Wavetable synthesis

Wavetable synthesis is a sound synthesis technique that employs arbitrary periodic waveforms in the production of musical tones or notes. The technique was developed by Wolfgang Palm of PPG in the late 1970s and published in 1979, and has since been used as the primary synthesis method in synthesizers built by PPG and Waldorf Music and as an auxiliary synthesis method by Sequential Circuits, Ensoniq, Korg, Access and Dave Smith Instruments among others.

It was also independently developed by Michael Mcnabb in a similar time frame, and used in his classic work, "Dreamsong" (1977).

Principle

Wavetable synthesis is fundamentally based on periodic reproduction of an arbitrary, single-cycle waveform. In wavetable synthesis, some method is employed to vary or modulate the waveform definition or waveshape. With 1 degree of modulation, this waveform is one dimension of a two-dimensional array. Moving along the other dimension of the array selects different waveforms. A means of interpolating (by scaling and mixing) between adjacent waveforms allows for smooth transition from one selected waveform to the next. If adjacent waveforms contain subtly different harmonics (in magnitude and phase), the table can be swept, dynamically and smoothly changing the timbre of the tone produced. If the adjacent waves however, have radically different harmonic structures, an audible stepping will be heard and artifacts will be present due to the rapid change in harmonic content. Sweeping the wavetable is usually performed by use of an LFO or a ramp with the start position and direction of sweep being specified by the modulation parameters, and the LFO or ramp speed controlling the rate of the harmonic change.