Pure tone

Pure tone

A pure tone is a tone with a sinusoidal waveshape.

A sine wave is characterized by its frequency — the number of cycles per second, or its wavelength — the distance the waveform travels through its medium within a period, and the amplitude — the size of each cycle. A pure tone has the unique property that its waveshape and sound are changed only in amplitude and phase by linear acoustic systems.

History

A pure sine wave is an artificial sound. That means that although some natural sounds may resemble it (i.e. the chirp of some birds and so presumably of some dinosaurs) a pure sinewave had never been heard until it was created by man. The credit to the first creator of and a sinewave likely goes to Helmholtz for his creation of the 'Helmholtz siren', a mechanical device that sends compressed the air through holes in a rotating plate. This is presumably the closest thing to a sign wave that was heard before the invention of electronic oscillators.

Acoustic properties

Sinewaves are generally uncomfortable to the ear, and are more damaging to the ear than other noises at equal volumes. Sinewaves are often more difficult than other sounds at placing the location of its source- they seem to ‘fill the room’.

Fourier theorem

The Fourier theorem states that any periodic waveform can be approximated as closely as desired as the sum of a series of sine waves with frequencies in a harmonic series and at specific phase relationships to each other.

The lowest of these frequencies (the fundamental frequency), which is also the inverse of the period of the waveform, determines the pitch of the tone, which is perceived by the human hearing. In music, notes are assigned to tones with different fundamental frequencies, in order to describe the pitch of played tones.

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