Bi-Filter

Audio Mixer w/ phase switch (3x1) (AMX)
[The Audio Mixer is a three-in/one-out manual mixer with a phase switch on input 3]

Variable Slope VC Filter (VCFS)
The VARIABLE SLOPE VCF (VCFS) offers unique control of sound quality offered by no other synthesizer manufacturer. All VCFs offer voltage control of the cut-off frequency (i.e. control of which frequencies the filter lets pass). The VCFS allows the amount of filtering to be dynamically controlled as well, from barely perceptible filtering to highly resonant, sharp cut-offs. With the variable slope control in the center position, the VCFS acts as a typical flat-response VCF, with high-, low- and band-pass outputs available simultaneously. The slope of the cut-off is 12 db/octave. As the control is moved toward the maximum position, the resonance of the filter increases, so that the cut-off becomes sharper. Although the VCFS will not ring like the VCFQ, it will resonate enough at the maximum setting to pick out harmonics from a complex signal input. As the control is moved to the minimum position, the cut-off slope will decrease to 6 db/octave. This type of change of filter slope has been found to be an effective synthesis technique corresponding well with some of the transformations in acoustic instrument sounds. There are two signal inputs to the VCFS which can be mixed and manually cross-faded from the associated knob.

Variable Bandwidth VC Filter (VCF2)
The VARIABLE BANDWIDTH FILTER (VCF2) has a band-pass output which can be varied manually or with voltage control. This is a standard response synthesizer VCF, typical to filters used in many studio systems. In the VCF2, two state-variable VCF's are connected in series to produce a total of five outputs. High pass, low pass, two fixed bandwidth outputs, and one variable bandwidth output are available. The outputs are all flat-response (no resonance) so the VCF2 is suitable for processing concrete sounds without introducing resonant coloration to the timbres. Under voltage or manual control, cut-off frequency of the high and low-pass outputs are affected, as well as the center frequency of the two band-pass outputs. Both center frequency and bandwidth are independently controllable on the variable bandwidth output.

Dual VCA (2VCA)
The DUAL VCA (2VCA) employs two high-quality VCA's. This module is an excellent inter-patch VCA, featuring very low noise and exponential response. It was designed as a small VCA function for use at various places within a system for internal VCA functions (as opposed to the VCA's for output mixing). Like the new Universal Audio Processor and the Cross-Fader this VCA has an audio taper that is an exponential curve with a 12 db per volt sensitivity throughout the range except below about .5 volts. Below this threshold, the output of the VCA will decrease rapidly to completely attenuate the signal. This response is perfect for our envelope voltage range. and is responsible for exceptionally quiet operation. Control voltage rejection is very high, and the unit cannot be overdriven beyond a gain factor of two.

[Note that on this version of 2VCA, the top VCA is DC-coupled and the bottom VCA is AC-coupled]

Mixer / CV Processor (3x1) (MPR)
[Note: Similar to the Audio Mixer (AMX), the Mixer / CV Processor's inputs and output are DC-coupled with blue jacks, indicating that they can process CV or audio. The other differences are 1) rather than a phase switch, IN 3 includes a single level and polarity control, and 2) the output includes a DC offset control.]