- In 1
- controls the level of input 1
- In 2
- controls the level of input 2
- In 3
- controls the level of input 3
- controls the cutoff frequency of the filters
- controls the resonance of the filters
- Key-CV Track
- controls how much the Key-CV influences the cutoff frequency of the filter.
- CV Depth
- controls how much the CV influences the cutoff frequency of the filter.
- Audio input 1.
- Audio input 2.
- Audio input 3.
- Envelope modulation control
This is a superb sounding voltage controlled filter module that is based upon the work of Bob Moog in the 1960s. It uses the classic ladder design implemented with transistors and passive feedback control. However, I have made all four rungs of the ladder available as outputs. At first glance this seems to offer just a choice of 1, 2, 3 or 4 pole outputs. The 4 pole output producing a smoother sound due to the greater steepness of filter slope. But, it is also possible to mix these outputs together to create new and interesting responses including varying degrees of band pass filtering. The Oakley MultiMix module provides an easy way of doing this, since you can subtract and add signals together.
The filter uses matched NPN pairs to minimise CV breakthrough. It has a resistive feedback network utilising a reverse log pot especially made for Oakley Sound Systems by Omeg. This gives a smooth transition when turning up the feedback/resonance control. I have made the feedback input available from the front panel. With no jack inserted, the feedback takes its signal from the 4-pole output. This connection is broken when you insert a jack to allow other modules to process the filter output before it is fed back. Insertion of a non-linear element like the WaveFolder produces fantastic new timbres.
The filter has temperature compensation, and the VCF can be used as a sine wave oscillator across the whole audio band and beyond.