Re: [sc-users] Playback rate to semitones

The midiratio solution is probably the easiest, and you'll get the freqs in tempered tuning.

Using Pythagorean ratios you wetting your feet in the 'just intonation' swampland, a lovely murky world with warm beating qualities. (https://en.wikipedia.org/wiki/Just_intonation).

With some caveats:

rate * (8/9) * (8/9) * (8/9) * (8/9) * (8/9) * (8/9) == 0.493

wheras:

rate * 1/2 == 0.5

also:

rate * (9/8) * (9/8) * (9/8) * (9/8) * (9/8) * (9/8) == 2.027

whereas:

rate * 2/1 == 2

So don't get dragged to far down by seconds if you want to stay true to to your root. ;-)

+Eirik

On Wed, Jan 9, 2019 at 5:26 PM <eli.fieldsteel@xxxxxxxxx> wrote:

You can use the midiratio method:

12.midiratio; //—> 2

The math involves multiplying the starting frequency by 2 raised to the power of n/12, where n is the up/down semitone shift.

Eli

On Wed, Jan 9, 2019 at 10:11 AM <kennethflak@xxxxxxxxxxxxxx> wrote:

Just got stumped trying to figure out a conversion between playback rate and semitones. Given that playing back a sample at a rate of 0.5 will transpose it down 12 semitones, and playing it back at 2 will transpose it up 12 st... How do I calculate arbitrary semitone transpositions up and down in terms of playback rates? My math part of the brain is apparently not working today.

Roosna & Flak - Contemporary Dance & Music
https://www.roosnaflak.com

--

_______________

Eli Fieldsteel, DMA

Director, University of Illinois Experimental Music Studios

Assistant Professor of Composition-Theory
Office: 217-300-0956
MB 4008, School of Music
1114 W Nevada Street

Urbana, IL 61801