Combination tones and multiphonics in a physics of music lab

Abstract

Laboratory exercises related to multiphonic tones in wind instruments have been developed for use in an undergraduate Physics of Music class. Although the concepts of nonlinear mixing and production of combination tones can be challenging to present at a non-technical level, a hand’s-on (mouth’s-on!) approach allows students to can gain a visceral and aural appreciation of this type of mixing and its musical use by wind players. The exercises make use of inexpensive free-reed pitch pipes. A pair of pipes can be played independently, producing a linear combination of the two sources, and as a pair of coupled nonlinear oscillators, resulting in combination tones. The differences between the two types of mixing are heard and viewed on a spectrogram in real time. Unlike multiphonics produced by advanced woodwind and brass players, every student can produce these combination tones with pitch pipes. Most can also sing a fixed pitch while playing a pipe to achieve another multiphonic effect. The exercises are readily extended to harmonicas, as available, where difference tones are often heard quite clearly, and the nonlinear mixing forms an essential part of the instrument’s timbre. Additional multiphonic examples are also illustrated.