Wavefolding is a type of distortion synthesis where when the input amplitude exceeds the threshold, the peaks get cut off, similar to digital clipping. The difference is that in wavefolding, the curved amplitude peaks get inverted into a series of folds.
These folds produce complex spectra from simple waveforms so when you run a single sine wave through a wavefolder, very strange harmonics will emerge. Interestingly, saw and pulse waves may remain generally unaffected by wavefolding, but a mathematical explanation of this behavior is beyond the scope of this article.
Most wavefolders include an additional variable, sometimes called offset, that adds a positive or negative voltage bias. This offset shifts the center point of the input signal up or down. A positive offset will cause the positive sections of the signal to have higher amplitude while the negative sections will have less amplitude. Because of this, the user is able to apply more distortion to the positive signal than the negative signal, making this a non-linear distortion. In fact, with certain settings, you can even apply wavefolding to just the positive sections of the signal while leaving the negative sections unmodified or vice-versa.
The Intellijel uFold, pronounced “micro fold”, is a good example of a simple yet flexible wavefolding module. Turning the folds knob clockwise increases the input gain, causing more clipping and folding – essentially it is the distortion amount knob. When turning the symmetry knob from its center position, a positive or negative voltage offset amount is added to the signal. Make the following connections for one way to create a keyboard patch with a wavefolder:
- From the pitch output of a CV keyboard, such as a QuNexus, into a VCO’s 1V/Oct input
- From the keyboard’s gate output into an envelope generator’s gate input
- From the VCO’s sine wave output into a wavefolder’s audio input
- From the wavefolder output into a filter’s audio input
- From the filter’s audio output into the audio input of a VCA
- From the envelope generator’s output into the VCA’s CV input
- From the VCA’s audio output into your speakers
With this configuration you will already be able to use the uFold in many creative ways, but to truly unlock its potential you will want to patch a pair of control voltage sources into its folds and symmetry CV inputs. LFOs work well. Turn up the dedicated CV attenuators to control the depth of the modulation. One thing to keep in mind is that it possible for the control voltage to push the parameters into a zone where all audio output is silenced. If this occurs either dial back the CV attenuator or move the parameter knob closer to 12 o’clock.
Do yourself a favor and check out this cool demo video where you can see what happens when you apply audio rate modulation from a VCO into the CV inputs.