In the vernacular of music, the pitch of a sound is completely determined by its frequency of vibration. Typical pitch standards in Western music assign a given frequency to one of the twelve notes in an octave: C, C#, D, D#, E, F, F#, G, G#, A, A#, B, and another symbol to indicate the relative position of the octave. For example, American Standard Pitch uses a subscript to indicate octave, and assigns to C4 (middle C) a frequency of 261.63 vibrations per second. Thus, a sound with the frequency 261.63 has the pitch C4 in American Standard Pitch. The pitch class of a sound is determined only by its note assignment and not by the octave in which the note occurs. Therefore, there are twelve pitch classes in Western music. C3 and C4 are in the same pitch class, but they have different pitches.
1
In acoustics, a sound is also quantified by its frequency of vibration. However, scientists refer to another quality of sound called pitch that is a subjective measure of the combination of the frequency and intensity of a sound. This is related to but distinctly different from the vernacular use of pitch in music. In acoustics, a unit of pitch called the mel (from melody) has a dependence on the frequency and the intensity at which a note is heard. For example, in acoustics, the note C4 heard with an intensity of 10-4 watts per meter2 has a different pitch than the note C4 heard with an intensity of 10-2 watts per meter2. In music, however, both of these sounds are considered to have the same pitch.
