Brightness measures of trombone timbre
Trombone timbre is difficult to describe because of the multidimensional nature of timbre perception and because of inherent timbral variations with pitch and loudness. Following suggestions by Balzano (1986), a measure of trombone timbre is selected that is suited to the dynamic processes of trombone tone production. The measure is Scharfe (Aures, 1985), translated here as brightness, which is a weighted first moment of the spectral energy distribution. A descriptive study is undertaken to determine the usefulness of this measure, by testing its ability to discriminate between members of the trombone family (alto, tenor, and bass) and between performers using the same instrument.Systematic differences are found between instruments and between performers. For notes at the same loudness and pitch, alto trombone is brighter than tenor, which is brighter than bass. Differences between performers using the same instrument are smaller than differences between instruments. Differences between performers tend to be concentrated in regions of loudness and pitch. The regions are specific to the performers being compared and independent of instrument. Brightness of trombone tones depends primarily on loudness, and to a lesser extent on pitch. The rate of change of brightness with loudness depends on pitch and sounding length. Measured log brightness vs. log loudness and frequency can be approximated with a simple surface. It is concluded that brightness vs. loudness and pitch is a useful measure of trombone timbre. It yields results consistent with musical practice and musical understanding. Compared with verbal descriptions of timbre, its results are compact and reliable.
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