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Acoustics - Definitions

A musical note is the result of successive similar disturbances in the air, provided that they follow each other at regular intervals with sufficient rapidity. Similar disturbances following each other at regular equal intervals are said to be periodic. The interval of time between successive impulses of a periodic disturbance determines the pitch of the note produced - that is, its position in the musical scale. The pitch of a note is therefore generally expressed by the number of periodic disturbances per second required to produce it. This number is called the 'vibration number,' or 'frequency' of the note.

It generally happens that any apparatus for producing a note of given frequency produces at the same time notes of other frequencies. The result is a complex sound, equivalent to the combination of a series of simple sounds or tones. The simple tones of which the complex sound may be regarded as consisting are called 'partial tones;' the gravest of these - that is, the one of lowest pitch - is called the 'fundamental tone' of the sounding body, and the others are called 'upper partials.' A note which has no upper partials is called a pure tone. By means of suitable resonators the different partial tones of a complex note may be made very clearly audible. For many musical instruments, as organ-pipes, string instruments, &c., the ratio of the vibration frequency of any upper partial tone to that of the fundamental tone is a simple integer, and the upper partials are then called 'harmonics;' for others, again, as for bells, tuning-forks, &c., the ratios are not integral, and the upper partials are said to be inharmonic.

Last Update: 2011-03-19