How the feedback suppressor works

2021-01-27

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The howling of the audio system is caused by the continuous enhancement of certain frequency points in the audio signal due to the positive feedback. If these frequency points are cut or greatly attenuated, the acoustic feedback can be effectively suppressed. The feedback suppressor is designed according to this idea, and its working principle is: use computer technology to quickly scan, automatically find the audio signal frequency (ie howling frequency) where howling occurs, and automatically generate a set of these howling frequencies The same narrow-band filter cuts the howling frequency, so as to achieve the purpose of automatically suppressing howling and eliminating acoustic feedback.

The feedback suppressor is composed of amplifier, A/D converter, narrowband digital filter bank, digital signal processor, feedback center frequency detector and D/A converter, as shown in the figure below.

After the audio signal is amplified by the amplifier and converted into a digital signal by the A/D converter, it is sent to the digital signal processor and the feedback center frequency detector; the feedback center frequency detector continuously scans the input digital audio signal, using the center The fast scanning method provided by the microprocessor CPU automatically searches for the howling frequency; once the howling frequency is found, the CPU will immediately control the digital signal processor to set this frequency, and use a narrow-band digital filter with the same frequency to remove or Attenuate this frequency signal, thereby suppressing acoustic feedback howling.

Although the narrow-band digital filter filters out the howling frequency, this frequency in the audio signal is also filtered out, but because the frequency band of the narrow-band digital filter is very narrow, the process of filtering out the howling frequency affects the audio signal. The influence of the frequency spectrum is very small, so it hardly affects the sound quality of the audio signal.