EXS 24 Logic Sampler Users Group

EXS crew-
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?
Thanks,
Sam

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/

Hendrik Jan Veenstra wrote:
> 2^(1/12) (2 to the
> power 1/12) = 1.059463094
[etc...]

And if you just are like me, being too stupid to have a single clue about
such things (I still wonder how I can get away with my girlfriend who is
just making her diploma in maths and... uhm, theology ;o), you could simply
get one of the several calculators to do the maths for you. www.analogx.com
has one, www.wizoo.com as well I think (the latter should come as a Mac
version too).

Personally I recycle about all of my loops, so tempo calculations are a
thing of the past for me.

Regards,
Sascha

On Saturday, Apr 24, 2004, at 22:36 Pacific/Auckland, sam sutton wrote:

> EXS crew-
> 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?

I've written a utility "Kal-Q-Late" which does just that. It calculates 
pitch shift from a source and target tempo, and calculates a new tempo 
from a source tempo and pitch shift. It's available from the igMusic 
website. Navigate to:

http://www.igmusic.co.nz/features.html

and look for the link to "Kal-Q-Late". It's a 615k sit file for Mac 
OSX. I could probably port it to OS9 if there's enough interest.


    Ian

                     ------------------------------
                     Ian G. Morris   -   Tonewright
                          ian@...
                          www.igmusic.co.nz