Pure tone

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A pure tone's pressure waveform versus time looks like this; its frequency determines the x axis scale; its amplitude determines the y axis scale; and its phase determines the x origin.

A pure tone is a tone with a sinusoidal waveform; this is, a sine wave of any frequency, phase, and amplitude.[1]

A sine wave is characterized by its frequency, the number of cycles per second, its amplitude, the size of each cycle, and its phase that indicates the time alignment relative to a zero-time reference point. A pure tone has the property – unique among real-valued wave shapes – that its wave shape is unchanged by linear time-invariant systems; that is, only the phase and amplitude change between such a system's pure-tone input and its output.

Sine and cosine waves can be used as basic building blocks of more complex waves. A pure tone of any frequency and phase can be decomposed into, or built up from, a sine wave and a cosine wave of that frequency. As additional sine waves having different frequencies are combined, the waveform transforms from a sinusoidal shape into a more complex shape.

Sound localization is often more difficult with pure tones than with other sounds.[2][3]

See also[edit]


  1. ^ ANSI S1.1-1994 Acoustical Terminology
  2. ^ Stanley Smith Stevens and Edwin B. Newman (1936). "The localization of actual sources of sound". The American Journal of Psychology. 48 (2): 297–306.
  3. ^ Hartmann, W. M. (1983). "Localization of sound in rooms". The Journal of the Acoustical Society of America. 74 (5): 1380–1391. doi:10.1121/1.390163.