Moon Modular - 517 Coupled Dual VC High Pass / Low Pass Filter

The 517 features two extremely smooth filters with high-pass and low-pass modes. Their edge steepness is -18 dB respectively -24 dB per octave. Via a switch, both filter stages can be combined to create bandpass or notch characteristics. Wiring them in serial is possible as well. By doing this, users can create more steep or dual peak high-pass and low-pass filter designs. In addition to cutoff frequencies and resonance values, the spread and balance of both filters are adjustable. Furthermore, it is possible to modulate all parameters mentioned.

The 517 features two identical filters. The topology is based on circuits known from the Oberheim Xpander and the OB-XA. Each filter comes equipped with cutoff and resonance potentiometers as well as a switch for choosing between high-pass (-18 dB per octave) and low-pass mode (-24 dB per octave). Furthermore, there are two CV inputs for cutoff modulations. One of them features a bipolar attenuator. The resonance is equipped with one control voltage input. Besides separate audio inputs and outputs, there is a connector which emits the signals of both filters in combination.

The 517 offers four modes of operation. While the module is in Separate mode, both filters can be used independently from each other. Normalized audio and CV inputs make parallel and stereo processing very easy. With opposite modulations, cool pan effects can be achieved. Using the other modes of operation, both filters can be linked to create band-pass, notch or steeper high-pass respectively low-pass characteristics. (High-pass = -36 dB per octave / Low-pass = -48 dB per octave) The cutoff and resonance potentiometers of the second filter channel are deactivated in this mode. Using the bandwidth knob, the cutoff frequencies of the filters can be shifted in opposite directions. This makes it possible to adjust, for example, the width of the band-pass or to create a high-pass respectively low-pass with two stages and resonance peaks. The balance of the filters can be adjusted as well. Besides potentiometers, Bandwidth and Balance parameters feature CV inputs.