Input Signal Level Adjustment; Signal Meters - Polycom SoundStructure C16 Design Manual

SoundStructure devices may have gain applied in various positions throughout the signal chain as shown
in the following figure. Gain may be applied in the analog input gain stage, the input fader, the matrix, the
output fader, and the output analog gain stage.
The analog input gain is applied in the analog domain to the analog input signal to adjust the signal level to
match the level required by the Analog to Digital converter to properly digitize the signal with the required
signal fidelity.
Applied Analog Gain in Signal Chain
Analog Gain
Analog Input

Input Signal Level Adjustment

The analog input gains are adjusted with the input gain slider on the SoundStructure Studio channels page.
Any slider adjustments cause the mic_in_gain command to be executed. The analog input gain slider
provides an adjustable range from -20 to +64dB of gain in 0.5dB gain steps and has a meter that shows the
input signal activity from -20 to +20 dBu as shown in the following figure.
The purpose of the analog input gain is to provide enough gain to get the input signal to the 0 dBu nominal
signal level of the SoundStructure devices and have additional headroom for the signal to peak above that
level.
Analog Input Gain
The input signal meter is labeled so that signals greater than -20dB light the first meter segment, greater
than -16dB light the second meter segment, and finally greater than +16 light the tenth meter segment. In
this sense, the meter segment label represents the minimum signal level required to light the meter
segment. The clip indicator at +20 illuminates when the signal exceeds +20dB.

Signal Meters

The meters on the SoundStructure devices show a VU average signal level with a peak meter overlaid on
the VU meter. The VU meter drives the meter segment display while the peak meter shows the maximum
amplitude. The peak meters conform to the IEC 60268-18 standard and have a 12dB/second decay from
the peak signal levels.
Polycom, Inc.
Digital Processing
Input
A/D
Processing
Input Fader
+20
16
12
8
4
0
-4
-8
-12
-16
-20
Matrix
Output
Processing
Output Fader
Analog Gain
Analog Output
D/A
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