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FM Brass

Jean-Claude Risset observed (1964-1969), based on spectrum analysis of brass tones [233], 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[40]). 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.G.6 above. Note how the FM index is proportional to the amplitude envelope (carrier amplitude).

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FM Harmonic Amplitudes (Bessel Functions)