Working out BPM of a sample when changing the pitch

[1979.2]

Hi guys!

I would like some help. First off let me say I dont want to use timestretch. I want to do the maths!

I want to work out the BPM of a sample at 104 bpm when I reduce the pitch (of the sample) by say 4 octaves.

is there a formula?

thanks for your help


k

[zeoy]

I am using Tracktion and its auto tempo function has kept me off this kind of calculations but thinking that 1 octave down means half frequency I suppose this means double length. So after transposing n octaves down the new bpm should be (original bpm)/(2^n)=104/(2^4)=104/16=6.5 bpm in your example. That would be a killer dub loop

Someone correct me if that's nonsense ...

[1979.2]

thanks.

Is that 6.5 bpm off 104bpm. So the new tempo would be 97.50bpm?

[zeoy]

thanks.

Is that 6.5 bpm off 104bpm. So the new tempo would be 97.50bpm?

No, if you pitch down four octaves your new tempo will be 6.5 bpm . Four octaves its rather extreme. To put it simpler each time you pitch down one octave your bpms would be half of the original

[Breakpete]

Not 100% sure if this is going to be any help for you, but Mixmeister at www.mixmeister.com has a free bpm counter which is very accurate. Transpose your sample, export it and feed it into the bpm counter.

[1979.2]

ahh i see ! I didnt mean one octave then. whoops! I ment one semitone.

what would be the calculation now?

104bpm down 4 semitones.

[zeoy]

With semitones ther must be a 12 involved in the formula. I guess NewBPM=OriginalBPM/[2^(n/12)] where n=# of semitones you are transposing down ( the "^" symbol means ... to the power of ...). I will check it and report if the formula is wrong.

[zeoy]

I tested with 2 semitones and the formula seems right

For your example 104 bpm transposed 4 semitones down will be 82.54 bpm

[1979.2]

that works. wow complicated.
I'M still a little lost!

82.54=104/2^(.3)