Musical sounds, musical instruments and musical signals

The physics of musical instruments underlies the sounds and signals they make. The nature of musical sounds is described, at a simple level, in a chaper I wrote (Wolfe, J. (2012) "Musical sounds and musical signals" in Sound Musicianship: Understanding the Crafts of Music. A. Brown (ed.) ISBN 13: 978-1-4438-3912-9 . ). Limited to print, that chapter contains no sound examples, film clips or animations. Further, because of the breadth of the topic and the limited length of the chapter, its treatment of each topic is brief. I therefore anticipated that many readers would seek more information. Hence this site: a multimedia appendix to that chapter.

picture of a Chladni pattern of a violin back

This appendix provides a small number of sound files or animations that illustrate the topics raised in the chapter. In each case, it also has links that give further explanation, sound files, film clips or animations. It uses two resources written by the same author: Physclips is a multi-level, multimedia introduction to physics, of which Volume II concerns Waves and Sound. A large web site, Music Acoustics is maintained by the author's research lab, which gives introductions to the acoustics of musical instruments, including the voice.


Sound, vibrations and resonance

Frequency and pitch

Rhythm, time and frequency; muscles, nerves and hearing

Intensity, pressure and loudness

Pure tones, harmonics, periodic and non-periodic sounds; Timbre, spectrum, envelope and transients

The first six harmonics of a sawtooth wave, sounded one at a time.

Harmony, scales and temperaments

Music as a signal


An overview of musical instruments

DC-AC conversion

    animation of stick-slip motion

    Bowed strings, wind instruments and the voice can produce steady sustained tones, because they can convert a steady ('DC') supply of energy from the arms or breath into that of oscillatory ('AC') motion. This observation is of fundamental importance in music acoustics because it gives rise to harmonic spectra and thus to harmony. Nearly harmonic spectra can be produced by plucked and struck strings, but this is, comparatively, a very recent invention.

    The animation at right shows how a bow, travelling with a steady speed (DC), excites a vibration (AC) in a string. (From Bows and strings.) The lateral force between bow and string is related to their relative speed and other variables by equations that are nonlinear: the force is not proportional to the speed (or position).

    Similarly, the relations between the vibration of a brass player's lips, a woodwind reed, a flute's air jet or a singer's vocal folds and the air flow past or through them are nonlinear (meaning that the change in air flow is not proportional to the change in the other variable).

    Without going into mathematical details, we note that this nonlinearity has the effect of producing periodic vibration with high harmonics, and the presence of harmonics has the important musical consequences noted above.

    The graph below is a schematic of air flow vs time past a vibrating reed for successively higher dynamic levels. Vibration up and down the bold line converts DC flow into AC flow in reed instruments. More details at Introduction to clarinet acoustics.

clarinet reed schematic

Strings

Wind

Impedance matching: getting sound power out

Voice

More resources

© 2011, JoeWolfe

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