Karplus-Strong Resonator

Based off the Karplus-Strong algorithm, this is a resonator built from a delay line and a filter in the feedback loop.

If no input is connected to the In jack, the module also has its own internal exciter, which can either use white noise or a pluck when the G/T/VCA jack is given a trigger or gate. Triggers will give short plucked sounds, and gates will give longer bow type sounds. In addition to this it is possible to use this as a VCA, and thus signals from envelopes can be fed into this jack too.

When the input jack is connected, the internal exciter is disabled, and the external audio is fed straight into the exciter. The dry/wet balance of the final audio is controlled by the mix knob, and both the dry and pre-exciter signals pass through a VCA.

Parameters

• Mix/Decay - When an external input is connected, this sets the dry/wet balance of the input signal. When using the internal exciter, this sets the decay length of the internal envelope.
• Pitch - sets the pitch of the delay line to +-12 semitones. The pitch jack takes a V/Oct signal.
• Switch - Exciter pluck/noise(bow). When using an external source this sets if this goes through a lowpass filter before entering the resonator.
• Cutoff - Delay feedback cutoff frequency
• Fb - Delay feedback
• Vol - Controls output volume

Ideas

For a simple plucked string sound, attach the pitch input to V/Oct and the G/T/VCA input to a trigger. Set the mix/decay knob to minimum.

To drive the resonator from an external source, connect an input, set the mix knob to maximum, and hook up pitch and G/T/VCA to your V/Oct and gate/envelope sources.

To use as a VCA/Clipper, attach your audio source and set the mix/decay knob to minimum. Attach a gate or envelope control voltage to G/T/VCA.