Symetrix 425 - Paging with Ducking; Stage Monitors

8.4 Paging with Ducking
Many situations involving a "talking host" and any sort of musical background will require the
background music to drop in level whenever the host signal is present. By splitting the host
signal, part of it can be used to tell the 425 when to take action and lower the background
source by an amount determined by the threshold control.
MICROPHONE
PAGE
INPUT
MIC
INPUT
LINE
OUTPUT
AUDIO
INPUT
SIDECHAIN
SPLITTER
MIC
INPUT
AUDIO
PMA
PRE-AMP
DUAL
LINK
LIMIT
COMPRESSOREXPANDER
-20
+5
THRESHOLD (dBu) RELEASE
FAST
SLOW
-18 -12 -6 -2
-10 -12 -15 -25
-40
-10
BYPASS
RATIO (X:1)RELEASE
1
10
2
-8 -6 -4 -2
FAST
SLOW
-12 -9 -6 -3
+5
BYPASS
-10
GAIN (dB)
BYPASS
IN
0
+20
STEREO
DUAL MONO
CLIP0VU-10 -20 STEREO
OUT
BYPASS
-5 -30 +10 -25
THRESHOLD (dBu) THRESHOLD (dBu)
-2.5 +12.5
+10
+5 +15
1.3 2.5
q Set the compressor threshold so that all the gain reduction LEDs for the compressor are illuminated
when the host speaks. Although the display won't show it, you can set the threshold control even
lower for more ducking action.
q Use the release control to vary the speed at which the music returns when the host stops talking.
8.5 Stage Monitors
Public address and sound reinforcement situations that require comp/limiting are often
plagued by feedback problems. The overall increase in level that results from compression can
cause feedback in the absence of signal, when the compressor releases and brings levels back
up to normal.
COMPRESSOREXPANDER
-20
+5
THRESHOLD (dBu) RELEASE
FAST
SLOW
-18 -12 -6 -2
-10 -12 -15 -25
-40
-10
BYPASS
RATIO (X:1)RELEASE
1
10
2
-8 -6 -4 -2
FAST
SLOW BYPASS
-5 -30 +10 -25
THRESHOLD (dBu)
1.3 2.5
q Set the compressor threshold for no more than 9 dB of gain reduction on normal signals.
q Set the expander threshold for 16 dB (or more) of gain reduction when the signal source is silent,
and 0 dB of gain reduction when the signal is present.
q Use the release control to make the expander follow momentary pauses.
q Since the successful implementation of this technique requires careful settting of the two threshold
controls, be prepared to fine tune the settings to match the levels of your system and the vocalist's
style.
Rev 2.0, 10/29/93
8-2