Study On Acoustic Feedback Suppression Algorithm

The acoustic feedback problem is a long-standing problem appearing in sound reinforcement systems and public address systems. It will seriously affect the clarity of the sound, and even to produce self-excited whistle, while the more serious of the whistle may cause the tweeter of the amplifier and the speaker in the system burned. Therefore, the acoustic feedback suppression is an important topic in sound amplifying system. Despite decades of research on automatic acoustic feedback control, many PA system technicians still prefer to prosecute manual control of acoustic feedback. It can be seen that effectiveness and reliability are the emphasis of the study of acoustic feedback control algorithm.The main strength of AGC methods is their reliability:if the gain is sufficient-ly reduced, an unstable system is guaranteed to be stabilized. In NHS, the gain is reduced in narrow frequency bands around critical frequencies which is robust. The AFC method is superior to the PFC and NHS methods in terms of achievable amplifi-cation and sound quality, which sometimes lacks robustness. The paper apply a NHS method in which the howling detection is based on a frequency analysis of the AFC feedback path estimate, and combine AGC as a "rescue"The main contributions of this work are summarized as follows:1. we introduce the feedback problem and provide an overview of the state of the art in acoustic feedback control, by reviewing relevant scientific papers and patents that have been published over the past decades.2. The acoustic feedback problem is formulated in a formal way,where the key result is the Nyquist stability criterion, based on which all the acoustic feedback control methods can be derived. 3. We used the AEQ method based on zero-crossing rate to control acoustic feed-back.4. The NHS method is in more detail.5. A hybrid algorithm which combines AFC, NHS and AGC method has been proposed.6.These methods are then evaluated in terms of the resulting sound quality, the achievable amplification, as well as their reliability.