Polycom Vortex EF2280 Reference Manual page 57

Echo Canceller
EF Bus
Equalization
Line Echo
Macros
Matrix Mixer
Noise Cancellation
NOM
NOM Attenuation
NOM Bus
Presets
© Polycom, Inc.
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.
The EF Bus is a digital bus that includes the W, X, Y, and Z audio busses as well as
the echo canceller reference and remote control information. It can be used to link
multiple EF2280 devices.
Equalization is the process of adjusting frequency characteristics of an audio signal.
Line echo is caused by reflections of the audio signal from the telephone hybrid. The
EF200 Phone Add is an example of a unit that has a line echo canceller.
An arbitrary set of commands that can be replayed.
A matrix mixer allows you to choose which inputs are included in each output. Some
matrix mixers allow you to assign crosspoint gains to the inputs.
Noise cancellation is a digital signal process that removes noise from an audio signal
corrupted by real-world interferences such as HVAC, office noise, crowd noise, or
road noise. Generally, there are two parts of a noise cancellation algorithm: a method
to detect the noise and a method to remove the noise. The Polycom noise cancellation
algorithm (patent pending) is capable of removing 10 dB or higher of noise with no
degradation at all to the resulting speech signal. This method does not attenuate
speech, and removes noise during both speech and idle periods.
NOM refers to the number of open microphones in a system.
NOM attenuation is the gain applied to the overall system gain to the microphone sig-
nals to compensate for how many microphones are open. The amount of attenuation
is calculated by 10*log (NOM).
10
A NOM bus carries signal information as well as NOM information (i.e., the number
of open microphones in the system, NOM).
Presets correspond to configuration parameters that have been previously saved to
EEPROM.
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