Signal Meters - Polycom SoundStructure C16 Design Manual

Design Guide for the Polycom SoundStructure C16, C12, C8, and SR12

Signal Meters

8 - 10
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.
The input signal meter is labeled so that signals greater than -20dB will light
the first meter segment, greater than -16dB will light the second meter seg-
ment,..., and finally greater than +16 will 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 will illuminate when the
signal exceeds +20dB.
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.
To properly adjust the levels for microphones, adjust the analog input gains so
that during normal speech at the desired distance from the microphones two
yellow LEDs are reached by the peak meter and occasionally additional LEDs
are flickering above that. The VU meter should show a solid green LED at the
0dB level.
+20
16
12
8
4
0
-4
-8
-12
-16
-20