«Wavolver II» waveshaper of Ian Fritz

The Wavolver is a versatile waveshaper that generates a special kind of double-pulse waveform along with an extra folded-wave section added between the pulses. It generates a wide range of timbres from a gentle sine or triangle wave to a very rich signal with multiple zero-crossings per cycle.

The circuitry works by only passing the input signal when its amplitude (positive or negative) is above a threshold set by the Pulse Width control. When it's below the threshold the output signal is zero, as shown on the left side of the following figure. The signal consists of steeple-shaped pulses that can be swept from narrow for high harmonic content to full width, which results in a triangle wave ("Width" and "Width mod" controls).

In addition to the double-pulse generator, the Wavolver has circuitry to generate a series of evolving folded waves between the pulses. These are mixed into the output via the "Fold mix" control. The right side of the above figure illustrates the folding at a 50% level for two different pulse widths. The folder output is available separately to allow individual processing of the double pulses and the folds.

In the Wavolver II there are several ways to modify the basic waveforms discussed above. First, the amplitude of the second pulse can be continuously tuned from -5V (as shown above) to +5V ("Pulse 2 amp" control). At full positive amplitude, the signal has two identical positive pulses, resulting in a signal at twice the frequency of the driving signal. Waves with the second harmonic stronger than the fundamental are musically useful, as some acoustic instruments (bowed strings) share this characteristic.

Another way to change the basic waveforms is to add a DC voltage offset to the input signal ("Offset" and "Offset mod" controls). A positive offset makes the first pulse stronger and wider and at the same time it makes the second pulse weaker and narrower. Again, this adds even harmonics into the output spectrum and results in some interesting timbres, especially when modulated. The graphic below illustrates these modifications.

Finally, the waveshape can be modulated by modulating the input waveform. There are many ways to do this, of course. As one example my SNICster module's output morphs continuously from Saw to Tri waveforms and produces a change in relative pulse position in the Wavolver's output (pulse position modulation).