Method of adaptively adjusting the coefficients of a digital fil

Details Method of adaptively adjusting the coefficients of a digital fil Method of adaptively adjusting the coefficients of a digital fil

1997-11-13

2000-03-21

Hoff, Marc S.

Data processing: measuring, calibrating, or testing

Measurement system

Measured signal processing

702193, 702194, 702195, 370286, H04B 320

Patent

active

060412909

ABSTRACT:
Digital filters are used to compensate for echoes in a transmission system in which unwanted couplings occur between a signal value in the receiving direction and a signal value in the transmitting direction. The correct adjustment of the filter coefficients has a considerable influence on the achievable echo compensation. Disturbance signals such as background noises, nonlinear effects in A/D converters or an active local speaker can briefly change the adjustment of the filter coefficients in a way so that the digital filter does not compensate for the echoes and causes additional echoes in unfavorable cases. In accordance with the invention a set of filter coefficients (C(j)) are weighted with an envelope curve (H(j)) and an error measurement (F(j)) is determined therefrom. Depending on the magnitude of the error measurement (F(j)), the filter coefficients (ci) are used for further processing or are discarded. The pertinent arrangement comprises a first digital filter (1) for which the filter coefficients (ci) are continuously calculated in accordance with the NLMS algorithm. These filter coefficients (ci) are stored, weighted and the best values are used to adjust a second digital filter (7) whose output signal (9) is subtracted from the echo-affected signal, creating an echo-free output signal (10) and thus significantly increasing the quality of a natural and undisturbed transmission, even with short-time disturbances.

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Hun, Tilman, et al, Kombination von Gerauschreduktion und Echokompensation beim Freisprechen, In: Nachrichtentech, Elektron, Berlin 43, 1993, H. 6, pp. 274-280, (German).
JP 07066758 A, Patent Abstracts of Japan, (abstract xlation only).
JP 07074681 A, Patent Abstracts of Japan, (abstract xlation only).
"The Telecommunications Engineer", Science and Life Publishers, Georg Heidecker GmbH Erlangen, 48th year, Oct. 1994, pp. 27-29, (German).

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