Twelfth root of two
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The twelfth root of two or 12√ is an algebraic irrational number. It is most important in music theory, where it represents the frequency ratio of a semitone in twelve-tone equal temperament. Historically this number was proposed for the first time in relationship to musical tuning in 1580 (drafted, rewritten 1610) by Simon Stevin.
The twelfth root of two to 20 significant figures is 1.0594630943592952646. Fraction approximations in order of accuracy are 18⁄17, 196⁄185, and 18904⁄17843.
The equal-tempered chromatic scale
(to six places)
|B||493.88||2 2⁄12||1.122462||~ 9⁄8|
|C♯/D♭||554.37||2 4⁄12||1.259921||~ 5⁄4|
|D||587.33||2 5⁄12||1.334839||~ 4⁄3|
|E||659.26||2 7⁄12||1.498307||~ 3⁄2|
|F♯/G♭||739.99||2 9⁄12||1.681792||~ 5⁄3|
The final A (880 Hz) is twice the frequency of the lower A (440 Hz), that is, one octave higher.
Since the frequency ratio of a semitone is close to 106%, increasing or decreasing the playback speed of a recording by 6% will shift the pitch up or down by about one semitone, or "half-step". Upscale reel-to-reel magnetic tape recorders typically have pitch adjustments of up to ±6%, generally used to match the playback or recording pitch to other music sources having slightly different tunings (or possibly recorded on equipment that was not running at quite the right speed). Modern recording studios utilize digital pitch shifting to achieve similar results, (although the "beat" is not affected—the moment-to-moment frequency is sampled, then altered; this allows the tempo to remain unchanged) ranging from cents up to several half-steps.
DJ turntables can have an adjustment up to ±20%, but this is more often used for beat synchronization between songs than for pitch adjustment, which is mostly useful only in transitions between beatless and ambient parts. For beatmatching music of high melodic content the DJ would primarily try to look for songs that sound harmonic together when set to equal tempo.
- Just intonation § Practical difficulties
- Music and mathematics
- Piano key frequencies
- Scientific pitch notation
- The Well-Tempered Clavier
- Musical tuning
- Nth root
- Barbour, J. M. (1933). "A Sixteenth Century Approximation for π". American Mathematical Monthly. 40 (2): 69–73. JSTOR 2300937.
- Ellis, Alexander; Helmholtz, Hermann (1954). On the Sensations of Tone. Dover Publications. ISBN 0-486-60753-4.
- Partch, Harry (1974). Genesis of a Music. Da Capo Press. ISBN 0-306-80106-X.