MMF is a 2 pole Multi-Mode Filter in 4 HP. It has simultaneous LowPass, BandPass and HighPass filter outputs.
MMF will self oscillate into a nice sine wave and track 1V/octave. The Resonance is voltage controllable.
The PING input is for a gate or trigger, and generates a fast decay envelope with a nice sound, reminiscent of a vactrol filter, but without the vactrol. PING can normal to the FM jack, or go direct (switchable behind the panel).
The FM input is connected to an attenuverter pot to give you control over the signal.