Additive Synthesis Overview

Additive synthesis is a technique in which a signal is reconstructed from a summation of sinusoids and possibly other components. Each sinusoid has a time varying amplitude and phase:

where

and all quantities are real.

As mentioned previously, the sinusoidal signal model is efficient for tonal signals, such as voiced speech, steady-state wind instrument tones, plucked/struck strings, etc. It is inefficient for noise-like signals, such as unvoiced speech, and the ``chiff'' portion of flute/organ tones. It is also inefficient for attacks, (sharp time-domain transients) such as percussive note onsets.

An additive-synthesis oscillator-bank is shown in Fig.9.7, as it is often drawn in computer music [222,221]. Each sinusoidal oscillator [253] accepts an amplitude envelope (typically piecewise linear) and a frequency envelope , also typically provided as a piecewise linear function (in computer music). Also shown in Fig.9.7 is a filtered noise input, used in sines plus noise spectral modeling, to be discussed in §9.7.

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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.