Editing Octave (section)

==Explanation and definition==
An octave is the [[interval (music)|interval]] between one musical [[Pitch (music)|pitch]] and another with double or half its [[audio frequency|frequency]]. For example, if one note has a frequency of 440&nbsp;[[Hertz|Hz]], the note one octave above is at 880&nbsp;Hz, and the note one octave below is at 220&nbsp;Hz. The ratio of frequencies of two notes an octave apart is therefore 2:1. Further octaves of a note occur at <math>2^n</math> times the frequency of that note (where ''n'' is an integer), such as 2, 4, 8, 16, etc. and the reciprocal of that series. For example, 55&nbsp;Hz and 440&nbsp;Hz are one and two octaves away from 110&nbsp;Hz because they are {{Frac||1|2}} (or <math>2^{-1}</math>) and 4 (or <math>2^{2}</math>) times the frequency, respectively.

The number of octaves between two frequencies is given by the formula: <math>\text{Number of octaves} = \log_2\left(\frac{f_2}{f_1}\right)</math>

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File:Middle_C,_or_262_hertz,_on_a_virtual_oscilloscope.png|[[Oscilloscope|Oscillogram]] of [[C (musical note)|middle C]] (261.62&nbsp;Hz) (scale: 1 square is equal to 1 [[millisecond]])
File:C5_523_Hz_oscillogram.png|C<sub>5</sub>, an octave above middle C. The frequency is twice that of middle C (523.25&nbsp;Hz).
File:C3_131_Hz_oscillogram.png|C<sub>3</sub>, an octave below middle C. The frequency is half that of middle C (130.81&nbsp;Hz).
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