Musical Acoustics

What is the difference between pitch and frequency?

Boston Symphony Hall, designed by physicist Wallace Clement Sabine (1868–1919), is the first concert hall designed specifically to enhance the sound of an orchestra. Sabine, who designed the hall in the late 1890s, discovered the relationship between sound intensity, absorption, and reverberation time. Sound reflections can either enhance or ruin a sound. Sabine discovered that having strong reflections immediately after a sound was produced would enhance the acoustics, but if sound was reflected midway between the source and the listener it would detract from the acoustics because the time of travel would be significantly different.

Sabine’s Boston Symphony Hall, built in 1900, established an excellent reputation for sound quality, mostly due to the choices of sound absorption materials as well as the strategic placement of reflecting material. The goal was to use the sound reflecting materials (high percent reflection ratios) to create strong initial reflections, while using sound absorbing materials (low percent reflection ratios) to absorb most of the energy from sound that would ordinarily reflect off of the high ceiling and the side walls in the rear of the hall.

Frequency, like sound intensity, is a physical property. Pitch, like loudness, is a description of how the ear and brain interpret the sound. Pitch is primarily dependent on frequency, but depends somewhat on loudness, timbre, and envelope, which will be discussed below. Humans hear pitch in terms of the ratio of two tones. The ear perceives two notes to be equally spaced if the they are related by a multiplicative factor. For example, the frequency of corresponding notes of adjacent octaves differ by a factor of 2. Notes in common chords are related by ratios of 3:2, 4:3, 5:4, etc. In the same way, the perceived difference in pitch between 100 hertz and 150 hertz is the same as between 1,000 hertz and 1,500 hertz.


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