in a system in which echo transferred from a received signal to an outgoing signal is canceled by subtracting an adaptively predicted echo signal from the outgoing signal , howling is detected by detecting the effect of the predicted echo signal . the detected effect preferably depends on the magnitude or polarity of the predicted echo signal . the effect may be detected by comparing an envelope of the received signal or outgoing signal with a corresponding envelope of the residual outgoing signal left after echo cancellation . the echo attenuation on the echo path from the received signal to the outgoing signal may also be calculated , the conditions for howling detection being made more stringent as the detected echo attenuation increases . when howling is detected , it may be suppressed by attenuating the residual outgoing signal or initializing an adaptive filter that generates the predicted echo signal .