The Development Of Automatic Acoustic Feedback Suppressor

Howling is often found in sound-amplifying systems, which results from acoustic feedback. It restrains sound-amplifying systems'gain from increasing. When feedback is serious, the sound-amplifying systems even cannot work. Traditional feedback exterminating methods consist of improving rooms'acoustic property, cascading an equalizer or a frequency-mover in the sound amplifying link, etc. These methods hurt the normal sound, only improve the system gain a little and are not easy to operate. Recently, digital signal processing technology develops greatly. A new generation of automatic acoustic feedback exterminator appears. It overcomes old feedback exterminators'shortcomings, does little harm to speech and music signals, improves the systems'gain prominently and is easy to operate. Nowadays, most of the feedback exterminators available are imported from oversea, which are expensive. If we develop a feedback exterminator with intellectual property which can replace foreign products, we can apply it in multimedia classrooms, meeting rooms, etc. Based on the application ground, we put forward a scheme for automatic acoustic feedback exterminator. This scheme is particular in the following aspects: Firstly, we adopt FFT algorithm to analyze signals coarsely and Chirp z-Transformation (CZT) to analyze signals precisely. The system's frequency resolution can obtain 2 Hz. Secondly, we adopt an algorithm suitable for designing IIR filter on DSPs.The algorithm can design high frequency-selective IIR filters and is not time-consuming. For implementing IIR filters on a fix-point DSPs, it rescales filters'cofficents properly to prevent overflow. Chapter 2 of this paper introduces the characteristic of acoustic feedback signal and the principle of automatic feedback exterminator. Chatper 3 introduces the system's hardware architecture. Chapter 4 introduces software flowcharts and key algorithms.