique for the real-time identification of large impulse responses like the ones encountered in acoustic echo cancellation. This tech- nique generally allows computational savings as well as better convergence behavior. We give first an exact analysis of the critically subsampled two band modelization scheme. We demonstrate that adaptive cross-filters between the subbands are necessary for modeliza- tion with small output errors; moreover, we show that perfect reconstruction filter banks can yield exact modelization. We ex- tend those results to the critically subsampled multiband schemes, and we show that important computational savings can be achieved by using good quality filter banks. Then we consider the problem of adaptive identification in critically sub- sampled subbands, and we derive an appropriate adaptation algorithm. We give a detailed analysis of the computational complexity of all the discussed schemes, and we verify experi- mentally the theoretical results that we have obtained. Finally, we discuss the adaptive behavior of the subband schemes that we have tested. We generally observe some degradation of the convergence performance in comparison with conventional schemes; however, the overall performance could be acceptable in practical use.

Adaptive Filtering in Subbands with Critical Sampling: Analysis, Experiments, and Application to Acoustic

Subband adaptive filtering has attracted much attention lately. In this paper, we propose a new structure and a new formulation for adapting the filter coefficients. This structure is based on polyphase decomposition of the filter to be adapted and is independent of the type of filter banks used in the subband decomposition. The new formulation yields improved convergence rate when the LMS algorithm is used for coefficient adaptation. As we increase the number of bands in the filter, the convergence rate increases and approaches the rate that can be obtained with a flat input spectrum. The computational complexity of the proposed scheme is nearly the same as that of the fullband approach. Simulation results are included to demonstrate the efficacy of the new approach.

A new approach to subband adaptive filtering

The hands-free telephone problem: an annotated bibliography

An acoustic echo canceller based on signal decorrelation and subband techniques is developed. A decorrelation algorithm is combined with a variable loop gain method. Echo cancellation characteristics superior to those of the conventional normalized least-mean-square (NLMS) adaptation algorithm are obtained through computer simulation. The implementation of an acoustic subband echo canceller with high speech quality is demonstrated. Experiments confirm echo cancellation in excess of 40 dB over the 7 kHz frequency band using hardware with a total of 4000 tap finite impulse response (FIR) filters. The decorrelation algorithm increases convergence speeds for colored signals by about three times, and for speech signals by more than two times over those of the NLMS algorithm. >

An acoustic echo canceller using subband sampling and decorrelation methods

A structure for the subband acoustic echo canceler is proposed that avoids filter banks in the sending line and the consequent delay. In this arrangement of the filter banks, the conventional least-mean-square algorithm is modified and an additional adaptive filter is included. Simulation results are given, and a real application is reported. >

A new structure for sub-band acoustic echo canceler

The design of a zero delay subband acoustic echo canceller (AEC) is presented. The filter banks are realized by a simplified weighted overlap-add method and oversampling is used to avoid aliasing problems. Complex adaptive filters are used within the filter banks. The design considerations and hardware implementation are discussed in some detail. Parallel processing, pipeline techniques, short machine cycle time and dedicated buses are applied in the hardware implementation to realize a 2048-tap AEC in a single custom chip with existing technology. Simulation results are given and its advantages are shown to be sufficient echo return loss, echo removal in the whole frequency range, and computational saving. >

H. Bes

Papers

A new structure for sub-band acoustic echo canceler

Design of a zero delay subband acoustic echo canceller

No-delay subband acoustic echo canceller