Abstract: Methods and systems for updating the adaptive filter of an echo canceller. A method of updating the adaptive filter of an echo canceller in which an estimated echo is resolved from a received signal and then subtracted from an incoming echo-contaminated signal so as to produce a filtered output signal, includes: obtaining a corrected impulse response of an echo reconstruction filter (ERF); calculating specified decision measures usable to decide whether to prospectively apply the corrected ERF impulse response or a current ERF impulse response; determining whether application of the corrected ERF impulse response would result in improved echo cancellation; and updating the ERF to apply the corrected impulse response, when it is determined that the updating would result in a lower residual echo.

Abstract: Various methods and systems disclosed compand audio signals using signal prediction, followed by expansion and reconstruction. The methods and systems compress and expand an error signal that represents deviations between samples of the original signal and predicted samples. Each predicted sample is generated by an extrapolation based on a sub-sequence of prior samples of the original signal. A time series of correction samples based on the error signal as it is received from the analog channel after amplitude expansion. Output samples are then generated from the sums of the correction samples and respective predicted samples of a second time series, each of which is extrapolated based on a sub-sequence of prior correction samples. Numerous variations are also disclosed.

Abstract: An improved audio mixing system that does not instantaneously switch a microphone from the attenuated level to the unattenuated level in response to level changes on the microphone is disclosed. The system is not limited to one type of microphone and does not depend on separate sensing microphones to determine the background noise level. In addition, the active signal is not amplitude modulated by extraneous noise inputted through inactive microphones.

Abstract: A sound system microphone equalization apparatus and method comprising a plurality of filters programmable by a microprocessor. User interfaces permit adjustment for each microphone channel of the parameters of the three notch filters, and four tone control filters in the filter network.

Abstract: A multichannel sound system comprising a plurality of microphones and loudspeakers. Rate controlled, variable attenuation of the audio signal is provided as a function of loudspeaker and microphone proximity. The use of optical isolators or analog switches with RC delay circuits to control the rate of attenuation eliminates objectionable switching transients. Selective attenuation of loudspeakers in proximity to active microphones eliminates audio feedback.