Analysis The Impact Of Acoustic Factors For Performance Of Adaptive Feedback Cancellation Using In Howling Suppression Algorithm

Ever since sound reinforcement and public address (PA) systems have been in use, their performance has been troubled by the problem of acoustic feedback. Whenever a microphone captures a desired sound signal which is then processed and played back by a loudspeaker in the same environment, as it is the case in a PA system, the loudspeaker signal is unavoidably fed back into the microphone. In this way, a closed signal loop is created which affects the system performance, deteriorating the sound quality and limiting the achievable amplification. Among the different artifacts that are produced by this acoustic coupling between loudspeaker and microphone, the howling effect is without any doubt the most characteristic one.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. Then introduces the three most widely used methods for acoustic feedback control, namely phase-modulating feedback control (PFC), notch-filter-based howling suppression (NHS), and adaptive feedback cancellation (AFC). And give a comparative evaluation of these three methods.For the AFC, theoretically, the better the fit between the estimated and actual feedback path, the larger the achievable maximum stable gain (MSG) increase, if they are the same, the system would no longer exhibit a closed signal loop and hence the MSG would be infinitely large. But in fact the MSG of a system in anechoic room is 17dB. This thesis will explore the reasons causing the difference between theoretical simulation result and actual test result.In addition, the adaptive feedback cancellation has a strong dependence with the model of the acoustic feedback path. Every change in the room will affect the acoustic feedback path and then change the transfer function of the sound field. Because of this series of changes, the performance on system will be affected. This thesis will simulate a series of common surrounding environment changes in the ordinary room, quantitatively analysis the impact of these changes for the actual system.