The AION Modular 904A Low Pass filter is an Eurorack clone of the classic Moog Modular Low Pass filter (should not be confused with the Mini Moog Low Pass filter).
The 904A Low Pass filter attenuates frequencies above the Fixed Control Voltage (cutoff frequency) point at a rate of 24dB per octave. The cutoff frequency is voltage controlled through the three control inputs at the bottom of the module (1v per octave).
The Regeneration knob (resonance) varies the amount of internal feedback, creating a resonant peak at the cutoff frequency.
The Fixed Controlled Voltage knob adjustes frequency over 12 octaves span (1v per octave).
The Frequency Range switch sets the frequency band in two-octave steps:
1- 1Hz to 5kHz
2- 4Hz to 20kHz
3- 16Hz to 80kHz