Ericsson Gmbh

Jim Agne Rasmusson

Paul W Dent

Eric Douglas Romesburg

Ronald J Johnsen

Methods and apparatus for achieving echo suppression in communications systems include an echo suppressor, referred to herein as an AC-center attenuator, which attenuates the echo component of a communications signal by multiplying a portion of the communications signal by an appropriate scale factor. Specifically, the AC-center attenuator scales that portion of the communications signal lying within a sliding attenuation window. The attenuation window tracks the communications signal so that the AC-center attenuator suppresses the echo component while passing other signal components of interest (e.g., near-end speech and noise). The scale factor within the attenuation window, and the size of the attenuation window itself, are dynamically adjusted so that the AC-center attenuator introduces minimum signal distortion and few audible artifacts. The dynamic adjustment is carried out to provide a desired round-trip echo gain in a system in which the AC-center attenuator is implemented. Toward that end, a measure of the echo attenuation achieved by an echo suppressor (e.g., an adaptive echo canceler) is obtained by computing a ratio of first and second values, wherein the first and second values indicate energy levels in the echo suppressor output and input signals, respectively. Alternately, the echo attenuation achieved by a blockwise-updating echo canceler is obtained by computing a ratio of first and second values, wherein the first value indicates a level of energy in a set of update coefficients of the echo canceler and the second value indicates a level of energy in the echo canceler input signal. In each case, the computed ratio can be used to adjust the level of attenuation provided by a residual echo suppressor.

Methods and apparatus for improved echo suppression in communications

A measure of a degree of convergence in an adaptive filter arrangement is derived from the comparison of an amount of adaptation occurring in the adaptive filter arrangement, over a predetermined period of time, with a normalizing value accumulated for the same period. Supplemental signal processing may be invoked, modified or withdrawn based upon the degree of convergence indicated.

Gauging convergence of adaptive filters

An extended coefficient resolution range is provided in an adaptive filter arrangement by utilizing several filters, in combination, to represent the extended resolution range. The coefficients of a first filter represents a high portion of the extended range, while the coefficients of the second filter represent low portions of the extended range. The two filters operate in parallel to filter an input signal, and the outputs of the filters are combined to produce the filtered signal. A low portion of the coefficients of the first filter overlap an upper portion of the coefficients of the second filter. The coefficients of the first filter are periodically updated from the overlapping portions of the coefficients of the second filter, after which the overlapping portions of the coefficients of the second filter are reset. In accordance with another aspect of the invention, the amount of overlap may be adjusted to dynamically change the resolution range of the filter. The coefficients of the first and second filters are capable of variably overlapping to expand or contract the resolution range in response to changes in the system being monitored. The degree of overlap can also be adjusted to provide an appropriate resolution range corresponding to when the system is stable. An adaptive process is used to update filter coefficients.

Resolution enhancement of fixed point digital filters

In an audio system, a loudspeaker responds to an input signal producing a sound pressure wave having a linear component, which is linear function of the input signal, and an undesired non-linear component, which is a non-linear function of the input signal. Accordingly, it is desirable to reduce the non-linear component of the output sound pressure wave. An adaptive precompensating audio system for reducing this non-linear component includes a loudspeaker for producing a sound pressure wave and a precompensating filter for precompensating an input signal representative of the desired sound pressure wave. In addition, a microphone may be used to convert the resulting sound pressure wave into a sound signal and a precompensating filter modifier may be used to modify the precompensating filter in response to the sound signal. Preferably, the precompensating filter transforms the input signal using an inverse of an estimated transfer function for the loudspeaker.

Apparatus and method for adaptively precompensating for loudspeaker

An echo-canceling system and method uses an echo estimate to modify the error signal which is obtained by the difference between an echo signal and the echo estimate. The modified error signal, rather than the error signal itself, is transmitted. By using the echo estimate as a parameter for modifying the error signal, improved hands-free performance may be obtained in a vehicular radiotelephone, such as a cellular telephone. Preferably, modification of the electrical error signal is performed by a center clipper which removes a portion of the electrical error signal which is below a variable threshold, wherein the variable threshold is determined by the echo estimate electrical signal. The variable threshold may be produced from the echo estimate electrical signal using an envelope detector.

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Brosarp, Sweden

Jim Agne Rasmusson