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Voice-activated AGC for teleconferencing

In a group teleconference, sound pressure levels at the microphone vary due to variations in speaking distances and loudness. The conventional automatic gain control (AGC) appropriately adjusts the microphone gain so as to achieve a constant level. However, due to the lack of discrimination between speech and nonspeech sounds, nonspeech sounds can cause the gain to increase, giving rise to "noise pumping" or big increases in the background noise when no one is talking. In this paper, an AGC is described which uses a speech detector that examines stationarity of pitch and energy to discriminate speech against sounds like air conditioning, doors closing, footsteps, etc. For any gain increase to occur, a positive speech detection must be declared, thereby eliminating any "noise pumping" artifacts.