The Model 612 Expander/Noise Gate is a true dual channel expander using downward expansion with a variable ratio (1.2:1 to 30:1), thus allowing an infinite variety of dynamics control which are impossible with a gate. High and Low pass filters on the KEY input allow frequency selected gating. With high ratio, the Model 612 becomes the world's finest gate. It is also a ducker, allowing a KEY input to lower the level of the primary audio input. The heart of the Expander/Gate is the Aphex VCA 1001 which will not click regardless of attack or release time! Attack time as low as 4 microseconds (wavefront dependent). Absolute stability prevents settings from wandering. XLR-type Servo-Balanced I/O means foolproof installing with balanced or unbalanced systems.