Polycom EF2201 Brochure & Specs page 11

Should I leave the AGC on all the time?
Yes. We have done extensive testing of the AGC and it can dramatically improve the quality of an audio conference. We
recognize that your experience from other AGC's may not be that favorable, but we definitely suggest you leave the
Vortex's AGC on all the time because it is very robust. When InstantDesigner creates the design, it will enable the input
AGC will configure it with a +/- 3 dB gain range by default.
Automixer Questions
What style is the Vortex's automixer?
The automixer (or more accurately, both automixers) in the Vortex use a gating style of automixing. The automixers make
a determination of which signals should be gated on and this decision gets translated into a decision of what gain to
apply to the input signal as it gets mixed with other signals to create an output signal in the matrix. The automixer takes
in up to 8 microphone/line inputs and produces 8 line output signals and gain information to be applied to each of these 8
gated outputs as they are used in the matrix. The matrix does the actual mixing of the signals, but the automixer
determines the gains for the signals. If you select the gated version of an input at a cross point in the matrix then you
will get the signal scaled by the gain that the automixer has determined should be applied to that signal.
What parameters can you control?
There are a number of parameters to control and they are categorized as global parameters, mixer parameters (remember
there are two automixers), and channel parameters. The global parameters are hold time, decay time. The mixer
parameters are maximum number of open microphones, last mic mode, chairman microphone mode, and the amount of
off attenuation. The channel parameters are which mixer the input is assigned to, the gate ratio, adaptive or fixed
threshold, manual threshold, and the gate priority. Details of these options are given in Section 9: Automatic Microphone
Mixing.
What is different about it?
The noise canceller helps remove noise so the gating decisions can be made more intelligently. The speech detector in
the noise canceller also helps to determine whether the channel should gate on.
What about NOM attenuation, can I use it over 8 units?
NOM stands for the number of open microphones and NOM attenuation means the attenuation applied to a sum of
microphone signals to compensate for having some number of open microphones. With the Vortex, NOM attenuation
can be applied to each output signal that is made up of sums of the input microphones. For instance if an output contains
microphones 1-8 which have been automixed and 3 of these microphones are currently open, then an attenuation of
=
10 log ( ) 3 . 4
10
the other signals that make up that output.
Now, if you have multiple Vortexes, information about the number of open microphones can be sent to other devices by
using the W, X, Y or Z busses. This means that an output signal made up of microphone signals from linked devices will
have the appropriate NOM attenuation applied to the output signal:
open microphones from all the linked devices being summed together to form that output. So yes, NOM attenuation can
be applied across all 64 available microphone channels.
I
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dB can automatically be applied to the sum of these microphones before they are summed with
10 log ( NOM )
where NOM is the number of
10
9