Symetrix 422 Stereo Automatic Gain Controller Leveler Compressor
If the ad is up the item is still for sale. Excellent condition, tested and working. For radio/broadcast applications, recording, and live performances. You cannot hear the compression or the upward leveling working. Excellent in its transparency. Great when combining multiple sources together..
The 422 is a singular solution for controlling unpredictable stereo (or monaural) audio levels in a wide variety of audio systems. Application environments include broadcast, recording, tape duplication and installed foreground and background systems just to name a few. The 422 excels at subtly and unobtrusively bringing level divergent audio into a target window , resulting in greater intelligibility and informational perception. Unlike compressor/limiters, which are effective at reducing sounds that are too loud (pushing down from the top only), the 422 provides both downward compression and upward leveling by gently adding gain to low level signals until a target level is reached. The 422 employs advanced analog signal processing technology executed with high quality industrial grade components to meet, or exceed, the highest professional audio industry standards in terms of headroom, low noise and distortion, and superb sonic qualities.
Here is the brief Manual: http://pdf.textfiles.com/manuals/STARINMANUALS/Symetrix/Manuals/422.pdf