421m
1
IntroductionChapter 1
Front panel
Rear panel
The Symetrix 421m is a wide-range AGC-Leveler, a peak limiter, and a downward expander that
features a microphone preamp, eliminating the need for a separate outboard microphone preamp in
some applications. The 421m reduces the dynamic range of its input signal by the amount of its
ratio setting. That is, if the ratio setting is 2:1, then 40 dB of input range turns into 20 dB at the
output. A fast peak limiter puts an absolute ceiling on the output level so you know that peaks are
held to the level that you set. A downward expander reduces the gain when signal levels fall too
low to process, reducing the noise buildup at low signal levels. Speech filters allow a reduction of
reduction the bandpass of the 421m to minimize feedback or amplifier power waste caused by
spurious out-of-band signals.
AGC-Levelers can be used anywhere that you might need to reduce the dynamic range of an audio
signal over a wide range of signal levels. Possible applications include: tape duplication (especially
cassette), driving telephone lines, driving broadcast or STL transmitters, podium or lectern micro-
phones, paging systems, unattended sound systems, and music recording.
The 421m is listed by Underwriters Laboratories Inc. (UL). Samples of this product have been
evaluated by UL and meet the applicable UL Standards for Safety.
We recommend that you read this manual from cover to cover. Somewhere between the confines of
the two covers you should find the answers to most of your questions. If not, please feel free to
contact our Customer Service department via phone, fax, or e-mail for answers to your questions.
The numbers are:
Telephone:(425) 778-7728
Fax:(425) 778-7727
E-mail: symetrix@symetrixaudio.com
Web site: www.symetrixaudio.com
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
TYPICAL
CONNECTIONS
LYNNWOOD, WA, USA
MANUFACTURED IN
POWER
==
PIN3
XLR
RING
PHONE
LOW(-)
SIGNAL
==
XLR
PIN2
PHONE
TIP
SIGNAL
HIGH(+)
GROUND
SIGNAL
=
SLEEVE
PHONE
=
PIN1
XLR
GND
EARTH
GND
SIG
GND
SIG
BALANCED/UNBALANCED LINE OUTPUT
LEVEL
TRIMTRIM
BALANCED/UNBALANCED LINE INPUT
OFF
+48V
PHANTOM
CONNECT TO
SYMETRIX 421 ONLY!
(NOT A MIDI CONNECTOR)
STEREO LINK
BALANCED MICROPHONE INPUT
LEVEL
POWER
MAXIMUM
AC INPUT
20 WATTS
+50+250-10
421m
AGC-LEVELER
OUTPUT LEVEL
SYSTEMSPEECH CURVEOUTPUT LIMITERAGC-LEVELERDOWNWARD EXPANDER (NR)
421m
AGC-LEVELER
AUTO
BYPASS
RECOVERY
AUTO-RELEASE
BYPASS
BYPASS
IN
IN
125Hz 6kHz
LEVEL
RATE
2:1
-54
-54 CLIP
INCREASE
DECREASE
-48 -42 -36 -30 -6 -12 -18 -24 +12 +6 0VU
FAST
SLOW
IN
BYPASS
ACTIVE
BYPASSSTEREO LINK
0
BYPASS
-15
THRESHOLD (Vu)
-8 +15
LIMIT
SLAVE
MASTER
EXPAND
0VU +6 +12 -24 -18 -12 -6 -30 -36 -42 -48
-45-20
BYPASS
INPUT LEVEL
IN
BYPASS
TARGET OUTPUT LEVEL
HIGH
LOW
4:1
RATIO
SLOW
FAST
RELEASETHRESHOLD (Vu)
-35
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