I'm looking at using a modular synth to convert a single note guitar melody into basic sine waves at pitch.

I don't care about chords so that should simplify things quite a bit.

Problem is, I don't know what steps to use to simplify the signal. I've looked at EHX and other manufacturer's "synth" guitar pedals but they don't have the sound I'm looking for.

What do I need to patch and tweak on the synth to get what I need?

The modular synth I'm using is the Empress Zoia pedal.

EDIT: I switched to a BOSS SY-300 pedal. That gives me a guitar to sine wave conversion out of the box.

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    To attenuate all harmonics and keep the fundamental, use a steep low-pass filter. If the melody ranges widely, use a pitch tracker to adjust the filter's cutoff frequency. Then, if the pitch tracker is good enough, you could instead use it to drive whatever synth patch you like. Am I missing something? – Camille Goudeseune Oct 17 '19 at 21:42
  • @CamilleGoudeseune What's an example of a pitch tracker? – Von Huffman Oct 17 '19 at 22:41
  • Getting a guitar really sounding like a siney synth is a very tough job - one better suited to a more sophisticated guitar synth pedal (or (audio→MIDI)→synth), I would have thought. What pedals have you tried? – topo Reinstate Monica Oct 17 '19 at 22:48
  • Would quantization to the nearest semitone help? – pro Oct 18 '19 at 3:24

I am not certain you will find a set of patches on the synth that really make the guitar sound like a synth.

There's a fairly wide range of frequencies that a guitar can make, from about 82Hz at E2 (open, low E), all the way up to 1319Hz as E6 (24th fret, high E), on a 24 fret, 6 string guitar in standard tuning. You will probably not be able to find a set of high/low pass filters that will isolate all the harmonics of any note that can happen across that range, without affecting the fundamental frequency of the note as well.

Isolating the fundamental frequency is a different, and not entirely easy problem. Usually, some form of Fast Fourier Transform is used to get the fundamental frequency of the note that's being played, along with some sort of peak detection to figure out what volume that frequency should be output at. That all has not be done in real time, which is not a trivial problem.

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  • All of that has been done in real time from when I defended my dissertation, and from decades before. ideals.illinois.edu/handle/2142/35290 – Camille Goudeseune Oct 18 '19 at 3:32
  • I did not say at all that it's not possible, just that it's not a trivial problem. I currently have a number of software projects which do this in real time, it's just tricky to get everything to work properly. If it was trivial, or easy, to get good/workable real time results from analyzing frequencies, spectra, peaks and everything else of a polyphonic stringed instrument like the guitar, one would assume that such technology would be available somewhere; but MIDI guitar has yet to catch on. – whofferbert Oct 18 '19 at 4:32

As others have pointed out: why start with a plucked sound if you have all that synth gear and can create a sine wave from scratch?

In fact, Mr.Tech Wise Guy suggests you take your guitar note, feed it into a FFT, grab the peak frequency, which oughtta be the fundamental, and send that value to a sinewave generator.
(yeah, that's the same as a low-pass filter)

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  • The modular synth I'm using is the Empress Zoia pedal – pro Oct 18 '19 at 19:35
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    So the zoia has an oscillator, which AFAIK is the sine wave generator. It also has a pitch detector module. If you were to couple an envelope follower to a volume control, the volume will rise when you play harder (more voltage) and drop as the string decays or you pick softer. Not sure if the volume control is needed but this is basically what carl suggests, translated into what I see on the Zoia homepage. – Yorik Oct 18 '19 at 21:01

You can do this many ways. For Max/MSP there's an external object called sigmund~ that can split your signal to components and pitch track and envelope track it. It seemed to work pretty well, but you'll have to build the Max patch yourself, and there's a bit of latency. The chain of objects is something like: audio plugin~ --> sigmund~ --> sig~ --> mtof~ --> cycle~ --> *~ --> plugout~

For the multiplication (*~) you take the envelope output.

Another way to do almost the same is with MIDI Guitar 2 by Jam Origin, which has an effect called Deep Expressor. It splits the signal to its component harmonics and allows you to mix the harmonics with the original signal in various ways. For example the "flute" preset only takes the fundamental frequency. MIDI Guitar 2 Deep Expressor

The incredible thing about this is that it's... polyphonic! But there's a bit of a slow attack if you want to only get the root harmonic. I couldn't figure out how to get the "sustain" part to start with no slow attack, and without using any of the "plucktone".

https://www.jamorigin.com Take a look at the video showing how Paul Bielatowicz of ELP Legacy uses the software.

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