Scientific pitch notation creates a linear pitch space in which an octave spans 12 semitones, where each semitone is the distance between adjacent keys of the piano keyboard. Distance in this space corresponds to musical pitch distance in an equal-tempered scale; 2 semitones being a whole step, 1 semitone being a half step. An equal-tempered semitone can also be subdivided further into 100 cents. Each cent is semitone or octave. This measure of pitch allows the expression of "microtones" not found on standard piano keyboards. The notation is sometimes used in the context of meantone temperament, and does not always assume equal temperament
Octave an octave apart is therefore 2:1. Further octaves of a note occur at formula_1 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 Hz and 440 Hz are one and two octaves away from 110 Hz because they are (or formula_2) and 4 (or formula_3) times the frequency, respectively. The number of octaves between two frequencies is given by the formula: The octave is defined by ANSI as the unit of frequency level when the base of the logarithm is two. After