Definition Of Terms - Polycom Vortex EF2241 Reference Manual

D
EFINITION OF
Acoustic Echo
Acoustic Gain
Ambient Level
Automatic Gain
Control (AGC)
Automatic
Microphone Mixer
Convergence
Rate
Crosspoint Mix
Minus Bus
Echo Canceller
© Polycom, Inc.
T
ERMS
Acoustic echo occurs in a conferencing or distance learning system when the remote
speech played in the loudspeakers is picked up by microphones in the room and is
transmitted back to the remote end. This transmitted signal is a delayed version of the
original, which causes the echo.
Acoustic gain is a term used in conjunction with sound reinforcement. It refers to
how much louder the audio is with sound reinforcement compared to without sound
reinforcement.
The ambient level, also referred to as noise floor, is the background noise heard in a
room when no one on the near or remote end is talking.
Automatic gain control increases or decreases the gain on an audio signal to an
acceptable value.
A microphone mixer that turns microphone channels on and off based on the signal
level going into the microphone.
Convergence rate refers to the amount of echo a line or acoustic echo canceller can
cancel per unit time, typically expressed in dB/sec. Better echo cancellers have a
higher (faster) convergence rate. This term is typically used to quantify the time it
takes to completely remove the echo from a conferencing system. Echo occurs due to
a complete change of the acoustic environment such as the beginning of a phone call
in a conference, a change of microphone-speaker placement, or speaker volume
adjustment.
A mix minus bus allows each device (i.e., a Vortex device) to create a mix of signals
without its own. Each device in the system can create four mixes (W, X, Y, and Z)
and place them on the bus. Each device also can create three mixes each from the W,
X, Y, and Z busses of the other devices (for a total of 12 mixes). One mix is hard-
wired as a normal mix minus. That is, it is a unity gain mix of the signals from all
other devices. The other two mixes can have crosspoint gains on the signals from the
other devices.
An echo canceller estimates the echo in an audio signal by using a reference and pre-
forms processing to eliminate the echo from the signal.
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EFINITION OF ERMS
EF2241 Reference Manual