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How to wavefold without wavefolder module?
MUFF WIGGLER Forum Index -> Eurorack Modules  
Author How to wavefold without wavefolder module?
I think I understand in principal how to wavefold a signal, using a rectifier, adding gain, and mixing it back in with the original signal. This certainly give me somewhere in the region of a single 'fold', but is it possible to create the multiple folds that a dedicated wavefolder module will create? What are wavefolder doing that a rectifer is not to add multiple folds?
I am curious to know more about this electronically-- I have some observations based on how I've managed to patch it and things I've learned (or at least partially understood) from Rob Hordijk.

If I am not mistaken, he gives a few clues in this talk: waveshaping is always dependent on amplitude and it works somehow by FM of 0 pitch which goes way beyond my understanding of how or what that means. Rob Hordijk on Waveshaping

I think this kind of sound is 100% different from the kinds of sounds you get from the kinds of harmonic waveshaping between even/odd harmonics, but I'm not certain.

Here are a few threads with workable waveshaping patching strategies:
Waveshaping with Optomix V2

Waveshaping with Maths

Waveshaping with Moddemix
It is usually using multiple stages, one folder or rectifier followed by another.
Previous threads with good reading about this:
Try running your signal through a quantizer and subtracting the original signal from the quantized version.
Try running your signal through a quantizer and subtracting the original signal from the quantized version.

This is great - never thought of this. Must try!

Instead of a quantiser, why not a S&H?

Now I’m wondering how to insert a Comparator controlling a S&H so that above a certain level the fold (subtraction) happens, but otherwise it doesn’t?
Running a signal through a quantizer is similar to bit rate reduction on a bitcrusher.

Running a signal through a S&H is similar to sample rate reduction on a bitcrusher, with the sample rate determined by the clock signal.

Wavefolding is just one form of waveshaper. You can accomplish it by running a signal through an amplifier so the amplitude goes past some sort of minimum and maximum (such as +/-1.0), then running the result through a cosine function.

If, instead of running the signal through a cosine function, you run it through a hyperbolic tangent function, you get a soft clipping waveshaper, which is a pretty good approximation of overdrive.

You can see the cosine and hyperbolic tangent examples in the screenshot.

You can use many mathematical functions to create various interesting waveshapers. Hard clipping can be done with a mathematical function with a condititional, like "If n is greater than 1.0, then return 1.0. If n is less than -1.0, then return -1.0. Otherwise return n".

Wavetables can be used as waveshapers, by using the wavetable as a lookup table by amplitude. This is how the WMD Geiger counter waveshaper works (although it also has a bitcrusher, filter, and distortion circuit). The Wiard Waveform City can be used as a wavetable oscillator or waveshaper.

I wrote a wavetable-based waveshaper that runs on a Maple, which is like an Arduino. It should run with little or no modification on any Arduino-compatible device which has a DAC and is fast enough.
very Interesting. Highly aprreciate your explanations. Kind regards !
Great stuff on this thread! Must try some of the above with a ‘scope hooked up so I can see. Will start with the “S&H subtraction” formula. So cool!
Rex Coil 7
Devilwidget wrote:
...What are wavefolder doing that a rectifer is not to add multiple folds?
The wavefolder adds gain to the output. The diodes suck a lot of gain from the input signals. Most wavefolders also provide convenient inputs for voltage control of various functions.

But reduced to the salt, the powered wave folder is providing "make up gain" to the output. Pretty much like the powered ring modulators ... there are gain stages added to boost the output since the diode ring sucks so much voltage out of the signal.

Unless you build either the wavefolder or the ring modulator using LEDs as diodes. With LEDs there is FAR less gain reduction.

My suspicion is that it will be difficult or impossible to simulate wavefolding with other modules, but certainly there are dozens of ways of waveshaping which will yield interesting results.

The ufold demo video on this page is how I understood what wavefolding does.

I did forget to mention that there are other wavefolding techniques. IIRC the Topobrillo Triple Wave Folder can do more of a "hard reflection" style vs. the ufold's softer approach where the wave seems to curl in on itself.
Maybe not folding but you get the idea hopefully, in this he morphs waveforms without wavetable synths..
Interpolating scanner; input audio into the control input, positive offset into the even-numbered inputs, negative into the odd-numbered.
Alex January
You can make a primitive kind of wavefolder with two "east coast" oscs by phase-syncing and frequency-modulating the 1st osc with the square output of the 2nd osc, while sending the same 1v/o signal to both. Listen to the sine from the 1st osc (and check it on an oscilloscope): it'll be wavefolded! You'll then be able to set the harmonics symmetry (ie. which overtone frequencies are highlighted) by changing the pitch of that osc and you'll control the harmonics order (ie. multiply your overtones) by setting the fm ratio (at least until 12 o'clock, past that you are in pure FM territory), and also a little bit by modulating the pulse width of the 2nd osc. Send the sine waves from both oscs into a mixer and you'll have a timbre control, going from pure sine to wavefolded sine. Patch your fm modulation through a vca and you'll be able to automate your wavefolding modulation.
luketeaford wrote:
If I am not mistaken, he gives a few clues in this talk: waveshaping is always dependent on amplitude and it works somehow by FM of 0 pitch which goes way beyond my understanding of how or what that means.

That's on the right track. I've been playing with both wavefolding and phase modulation on the ER-301 thanks to a couple of helpful things I found online: d-Serge-and-Lockhart-R-L-75-kO-wavefolder-models_fig3_321985944

For basic wavefolding: map the input onto a sine function. Amplify the input to increase the amount it gets folded.

(For subjectively nicer wavefolding, the transfer function in that second link is what a single stage of the middle section of the Serge Triple Waveshaper does. Run the output of that stage into another stage, as many times as necessary... but honestly, one or two already sounds pretty good.)

For phase modulation, you mix two signals and map the result onto a sine function, just don't crank the gain as you do in wavefolding.

This is pretty much how FM Aid works as well as the Sinulator, and the Yamaha DX series (digital sawtooth oscillators mixed and fed into sine lookup tables).

You should be able to use a triangle-to-sine shaper, Geiger Counter or Megawave, Piston Honda external input, etc. Or a VCO that can drop to LFO rate but does thru-zeru linear FM -- like the E370 for instance. It's not perfect but it gives kind of a cool character.
Here's an example of doing this with the E370. It's intensely FMing a slow LFO-rate sine. You could also phase modulate rather than using FM, but the phase modulation range is more limited than TZFM on the E370.

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