Patent ID: 6868162

Claim:
An apparatus for controlling a gain of an audio signal broadcast by a loudspeaker into a room having ambient noise, comprising: a first input for receiving the audio signal; a second input for receiving an ambient room signal detected by a microphone, the ambient room signal having a noise portion representing the ambient noise and an audio portion representing the audio signal; an adaptive filter for adaptively filtering the audio signal to generate a filtered signal that approximates the audio portion of the ambient room signal, the adaptive filter having a plurality of adaptation coefficients that are modified according to a predetermined formula having a threshold for limiting the rate of variation of the adaptation coefficients; an error signal generator for subtracting the filtered signal from the ambient room signal to generate an error signal; a compander for adjusting the rain of the audio signal responsive of the error signal to compensate for the ambient noise; a down-sampler for sampling the audio signal at a sample rate lower than the highest frequency component of the audio signal, thereby Generating a down-sampled audio signal, and wherein said adaptive filter adaptively filters the down-sampled audio signal to generate the filtered signal; and wherein the adaptation coefficients are updated according to the formula Wi ⁡ ( n + 1 ) = Wi ⁡ ( n ) + min ⁡ [ beta , e ⁡ ( n ) ] * u ⁡ ( n - i ) epsilon * E ⁡ ( n ) , where W i (n) is representative of the i-th adaptation coefficient for the n-th audio sample, e(n) is representative of the error signal, u(n−i) is representative of the (n−i)th sample of the down-sampled audio signal, E(n) is representative of the energy level of the audio signal, beta is the threshold value, and epsilon is a stability coefficient.