Frequency and Pitch

A discussion of audio tones in the physics classroom will include mention of their frequency. The frequency of a periodic signal is a well-defined quantity that can readily be measured. A concept related to frequency is that of pitch. Pitch is a perceived quantity that cannot be measured directly and is most important when listeners characterize periodic acoustic signals. The distinction between frequency and pitch is often simplified or even overlooked entirely. Several examples are presented here that clearly illustrate that pitch and frequency are not always simply related. The scientific study of frequency and pitch dates back to at least the time of the Pythagoreans,1,2 though the distinction between frequency and pitch may not have been considered until much later. In the 19th century, after the Fourier series was introduced, well-known physicists such as Helmholtz, Ohm, and Seebeck spent some effort considering the connection between the components of acoustic spectra and pitch.3 With the development of computer-generated sounds starting in the 1950s, a more detailed study of pitch perception has become possible. Now, with the use of readily available and inexpensive audio editing software, many of these same ideas are easily explored in the physics classroom and/or may be suitable for student project-based work