# Looking for a formula...

DSP, Plug-in and Host development discussion.
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spaceman
KVRAF
8958 posts since 9 Jan, 2004 from leroyaumeuni
Rozzer wrote:
Big Tick wrote:
Rozzer wrote: To change bpm X to bpm Y, I'd have to pitch-shift by Z semitones.
If I have X & Y, how can I calculate Z ?
Should be something like:
Z = 12 * ln(Y/X)/ln(2)

So if you double the bpm, you're pitch-shifting by 12 semitones. ln is neperian log, btw.
'Tick
Thanks BigTick - I think that's what I'm looking for

useless bunch he said

My other host is Bruce Forsyth

VicDiesel
KVRAF
2828 posts since 2 Mar, 2003 from The only civilized county in Texas
Rozzer wrote:To change bpm X to bpm Y, I'd have to pitch-shift by Z semitones.

If I have X & Y, how can I calculate Z ?
Every semi-tone up multiplies the frequency by the 12th-root of 2, call this "r". With the frequency the speed (in any measure) also goes up by a factor of r. Shifting n semitones then shifts by r^n.

So you're looking for the n that makes r^n = (Y/X). The answer to that is the log-base-r of Y/X. Your calculator doesn't have log-base-r, but the natural log ln, so that becomes n = log-r (Y/X) = ln (Y/X) / ln r.

I think.

EDIT this is the same as what Big Tick posted: ln r = (ln 2)/12, which makes it his formula.

V.

Rozzer
KVRian
Topic Starter
1120 posts since 4 Jun, 2003 from Skanky Manc
Brilliant - so if I wanted to reshuffle the formula so that I can know BPM Y after shifting BPM X by Z semitones, what would the formula be?

(god its been a long time since I did formulas)

cheers,
R zzer

CypherOne
KVRAF
7936 posts since 18 Feb, 2003 from out there somewhere
are you sure you're in the right job?...

Rozzer
KVRian
Topic Starter
1120 posts since 4 Jun, 2003 from Skanky Manc
CypherOne wrote:are you sure you're in the right job?...

shut it you

spaceman
KVRAF
8958 posts since 9 Jan, 2004 from leroyaumeuni
CypherOne wrote:are you sure you're in the right job?...

step by step.. year by year..

he'll get there

My other host is Bruce Forsyth

Big Tick
KVRAF
3387 posts since 29 May, 2001 from New York, NY
Y = X * exp(Z * ln(2)/12)

CypherOne
KVRAF
7936 posts since 18 Feb, 2003 from out there somewhere
Rozzer wrote:
CypherOne wrote:are you sure you're in the right job?...

shut it you
just kidding, Metal Mickey is fantastic (I never use it but hey...). Sorry kidding again, would I be right in thinking that MM features in Time Lapse?

Rozzer
KVRian
Topic Starter
1120 posts since 4 Jun, 2003 from Skanky Manc
Big Tick wrote:Y = X * exp(Z * ln(2)/12)
Ta muchly

Rozzer
KVRian
Topic Starter
1120 posts since 4 Jun, 2003 from Skanky Manc
CypherOne wrote:
Rozzer wrote:
CypherOne wrote:are you sure you're in the right job?...

shut it you
just kidding, Metal Mickey is fantastic (I never use it but hey...). Sorry kidding again, would I be right in thinking that MM features in Time Lapse?
I think Timelapse was pre-MM actually, but it does end up in most of my tunes

(i was only kidding too )

scuzzphut
KVRAF
3723 posts since 17 Apr, 2002 from Scotland
Kriminal wrote:1 semitone = 10BPM
I much prefer this method.

Rozzer
KVRian
Topic Starter
1120 posts since 4 Jun, 2003 from Skanky Manc
scuzzphut wrote:
Kriminal wrote:1 semitone = 10BPM
I much prefer this method.

Thanks again BigTick - those are working great

Paul_FX
KVRian
742 posts since 22 Jun, 2004
step by step.. year by year..

he'll get there
May be a long journey!

Paul
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FXpansion Audio UK Ltd