Guitar Synth for Voltage Modular

[utdgrant]

I've been messing around with phase-locked loops and frequency counters to try to create a reliable pitch extractor. Alas, my experiments proved unsatisfactory. Instead, I decided to try manipulating an external signal's waveform directly, like an old-skool octaver pedal. This provided more solid and responsive tracking.

GuitarSynth.jpg (451.55 KiB) Viewed 4789 times

The external signal is amplified and low-pass filtered in order to attenuate upper harmonics. The filtered signal is then fed into a Schmitt Trigger circuit formed by two ACE Comparators and an ACE S-R Latch. The output from the S-R Latch is a square / pulse waveform which tracks the fundamental frequency of the input.

The square signal is then fed into the Gate Input of a Big Rat to give it more of a sawtooth shape. It is also fed into two cascaded divide-by-two counters to give a square sub-octave and -2 sub-octave. By combining different signals with AND gates, I also derived 25% pulse waves at -1 and -2 octaves. All these signals are available simultaneously in a Six-Input Mono Mixer. The mixer output is fed through a Smol Rat to remove the DC Offset, and fed to the input of a resonant low-pass VCF.

The VCF can be driven by an envelope follower, acting on the external input signal. Alternatively, there are two ADSR envelope generators which can be used to drive the VCF and a VCA.

I think the end result is quite decent. It works particularly well with monophonic inputs, particularly singing.

Here is the patch:

DirectWaveformGuitarSynth.voltagepreset

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I've made a couple of YouTube demos:

Guitar as Input

Vocals as Input

[UrbanCyborg]

Totally strange, Grant.

Reid