tempo and tune relationship

What is the mathematical relationship between tempo and tune?
Example: I have a sample at 100bpm, I want to speed it up to 120bpm, only by using the tune (no time stretch).

Thxs

From http://www.ilio.com/spectrasonics/metamorphosis/linernotes.html:

tempo & pitch formula

the formula to determine how many cents you adjust to change loop tempos is:
Td = Desired tempo
Ts = Current Sample tempo
n = Detuning (in cents: 1200 cents = 1 octave, tempered scale)
n = ( 1200 / log[2] ) x log[Td / Ts]

Try entering it into a Scientific Calculator (like the one provided in Windows) like this:

Desired tempo / Current tempo = log * 1200 / 2 log = Detuning in Cents

Otherwise you could just do what stilo does and forget the maths.

I prefer the relationship between my ears and brain.

Thanks!
Exactly what I was looking for!!