: Global control for the built-in spring or digital reverb effect.
If you are waiting to find your manual or prefer a digital reference, here is the condensed setup guide based on the official . audio choice qm4 manual
Being a passive mixer, there is a natural "insertion loss" of signal strength (typically around 6dB to 10dB). You may need to turn up the gain on your amplifier or powered speaker to compensate. : Global control for the built-in spring or