This is weird because I did not know how to ask this question. Let's say I want to remix a song. I have pre-record of the drums I want to use and I loop them... they are fixed of course of BPM (This is not a Midi track is a already wav file looped). And I also have the voice I want to remix with this drum.

The problem is that they are in a distinct "BPM" or speed so I would like them to match... how can be this done without say affecting say the pitch of the voice or the sound of the recorded drums?.

Basically want I want to do is something similar to what you use software like Traktor that you can loop a song and move the BPM to match the one in another deck.

I am using Reaper right now. It has the option of detecting/setting the BPM but of the overall song... not of a particular track.

  • what DAW are you using? some do this automatically. And you want to only change the BPM of the loop, not the whole track itself, right? That is how I'm understanding it from the way your questions is worded.
    – Travis Dtfsu Crum
    Sep 24, 2012 at 17:05

3 Answers 3


Reaper can set the tempo at any point during the song, or smoothly transition from one tempo to another over a fixed amount of time.

Use the Time Signature/Tempo Change option from the Insert menu, and to gradually move the tempo from the BPM of the section you mixed in from to the BPM of the section you will mix to, just use the Gradually transition tempo to next marker option.

  • But this will allow me to have a Tempo in one track "faster" than the other one? or this is project wide?
    – mfcabrera
    Mar 12, 2012 at 10:43
  • You can change the tempo in any track.
    – Rory Alsop
    Mar 12, 2012 at 10:54

You are talking about changing the tempo of a track. This can be done with many tools (probably all tools you would call a daw) including Reaper.

There are basically two approaches.

Compressing the wave. Imagine a given file of audio data is 44100 samples long and this took 1 second to play. If you kept all 44100 samples but changed timing so that that all played over a half a second, you would be compressing the wave. This approach will alter the pitch. Another way to think of it is turning up the speed of a turn table. Faster means higher pitch. Old jazzers and some guitar players would play a record at half speed in order to slow down fast passages and play along. This resulted in the same sound pitched almost an octave below the original. Fine to jam and practice with and at a reasonable pace for a student.

Interpolating a new wave. The idea here is to change the tempo without altering pitch. It is not immediately obvious how to do this computationally and involves some linear algebra. If your a programmer and are interested, I am reading a book by Craig Lindley that includes some easy computational algorithms in java that are open source and I could send to you.

Pragmatically, you should do this with Reaper or whatever other tool you are using. (Ableton, Audacity, etc.). They will almost certainly support method 2. But beware of the difference, and realize that you might be able to get away with altering the tempo of a drum track via method 1, as percussion is less prone to clash other parts of the mix because of some arbitrary shift in pitch. Imagine a vocal track on the other hand, whose harmonic relevance to the rest of the piece could be destroyed by a x.17% change in frequency.


There is a tool by propellerheads called recycle http://www.propellerheads.se/products/recycle/. It allows you to input audio and it detects transients and allows you split the file up into each drum hit or output to a file format called REX (which most modern daws accept). It is a very handy tool and will probably do you want. You can either drag each hit onto your track or you can drag the while rex file on and re-arrange until it fits your current tempo.

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