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I have a track recorded in reaper which I want to variably speed up and slow down as an effect behind my other tracks. Is this an option? Do I need a plugin?

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Just to be sure - is this an audio track or MIDI? By variable speed changes - do you mean you need gradual playrate transitions or just multiple steps? Is this for performing and you need live operation (and some handy way to control this) or precision is more important (final recording/bouncing)? –  Karol Piczak Jun 24 '13 at 14:37
    
Like a sin wave, so it speeds up and then slows down before returning to normal, so the duration over the course of the wave isn't changed. –  Matthew James Davis Jun 24 '13 at 17:30
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2 Answers

Your best bet with achieving this effect solely with Reaper is to use multiple (background) projects.

Move the audio track to a separate tab. Make sure that you have following options ticked:

  • Run background projects
  • Play stopped background projects with active project
  • Synchronize play start times w/ play background projects*

Then in the new (background) project you can apply playrate automation. First make sure that master track can be seen (View > Master Track). From available envelopes select Playrate and draw the automation values. Something like this:

Reaper playrate automation

You may probably want to select "Preserve pitch in audio items when changing master playrate" by right clicking on the Vari-Speed knob so that you don't get the chipmunk effect.

Manipulating MIDI tracks would be easier, as tempo changes should do the job, though you may still need to resort to background projects.

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Why did you italicize Reaper? Is there another DAW that can achieve this more effectively or more easily? –  Matthew James Davis Jun 24 '13 at 20:09
    
Okay, then I'll try this approach instead. Thanks! –  Matthew James Davis Jun 24 '13 at 20:11
    
Not sure. If you need live performance capabilities, then probably DJ software like Traktor or Serato would allow hassle-free beat matching. –  Karol Piczak Jun 24 '13 at 20:21
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I'm not really familiar with Reaper, but just tried it out with a short clip and it seems to work. This is not a real automatic way, and if you need to do this often this might not be suitable. Instructions are for the Mac, but PC function naming should be similar.

  1. Go to the place where you want to start the tempo change (place the playhead there).
  2. Click Insert -> Time Signature/Tempo Change Marker
  3. Keep values as they are, place a checkmark next to Gradually transition tempo to next marker and click OK.
  4. Go to the place of maximum speed, repeat step 2.
  5. Change BPM to a desired value and place a checkmark next to Gradually transition tempo to next marker. Hit OK.
  6. Repeat step 4-5 on the place of minimum speed. You can do this at multiple points on your track, depending on your speed-up/slow-down needs.

You could try using the Time Signature/Tempo Change Marker found in the Insert menu

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Solid, will try it when I get home. –  Matthew James Davis Jun 24 '13 at 19:23
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This will only work on a project (song) level though, so all tracks will be affected. –  Karol Piczak Jun 24 '13 at 19:28
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And I forgot to mention - this would apply to MIDI tracks. Gradual tempo changes won't work for prerecorded audio content. –  Karol Piczak Jun 24 '13 at 19:35
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