US Patent 8355517 Hearing aid circuit with feedback transition adjustment

A feedback transition threshold algorithm assesses and responds to feedback transition events in a hearing aid. The feedback transition threshold algorithm considers short duration trouble indicators, with the preferred primary short duration trouble indicators being the correlation witnessed between the incoming signal in a given frequency band and the same signal delayed by the estimated feedback loop time. If the short duration trouble indicators indicate that feedback squeal is likely and that the external feedback path is changing too quickly for accurate correction by the internal adaptive feedback reduction filter, when the signal level crosses the feedback transition threshold gain is reduced in that frequency band.