Wavetable Synthesis

For periodic sounds, the sinusoidal components are all harmonics of some fundamental frequency. If in addition they can be constrained to vary together in amplitude over time, then they can be implemented using a single wave table containing one period of the sound. Using interpolation (typically linear, but sometimes better), the table may be played back at any pitch, and its output is then multiplied by the amplitude envelope shared by all harmonics. (The harmonics may still have arbitrary relative levels.) This form of ``wavetable synthesis'' was commonly used in the early days of computer music.

In recent years, the term ``wavetable synthesis'' often refers to what was originally called sampling synthesis: playback of sampled tones from memory, with looping of the steady-state portion to create an arbitrarily long sustain [156,26,102,182]. In this book, we will use the original terminology. Hence, wavetable synthesis is defined as synthesis by looping through a stored period of a waveform, where the step-size through memory can be varied to produce different pitches. Amplitude shaping is handled by multiplying the output of the wavetable look-up by an amplitude-envelope generated separately. Because memory is now inexpensive, wavetable synthesizers are rarely used today, except in very low-cost environments such as cellular telephones. Most synthesizers today use ROM-based sampling synthesis (sample-playback synthesis) in conjunction with audio effects.

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About the Author: Julius Orion Smith III
Julius Smith's background is in electrical engineering (BS Rice 1975, PhD Stanford 1983). He is presently Professor of Music and Associate Professor (by courtesy) of Electrical Engineering at Stanford's Center for Computer Research in Music and Acoustics (CCRMA), teaching courses and pursuing research related to signal processing applied to music and audio systems. See http://ccrma.stanford.edu/~jos/ for details.