Oberfilter

Included in the MRB Luxury Filter Bundle

Demo sounds are on the Oberfilter Bundle page.

The MRB OBERFILTER is a software clone of the filter found in the 1973 Oberheim Synthesizer Expander Module (SEM), but with extra features (as you have come to expect from MRB). Unlike the 4-pole (-24db/oct) cascade Moog and ARP lowpass filters of the day, the SEM filter was a 2-pole (-12db/oct) state-variable design that featured lowpass, highpass, and band-reject (notch) responses, with a clever knob that swept through them. Bandpass was also available. It did not self-oscillate. The SEM in monophonic and polyphonic collections were used by the likes of Jan Hammer and John Carpenter on various movie scores, as well as by Rush, Styx, VanHalen and Herbie Hancock. Check out the Oberheim 4-Voice and 8-Voice systems on the web for a look at these much-sought-after behemoths. The original SEM went out of production in 1980. The OB-X contained a version of this filter, but not the OB-8.

MRB Features: In the original design, turning the knob from lowpass through notch to highpass results in the resonance (Q) being lost when passing through the notch position. We provide a switch called PEAK which flips the notch into a peak, thus maintaining resonance. It's just another interpretation of what the middle response should be. One isn't necessarily better than the other and they do sound completely different so having the choice is nice. You can also voltage control your way through the responses using the LNH CV input. Be aware that a frequency swept notch is best heard at low Q. At high Q, the notch is so narrow that it becomes inaudible. Separate lowpass, bandpass, and highpass outputs are also provided.

A DRIVE control with CV acts as an input VCA (you can actually use this as your patch VCA if you want). Activating the CLIPping switch produces harmonics, sidebands and grit. The DRIVE VCA is wired before the CLIPper so your grit can be voltage controlled.

We all know that the heart and soul of any subtractive synth is the filter. You just never can have too many. Now there's nothing to stop you from putting multiple OBERFILTERS in parallel or cascade to create more complex resonant structures, unique percussion, vocal sounds and outright craziness. Hardware users can only stare back in awe.