It's in "The Big Book of SONAR Tips"
https://shop.cakewalk.com/1244/?scope=checkoutrc&id=j3dXaNuxgP
 
Chapter 12: Tempo and Pitch Shifting
Les Paul’s Double Speed Tape Trick
 
Also here.
http://www.soundonsound.c...hniques/vari-well-then
 
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Another method is what jimkleban described but even simpler, no need to use third party Kontakt.
1. Make temporary mix of your song to a new track: Tracks> Bounce to Tracks.
2. Insert DropZone synth.
3. Drag the temp mix clip into DZ sample window.
4. Insert C4 midi note into DZ midi track. The note has to be twice as long.
5. Freeze the synth.
 
Now you can record your part and then and do the same procedure with the recording, this time inserting C2 note.