Acoustic feedback can be well demonstrated by the public address system, as illustrated in the following diagram. When the microphone and speakers are positioned in close distance and oriented in a certain direction, howling may occur. In those situations people usually make howling disappear by varying the microphone orientation. However a more reliable solution is to employ acoustic digital feedback cancellation. VOCAL technologies has developed acoustic digital feedback cancellation solutions for various applications. Howling can also occur in hearing aids, ear-buds, in-car communication systems whenever the acoustic signal path forms a loop between the microphone and speaker. The closed loop makes it possible for the speaker audio output to reinforce the microphone input sound for certain frequencies. Howling usually manifests as sharp peaks of equal distance in spectrum analysis, and the build-up rate is frame-by-frame exponential. These unique features distinguish feedback problems from echo problems. Built upon our matured technologies for acoustic echo cancellation, VOCAL provides solutions specifically designed for acoustic feedback applications. The optimizations are implemented in VOCAL acoustic feedback cancellation library module.