Adaptive Acoustic Feedback Suppression Algorithm

Acoustic feedback is a common phenomenon in public addressing systems. Howling, which results from the feedback, restrains the gain increasing and obscures clarity. When feedback goes serious, the public addressing systems even cannot work. Traditional feedback exterminating means include improving rooms'acoustic property, cascading equalizers or frequency-shifters in the sound amplifying link, etc. Nevertheless, these means are inconvenient to operate and cause unnecessary decrease of gain and sound fidelity.Fortunately, great developments in digital signal processing technology over the last decades provide advanced solutions: automatic feedback suppression. It overcomes shortcomings of traditional means, does little harm to desired sounds, improves the gain prominently and is easier to be operated. However, most of automatic feedback suppressors in domestic market are imported from oversea and expensive. We must develop automatic feedback suppressor with own intellectual property to possess enormous competitive strength of marketing.According to these background,we have proposed 3 auto acoustic feedback suppressor schems:Scheme I.Two major algorithms - the wavelets or filter banks theories and the frequency sample filter theory have been implemented to make up the scheme a adaptive acoustic feedback suppressor.Scheme II.A scheme based on acoustic system recongniton and adaptive filter.Compared with the traditional adaptive feedback suppressor, this system has been added a new component, the residual echo suppressor component.Scheme III. A system combining FFT algorithm with Chirp-z Transform to detect feedback rapidly and accurately. Then, adopting a filter bank composed of 12 IIR narrow-band notch filters to eliminate feedback.The strongpoints and shortcomings of all 3 schemes have been disscused in the last chapter.