AUD · Audio tools

Wavefolder

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Often followed by + Filter + Limiter + Gain

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Fold a waveform

A wavefolder is the timbre control on a west coast synth voice, where harmonics are added by reflecting the waveform rather than by filtering a rich one down. Feed it a sine and it turns into something closer to a square through a series of folds; feed it a full mix and it turns into grit that follows the music’s dynamics.

Fold sets how hard the signal is driven into the folding curve, from an exact passthrough at 0 to about twelve folds of a full scale peak at 100.

Folding against clipping

Clipping and folding both start at the same place, when the signal exceeds what the curve can pass. What happens next is different. A clipper holds the output at its limit for as long as the input stays over it, so the waveform gains flat tops and the harmonics it adds stop growing once it is well past the knee.

A folder sends the excess back down. A peak that goes 2.4 times past the threshold comes out at a completely different point than one that goes 2.0 times past it, so the timbre keeps changing with amplitude long after a clipper would have stopped responding. That is why a folder tracks an envelope and a distortion pedal does not.

Symmetry

Symmetry adds a fixed offset before the fold, up to 0.9 of full scale in either direction. Centred, the curve treats both halves of the waveform identically and only odd harmonics appear, which is the hollow sound of a symmetric folder. Offset, the two halves fold at different amplitudes and even harmonics arrive with them, which fills the sound out.

The fold keeps most of that offset in its output, so a 12 Hz high pass removes it afterwards. Without it a strong Symmetry setting would reach the file as a waveform sitting off centre with no headroom on one side.

Stages and the two curves

The fold depth is divided across the cascade rather than repeated, so the same Fold setting means the same total gain at one, two or three stages. What changes is the route: three gentle folds applied one after another produce a denser series than one hard fold of the same depth, because each stage is folding a waveform that already has folds in it.

Sine and Triangle are the two curves. The sine folder rounds each reflection, which keeps the higher harmonics softer and is what most analogue folders approximate. The triangle folder reflects with a hard corner at each fold, which adds a brighter and more brittle series. Both reduce to a straight line at Fold 0.

Aliasing

A folder is the worst case for aliasing in a browser: one fold of a sine already carries harmonics past the 30th, and applied at the file’s own sample rate they reflect around Nyquist and land as tones unrelated to the note. The curve therefore runs at eight times the sample rate through the shared oversampler, and the extra harmonics are filtered off before the signal comes back down. That costs 16 samples of latency, which is declared to the runtime so the dry path is aligned and the export is trimmed.

Where it fits

On a synth line or a bass, before the filter, which is how the technique works on a real voice: fold to add harmonics, then filter to shape what the fold made. On a full mix, keep Fold under 30 and Mix under 50%, since a folder applied to a dense source stops sounding like harmonics and starts sounding like a fault.

Frequently Asked Questions

A clipper flattens everything past its threshold, so the waveform stops changing shape once it is well past the knee and the harmonics settle into a fixed pattern. A folder reflects the excess back down instead, so a peak that goes twice as far past the threshold comes out somewhere else entirely and the harmonic series keeps moving as the note decays.

Foldback there is one triangle fold with its level normalised. Here the fold is cascaded up to three times, so each stage folds what the last one already folded, and Symmetry offsets the waveform before it reaches the folder so the two halves are treated differently. Neither is reachable by turning the distortion up.

It moves the waveform off centre before folding, which makes the folder treat the positive and negative halves differently. A symmetric folder produces odd harmonics only; an asymmetric one adds even harmonics, which sounds fuller and less hollow. The offset the fold leaves behind is removed afterwards with a 12 Hz high pass.

The number of folds follows the signal's amplitude, so a loud attack folds several times and the decay folds fewer and fewer. That is the character of the effect rather than a side effect. The file's overall level is taken out by a slow envelope first, so a quiet recording folds the same as a loud one while the playing dynamics still come through.

The same fold depth is split across the cascade. One stage folds once, hard. Three stages fold a signal that has already been folded twice, which gives a denser and less regular harmonic series at the same setting. On a simple waveform the difference is obvious; on a full mix it mostly reads as more or less grit.

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