EXS 24 Logic Sampler Users Group

On a fine day, 24-04-2004, sam sutton wrote:

>Is there a ratio where cents or semi tone note changes on the EXS sample
>editor relate to BPM changes?
>
>For example if a sample is in 100BPM and I want to change it to 115BPM can I
>use the pitch change (+ 50cents?) as a formula to do this?

If you transpose a sample up one semitone, you multiply the frequency 
(or the bpm if you're concerned with loops) with 2^(1/12) (2 to the 
power 1/12) = 1.059463094
Since one cent is 1/100 of a semitone, tranposing up one cent means 
multiplying by 2^(1/1200) which is apporx. 1.00057779.

If your source bpm (or frequency) is src, and the destination bmp 
(frq) is dst, and you want to know how many cents you have to 
transpose the loop (sample) to get from src to dst, you're searching 
for the solution to this equation:
2^(x/1200) = dst/src.
The solution is:
x = 1200 * log(dst/src) / log(2)

If the log() you use is the base-10 log (as most calculators 
support), this can be simplified a little to
x = 3986.3137 * log(dst/src)

In your example: going from 100 bpm to 115 bpm means you want to 
multiply 100 by 1.15 (dst/src).  So the transposition you need is
1200 * log(1.15)/log(2) = 241.96 or 242.  That's 2 semitones plus 42 cents.

-- 
Hendrik Jan Veenstra   h @ k n o w a r e . n l
Omega Art: http://www.omega-art.com/