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AFR - Acoustic Feedback Reduction

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About Acoustic Feedback Reduction

Acoustic Feedback happens in an electro-acoustic system when there are simultaneous couplings:

  • electrical coupling between the system microphone;
  • acoustic coupling between the loudspeaker and the microphone.

The two couplings potentially create a signal loop with a signal being amplified on each cycle reaching quickly the maximal possible level. This situation is often occurs in sound reinforcement systems, hearing aids, wired speakerphones, intercom systems and others.

Alango Acoustic Feedback Reduction (AFR) technology significantly alleviates the problem of acoustic coupling in sound reinforcement systems. Patent pending Quasi Proportional Frequency Shifting (QPFS) technology introduces a small, unnoticeable change in the pitch of the loudspeaker sound. Compared with a simple frequency shift, QPFS approximately keeps the correspondence of original sound harmonics thus introducing much smaller sound distortion. Comparing to general pitch shifting technologies QPFS has much smaller processing delay and thus can be used in real time system where the talker immediately hears himself via the microphone. The frequency shift effectively breaks possible signal loops without introducing noticeable distortions into the sound.

Figure 1. Acoustic feedback explanation


AFR technology is very compact requiring relatively small number of MIPS and RAM memory. The exact numbers depend on the sampling frequency. The associated processing delay is about 5 ms.

Platforms availability

Real time demo of Alango Acoustic Feedback Reduction technology is currently available on TMS320VC5510 evaluation board. Porting to other computation platforms is simple and straightforward.

White papers

AFR technology white paper >>

Additional information

More detailed technical information and examples are available upon request.


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