Definition Of Terms - Polycom Vortex EF2280 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 to be heard by the
remote participants.
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 cancel-
ler can cancel per unit time, typically expressed in dB/sec. Better echo cancel-
lers 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 micro-
phone-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 hardwired 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 preforms processing to eliminate the echo from the signal.
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EFINITION OF ERMS
EF2280 Reference Manual