# Fmod change speed by pitch and pitch shifter

i have a requirement: changing the speed of the event.
first, i use pitch to change speed, but the pitch of audio changed.
so, i use pitch shifter to adjust pitch.
the question is, i do not know the scale factor between them.
for example:
case1: if the speed of voice is 2, what values shall i assign pitch and pitch shift respectively.
case2: if the speed of voice is 0.5, what values shall i assign pitch and pitch shift respectively.
is there is an accurate relationship between the speed, pitch, and pitch shifter.
can you give me a math formula.

The speed of an event is doubled/halved for each octave/12 semitones - so, for example increasing the pitch of an event by 12st is the same as doubling its speed, and decreasing the pitch by -12st is the same as halving its speed.

The resulting formula is as follows:

`speed = 2.0^(semitones/12.0)`

Where `semitones` is the amount of semitones to shift in pitch, and `speed` the equivalent change in speed.

thanks for your reply, it clearly expained the relationship between speed and the pitch.
i also want to kown how much pitch shifter will be assigned to make sure the pitch is not changed.
for example, do you mean if i change the speed to 2, i should assign pitch to 12, and pitch shifter to -12 to make sure the audio pitch is not changed.

If you want to keep the pitch the same while slowing down the audio, then you’ll want to use the inverse adjustment - i.e. if you set the pitch shifter to x2.0, you should set the event pitch to -12st.

the range of pitch in pitch shifter is 0.5~2, i can not twist the value to -12 if the speed is x2.0.

If you want to halve the speed of the audio but keep the pitch the same, you need to set the event pitch to -12st, and the Pitch Shifter pitch to 2.00x:

The opposite, with event pitch at +12st, and Pitch Shifter pitch at 0.50x, will double the speed of the audio while keeping the pitch the same:

i know the relationship between speed and semitone is:
speed = 2.0^(semitones/12.0)
i understand the cases you gave me. 2 speed, 12 pitch, and pitch shifter is 0.5;
and 0.5 speed, -12 pitch, and pitch shifter is 2.
but if i want to change speed to 1.5, or any other value, i can calculate the pitch value bu formular above, but i do not know what is formular between speed and pitch shifter. meanwhile, i also observed that the range for pitch shifter is 0.5~2.
can i you tell me the formular between speed and pitch shifter, because any speed from 0.5 to 2 we could assign.

Apologies - I may have been unclear before, so please correct me if I’m misunderstanding you now.

Do you specifically want the inverse formulas between the pitch shifter’s pitch (0.5 to 2.0), and event pitch (-24st to 24st)? In that case, assuming `eP = event pitch` and `sP = pitch shifter pitch`, they are:

`sP = 2^(-eP/12)`

and

`eP = -12*log2(sP)`