ASA 30 - Change In Timbre With Transposition

Description

High and low tones from a musical instrument normally do not have the same relative spectrum. A low tone on the piano typically contains little energy at the fundamental frequency and has most of its energy at higher harmonics. A high piano tone, however, typically has a strong fundamental and weaker overtones.

If a single tone from a musical instrument is spectrally analyzed and the resulting spectrum is used as a model for the other tones, one almost always obtains a series of tones that do not seem to come from that instrument. This is demonstrated with a recorded 3-octave diatonic scale played on a bassoon. A similar 3-octave "bassoon" scale is then synthesized by temporal stretching of the highest tone to obtain the proper pitch for each lower note on the scale. Segments of the steady-state portions are removed to retain the original note lengths. This way the spectra of all tones on the scale are identical except for a frequency scale factor. The listener will notice that, except for the highest note, the second scale does not sound as played on a bassoon.

References

J.Backus (1977), The Acoustical Foundations of Music, 2nd edition, (Norton &Co., New York).

P.R.Lehman (1962), The Harmonic Structure of the Tone of the Bassoon, (Ph.D. Dissertation, Univ. of Mich.).

Frequency
Time Delay

Transcript

A 3-octave scale on a bassoon is presented, followed by a 3-octave scale of notes that are simple transpositions of the instrument's highest tone. This is how the bassoon would sound if all its tones had the same relative spectrum.