# Tempo

Hi guys. I’ve used Audacity for quite a few projects now (brilliant software, keep up tthe hard work guys) but I’ve just only recently starting using it to record my drumming.

Long story short, there’s a really fast song that I can play just fine when not having the pressure of being recorded, but of course I miss a few beats when I hit that magic record button.

I came up with an idea: take the tempo down by 25% in audacity, then play the track through headphones whilst recording the drums directly to audacity. I then expected that I could simply add 25% tempo to the drum track and lay it over the original mp3. Makes sense right…?

My drums end up being slower than the original track, even though all I’ve done is take away 25% then readd it. Am I missing something here? Are the calculations different when converting back to ‘100%’?

You’re not the first to be confused by this, and I’m sure you won’t be the last

If you change the tempo by 25%, then the new tempo is 75% of the original tempo. That is, the new tempo is 75/100 times the original tempo, which is 3/4 of the original tempo.

To “revert” to the original tempo, you need to increase the speed by the “inverse” amount - that is, 100/75 or 4/3, which equals 1.33333333 times faster. So you need to increase the speed by +33.33%

Fortunately there is an easier way to do this.
Make a note of the length of the original track (in seconds) before you slow it down, then when you want to speed it up again, just enter the original length (in seconds) as the new “To” length (bottom right box in the Change Tempo effect).

Note that the Change Tempo effect does cause some damage to the sound.
The Change Speed effect causes far less “damage”, though of course it does change the pitch as well as the tempo - you may get away with that if you tune your drums a bit lower than normal.

You legend! That worked a treat, beat perfect again. Thanks matey. Maths…not my strongest subject in school, I figured I’d have a calculator when I got a job