Abstract: A microphone detects acoustic waves from speakers, or for a two-way voice communication device, a user's voice and background noise, and produces a corresponding signal; a subtractor finds the difference between the microphone signal and a desired audio signal; a transform process produces over a time period a signal corresponding to the amplitude of each frequency component of the difference signal; from the transform process a bandpass filter passes only frequency components within selected bands; a speech interference noise level calculator calculates a combination of the amplitudes of the bandpass filtered frequency components; and a solver uses the combination to produce, according to an algorithm, a signal for controlling the gain of an audio amplifier. Phase and amplitude correlation can be done prior to subtraction.

Abstract: A microphone detects acoustic waves from speakers and background noise, and produces a corresponding signal that is digitized; also digitized is a desired audio signal; the two digitized signals are phase and amplitude correlated; a subtractor finds the difference between the correlated microphone and audio signals; a transform process produces over a time period a signal corresponding to the amplitude of each frequency component of the difference signal; from the transform process a bandpass filter passes only frequency components within selected bands; a speech interference noise level calculator calculates a combination of the amplitudes of the bandpass filtered frequency components; and a solver uses the combination to produce, according to an algorithm, a signal for controlling the gain of an audio amplifier.