TimeStretch tempo formulas

[speedyrazor]

Hi, I am looking for the formulas for changing audio tempo. I have the one for going from 24fps to 25fps:

TimeStretch(tempo = 25.0/(24000.0/1001.0)*100.0)

What would be the correct ones for:

23.98 to 25
23.98 to 24
24 to 23.98
25 to 24
25 to 23.98

Kind regards.

[Selur]

It's always to/from to get a multiplier with base one and if your multiplier needs to have hundred as base you multiply the result by hundred like you do in your example,...
Not sure what you expected, but this seems to be basic math and you could simply replace your numbers in your example,...

[speedyrazor]

My math is not that good. Is this correct?:

23.98 to 25 - tempo = 25.0/(24000/1001)*100.0)
23.98 to 24 - tempo = 24.0/(24000/1001)*100.0)
24 to 23.98 - tempo = 23.976/(24000.0/1001.0)*100.0)
25 to 24 - tempo = 24.0/(25000.0/1001.0)*100.0)
25 to 23.98 - tempo = 23.976/(25000.0/1001.0)*100.0)

I am unsure of the 23.976 formular

[wonkey_monkey]

23.976 is a standard approximation for the correct "NTSC" film rate, which is accurately 24000/1001, so you're getting things a bit mixed up, I think.

Your initial piece of code is actually for 23.976 to 25, not 24 to 25. Sometimes people say 24fps when they really mean 23.976fps (and even then, they really mean 24000/1001 fps!)

The formula is: target_fps/source_fps*100.0

23.976 to 25 - tempo = 25.0/(24000/1001)*100.0
23.976 to 24 - tempo = 24.0/(24000/1001)*100.0
24 to 23.976 - tempo = (24000/1001)/24.0*100.0
25 to 24 - tempo = 24.0/25.0*100.0
25 to 23.976 - tempo = (24000/1001)/25.0*100.0

I think these are correct.

[creaothceann]

(24000 / 1001) / 24.0 * 100.0
(24000 / 1001) / 25.0 * 100.0

This will perform an integer divison first, so the result would be incorrect. Therefore:

(1.0 * 24000 / 1001) / 24 * 100
(1.0 * 24000 / 1001) / 25 * 100

[speedyrazor]

So ultimately it should be?

23.976 to 25 - tempo = 25.0/(24000/1001)*100.0
23.976 to 24 - tempo = 24.0/(24000/1001)*100.0
24 to 23.976 - tempo = (1.0*24000/1001)/24*100
25 to 24 - tempo = 24.0/25.0*100.0
25 to 23.976 - tempo = (1.0*24000/1001)/25*100

Just checking these are all correct?

[Groucho2004]

I would stick to the notation that is used in the documentation (and your first post), adding ".0" to all numbers.

[speedyrazor]

Adding the .0 made a lot of difference, they are now correct.
Thanks for the tip.