PictureTel Concorde 4500 Servicing Manual page 61

Audio Board
The AI board also performs the following functions:
Provides the interface for audio to the monitor.
Controls and mixes the audio input to the keypad
microphone(s), PowerMic, optional tabletop or lapel
microphones, line-level input (from an external microphone
mixer) or a VCR.
Provides acoustic echo cancelation for the combined conference
room signal and telephone line signal.
Implements the conference control keypad interface for the
wired keypad.
Controls and mixes the audio outputs (line out for room audio
and a VCR).
Provides line echo cancelation for the telephone interface
board.
Supports Automatic Noise Suppression.
Supports Automatic Gain Control.
Converts analog audio inputs to digital representation.
Controls digital audio compression and decompression.
Supports digital to analog audio conversion.
2-15