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Christiane Antweiler, RWTH Aachen (Germany)
Jörn Grunwald, RWTH Aachen (Germany)
Holger Quack, RWTH Aachen (Germany)
One of the most widely used gradient-based adaptation algorithms is the so called normalized least mean square (NLMS) algorithm. The rate of convergence, misadjustment and noise insensitivity of the NLMS-type algorithm depend on the proper choice of the step size parameter, which controls the weighting applied to each coefficient update. Different step size methods have been proposed to improve the convergence of NLMS-type filters, while preserving the steady-state performance. The step size methods considered here use either a step size parameter which varies with time or a separate, tap-individual step size for each filter tap. The derivation of the respective step size methods is based on different optimization criteria. In this paper a step size parameter is proposed satisfying a combined optimization criterion leading to a time variant and individual step size parameter. The realization aspects of the new concept are discussed for an acoustic echo control application as an example.
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Shoji Makino, NTT Human Interface Labs (Japan)
Klaus Strauss, NTT Human Interface Labs (Japan)
Suehiro Shimauchi, NTT Human Interface Labs (Japan)
Yoichi Haneda, NTT Human Interface Labs (Japan)
Akira Nakagawa, NTT Human Interface Labs (Japan)
This paper proposes a new subband stereo echo canceller that converges to the true echo path impulse response much faster than conventional stereo echo cancellers. Since signals are bandlimited and downsampled in the subband structure, the time interval between the subband signals become longer, so the variation of the crosscorrelation between the stereo input signals becomes large. Consequently, convergence to the true solution is improved. Furthermore, the projection algorithm, or affine projection algorithm, is applied to further speed up the convergence. Computer simulations using stereo signals recorded in a conference room demonstrate that this method significantly improves convergence speed and almost solves the problem of stereo echo cancellation with low computational load.
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Jacob Benesty, Bell Labs (U.S.A.)
Dennis R. Morgan, Bell Labs (U.S.A.)
M. Mohan Sondhi, Bell Labs (U.S.A.)
Teleconferencing systems employ acoustic echo cancelers (AECs) to reduce echos that result from coupling between the loudspeaker and microphone. To enhance the sound realism, two-channel audio is necessary. However, in this case (stereophonic sound) the acoustic echo cancellation problem is more difficult to solve because of the necessity to uniquely identify two acoustic paths. In this paper, we explain these problems in detail and give an interesting solution which is much better than previously known solutions. The basic idea is to introduce a small nonlinearity into each channel that has the effect of reducing the interchannel coherence while not being noticeable for speech due to self masking.
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Valérie Turbin, CNET (France)
André Gilloire, CNET (France)
Pascal Scalart, CNET (France)
We consider an acoustic echo control system composed of a short conventional acoustic echo canceller combined with a post-filter in a teleconference context. The post-filter is implemented in an open-loop structure in the frequency domain, which provides good adaptive performance and flexibility for the choice of the post-filter length. Three post-filtering algorithms are compared in terms of residual echo attenuation and near-end speech distortion. The effect of the post-filter length is also examined. Our study confirms that the post-filtering approach provides high residual echo attenuation. Moreover, it appears that the distortion of the near-end speech can be controlled by choosing appropriately the post-filter length.
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