On Sun, 11 Dec 2005 22:37:05 +0100 Atte Andr? Jensen <atte.jensen@xxxxxxxxx> wrote: > Hi > > Suppose I have an A with a frequency of 440 hz. Which formula should I > use for transposing x semitones up/down? So which frequency would the Bb > a half step higher for instance have? What about cents (1/100's of half > steps)? One half step in equal tempered tuning is the frequency ratio of 1:2^(1/12) a.k.a the twelfth root of two. So, for an octave you get: 1:(2^(1/12) * 2^(1/12) * .... * 2^(1/12)) = 1:(2^(1/12))^12 = 1:2 :) And for any interval of n semitones you get a frequency ratio of: 1:(2^(1/12))^n = 1:2^(n/12) Sorry, i don't know about cents. It might be the 100th root of 2^(1/12) a.k.a 1:(2^(1/12))^(1/100) = 1:2^(1/1200). So when you go 1200 cents (1:2^(1200/1200) = 1:2) you have again the octave. No guarantee on that though. Regards, Flo -- Palimm Palimm! http://tapas.affenbande.org
