Patent ID: 7231036

Claim:
An anti-howling circuit for use in an environment having a first transducer for converting a received signal to acoustic output, a second transducer for converting acoustic input to an outgoing signal, and an adaptive echo canceler for generating a predicted echo signal from the received signal by multiplying samples of the received signal by respective tap coefficients, subtracting the predicted echo signal from the outgoing signal to generate a residual signal, and adaptively updating the tap coefficients, comprising: a first envelope detector for detecting a first envelope of the outgoing signal; a second envelope detector for detecting a second envelope of the residual signal; an echo loss calculator for calculating echo attenuation on an echo path from the received signal to the outgoing signal: and a decision circuit for comparing the first envelope with the second envelope, thereby detecting howling, wherein the decision unit detects howling when the second envelope exceeds the first envelope by a threshold ratio that depends on the calculated echo attenuation on the echo path.