FM Brass

Jean-Claude Risset observed (1964-1969), based on spectrum analysis of brass tones [220], that the bandwidth of a brass instrument tone was roughly proportional to its overall amplitude. In other words, the spectrum brightened with amplitude. This observation inspired John Chowning's FM brass synthesis technique (starting in 1970[39]). For FM brass, the FM index is made proportional to carrier amplitude, thus yielding a dynamic brightness variation with amplitude that sounds consistently ``brassy''. A simple example of an FM brass instrument is shown in Fig.H.10. Note how the FM index is proportional to the amplitude envelope (carrier amplitude).

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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.