Distributed Automatic Volume Control (DAVC)
From Zenitel Wiki
The Distributed Automatic Volume Control (DAVC) is an algorithm which is using one or more microphones to measure the ambient audio/noise level, and adjusts the loudspeaker output level of the PA amplifier according to the ambient audio level.
The DAVC feature is available as from Turbine firmware 4.11.
To configure the DAVC, select Advanced AlphaCom > DAVC Settings.