Original Vintage Style Noise-Gate / Expander.
The BT ExpanderGate GX622 tames the noise floor so that you hear only the audio you want to keep. This fully-adjustable gate/expander reduces (or cuts) the signal if the level becomes too low (as determined by the Gate Threshold setting). This controls unwanted background noise on the track (s).
Like a compressor, the Attack and Release controls determine how fast the gate opens and closes. To help the gate decide when to open, you can use the two Filter controls (Side Chain).