Processing and Control for Professional AV Installations
Legacy Hardware

421m AGC-Leveler

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.

FAQ

On the 421m, the AUTO RELEASE THRESHOLD may be set too high. Turn this control further counter-clockwise. Additionally, the EXPANDER THRESHOLD may be set too high. Turn this control further clockwise.

On the 422, the DETECTOR THRESHOLD may be set too high. Turn this control further counter-clockwise.

The units will not attempt leveling action on a sine wave or pink noise because they do not recognize a sine wave or pink noise as true audio. To test the units, you must use a real-world audio source, such as music or speech.

You may have the RATIO control set too low. Try turning it up to around 4:1.

Set the Limiter THRESHOLD control so that the LIMITER LED just flashes occasionally, on peaks in the music. If you need more leveling action, turn the RATIO control up to 4:1 or higher.