Design Guide for the Polycom SoundStructure C16, C12, C8, and SR12
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as shown in the following figure. The telephone input and output can be con-
figured to have different equalization.
To enable a filter, click the check box next to the filter. This will make the filter
the active filter and allow the parameters to be changed as shown next.
The cut off frequency can be adjusted between 0 Hz and 20,000 Hz, the order
can be adjusted from 2
nd
to 8
th
, and either a Butterworth or Linkwitz-Riley
filter may be selected.
For each of the 1 parametric filters, the designer can choose from:
• Parametric filter
• Notch filter
• Allpass filter
Parametric filters emphasize or de-emphasize the center frequency with a gain
and bandwidth setting. The user can specify the bandwidth (in octaves), center
frequency (in Hz), and gain (from 0 to 20 dB).
Notch filters eliminate energy (attenuate only) at the center frequency. The
amount of attenuation for the signal is determined by the bandwidth (in
octaves) selected. The bandwidth is defined as where the gain is -3 dB.
Allpass filters do not modify the gain of the signal, but change the phase. For
a second order allpass filter, the phase shift is 0 degrees at 0 Hz, 360 degrees at
high frequencies, and 180 degrees at the center frequency. The bandwidth is
defined as the bandwidth (in octaves) where the phase shift is 90 degrees and
270 degrees.
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