Using a Speech Codec to Suppress Howling in Public Address Systems

Ditter D, Berdahl E. Using a Speech Codec to Suppress Howling in Public Address Systems. In: AES Convention 142. Audio Engineering Society; 2017. Paper 9800. Available from: https://aes.org/publications/elibrary-page/?id=18674

@inproceedings{Ditter2017_18674,
  author = {Ditter, David and Berdahl, Edgar},
  title = {{Using a Speech Codec to Suppress Howling in Public Address Systems}},
  booktitle = {AES Convention 142},
  note = {Paper 9800},
  year = {2017},
  month = may,
  publisher = {Audio Engineering Society},
  url = {https://aes.org/publications/elibrary-page/?id=18674}
}

TY  - CPAPER
TI  - Using a Speech Codec to Suppress Howling in Public Address Systems
AU  - Ditter, David
AU  - Berdahl, Edgar
T2  - AES Convention 142
M1  - Paper 9800
PY  - 2017
DA  - 2017/05/06
UR  - https://aes.org/publications/elibrary-page/?id=18674
PB  - Audio Engineering Society
LA  - en
AB  - Acoustical feedback is present whenever a loudspeaker signal gets redirected to a microphone that feeds its input signal directly or indirectly back into the loudspeaker. If the gain around such a closed feedback loop is close to or higher than unity, unpleasant acoustical artifacts will typically occur and will nearly always lead to a periodic howling sound. Most readers are probably familiar with this noise, which can for example set in when a microphone is accidentally pointed at a speaker. This research project aims to suppress these unwanted effects of acoustical feedback by the insertion of a modified speech coder and decoder into the signal path of the feedback loop. It is demonstrated that the Speex open-source speech codec can be successfully tweaked to increase the maximum stable feedback gain by as much as 3 dB to 7 dB through adjustment of the codec’s quality parameter. This enhancement outperforms the simple introduction of shaped noise into the feedback loop and is compared with the performance of a frequency shifter. Tests are conducted using an automated experimental framework for determining the maximum stable gain of a public address system.
ER  -