The logarithmic relation of sound frequencies used in most modern Western music. The frequency of each higher octave is twice the preceding one, i.e., an octave is a frequency ratio of 2:1. An octave band consists of all the frequencies within an octave. There is one octave between 100Hz and 200Hz, also between 1kHz and 2kHz. Octaves are perceived as equal pitch intervals, even though the true bandwidth in Hertz varies with the frequency level of the octave. The name arises from the musical practice of defining the eight notes of the scale within a doubling of the frequency. To ears, two frequencies an octave apart sound like the same note.

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