James W. Beauchamp
School of Music, Univ. of Illinois, 2136 Music Bldg., 1114 W. Nevada, Urbana, IL 61801
Hong Kong Univ. of Science and Technology, Kowloon, Hong Kong
It is well known that spectral envelopes of brass tones vary with performed dynamic [D. Luce and M. Clark, J. Acoust. Soc. Am. 42, 1232--1243 (1967)]. In this study average spectral envelopes were computed as functions of normalized instantaneous rms amplitude using time-variant spectral data from a group of 15 trumpet swell tones with fundamental frequencies extending over a 2-octave range. It was found that 10 spectral envelopes, defined by amplitudes in each of 24 standard critical bands spanning the frequency range 0 to 10 000 Hz, were sufficient to characterize the tone set. Time-variant spectra were synthesized using the original rms amplitude-versus-time envelopes as driving functions to dynamically select and interpolate between the appropriate spectral envelopes for each moment of time. The time-variant spectra were then converted into sound signals using conventional additive synthesis. Since the synthetic tones sound almost identical to the originals, it appears that dynamic spectral envelopes are an important defining characteristic of trumpet tone behavior.