Wavefolder

1. Fold Knob Sets the input signal gain to adjust the amount of folding. Folding thresholds are +5V and -5V.
2. Topology Selector Switches between parallel, series and digital topologies.
3. Bias Knob Applies a bias to the input signal, changing the symmetry of the folding to affect the harmonic content.
4. Smooth Knob Adjusts the amount signal smoothing. Effect depends on the topology.
5. High Quality Switch Enables or disables oversampling.
6. AC Coupling Switch Enables or disables a DC-blocking filter at the output.
7. Inputs Signal to be folded (stereo), with input level trim knob.
8. Outputs Folded signal (stereo), with output level trim knob.

Overview ⚓︎

A staple of so-called west coast synthesis, wavefolding is an effect that modifies a signal by folding it when it crosses a certain threshold. By applying a gain to the input signal with the Fold knob, the number of folds applied to the signal can be adjusted.

The following figure illustrates the effect of the Wavefolder on a triangular wave when the Fold knob is set to 4× gain.

In this module, the positive and negative folding points are approximately +5V and -5V; this can vary slightly depending on the chosen topology.

To see the Wavefolder module in action with an oscilloscope, choose All Patches in the Patches Library and open the Basics—Demo: Audio Shapers patch.

Usage ⚓︎

Patch the module’s input and output into an audio signal path. Turn the Fold knob to adjust the amount of folding, or modulate it with a LFO or envelope for constant spectral variations.

Since wavefolding adds harmonics to an existing signal, it works best on simple waveforms like sine or trangular waves. It can also work on sawtooth, or as a heavy distortion effect on any complex audio signal. However, it will not work well on square or pulse waves, since there is no slope to fold on these waveforms.

Different tones can be obtained using the Topology switch, the Bias knob and the Smooth knob. These are described in depth below.

Wavefolding can cause aliasing to occur, which is heard as dissonant frequencies added to the signal. This is especially obvious with high amounts of folding on sounds playing in the upper octaves. The High Quality (HQ) switch enables oversampling to reduce the amount of aliasing in the audible frequency range and round out the sound. This is enabled by default when adding the module to a patch.

In Depth ⚓︎

Wavefolder Topology ⚓︎

Wavefolding can be achieved in different ways in the analog and digital worlds. Use the Topology switch to choose between these three different topologies:

• Parallel: Inspired by synth pioneer Don Buchla’s classic design, this topology mixes the input signal with five special folding circuits to produce up to five folds in the signal.

• Series: This is an emulation of a typical analog serial wavefolder, where the input signal passes through six successive folding circuits.

• Digital: Mathematically perfect wavefolding. There is no limit on the number of folds applied to the signal.

The parallel and series folders simulate analog circuits, so their folding threshold varies slightly for each folding stage. Also, because they both have a fixed number of folding circuits, there is a point past which the Fold knob will increase the signal’s voltage beyond +5V or -5V, but no more folding will occur. When this happens, a smooth saturation applied to the output prevents the signal from getting too loud.

Because the digital topology can have any number of folds, it can be more prone to aliasing. When using it, make sure the HQ (high quality) feature is enabled and avoid extreme folding on high-frequency sounds.

Bias ⚓︎

The Bias knob applies a negative or positive voltage offset to the input signal. This changes the symmetry of the wavefolder, affecting the timbre of the folding effect.

The following figure shows the effect of 4× wavefolding on a triangular wave with +2.5V bias:

Compare this to the previous figure showing the same effect without bias; we see that with bias, the middle part goes beyond 0V. The difference may look subtle, but the sound is quite different.

Adding bias may introduce a DC component to the output signal, which can cause problems further down the signal path. The AC switch activates an internal DC-blocking filter that removes this DC component. We recommend leaving this feature enabled unless the module is used to process CV signals.

Smooth ⚓︎

Wavefolding can sound harsh, especially at high Fold gains or when applied to a harmonically rich signal. As its name implies, the Smooth knob can smooth-out the wavefolding effect.

• For the parallel topology, it controls a first-order low-pass filter applied to the output.

• For the digital topology, it controls a soft-clipping saturation that gradually rounds the folding corners.

• For the series topology, it does a bit of both.

Gain Staging ⚓︎

The folding thresholds of +5V and -5V were chosen so that the Wavefolder works as expected on raw oscillator signals. When using it elsewhere in the signal path, you may want to adjust the input level so that the signal isn’t folded when the Fold knob is at 1× gain. Simply follow this procedure:

1. Double-click on the Fold knob to set it to 1x gain.
2. Adjust the input level with the input trim knob until the fold LEDs turns on.
3. Dial back the input level so that the fold LEDs remain off.
4. Adjust the output level to compensate for the input gain. For example, if the input gain is at -6 dB, set the output gain to +6 dB.

Folding CV Signals ⚓︎

The Wavefolder module can be used to transform CV signals, although it is better suited for audio signals. With CV signals, always disable the high quality (HQ) mode and AC coupling.

Unless you really need features that are specific to this module, it’s probably better to use the CV Shaper which provides two folding modes, is optimized for CV signals, and can work with unipolar envelopes.

Using the Wavefolder as a VCA ⚓︎

When the Fold knob is turned fully counterclockwise, the gain goes down to 0× and the audio output is turned completely off.

By applying an envelope like the ADSR to one of the Fold knob’s modulation input, the Wavefolder can be used as a VCA that can both control the volume and the timbre of the sound. A simple bass or lead patch with lots of character can quickly be whipped up with a sine oscillator, an ADSR and a Wavefolder.