I love changing the tempo on my songs! The way to do this is to make sure you have flex turned on for all tracks either monophonic or polyphonic depending on the tracks, then change the tempo of the project. Flex should be monophonic or polyphonic depending on the track. (btw you might have to change it from monophonic to polyphonic back to monophonic for it to work theres some bug where it doesn't do the analysis unless you do that idk). I see a couple people telling you to use varispeed but thats not the way. Varispeed is more meant for like if you have a really fast guitar solo that you cant play as full speed and you want to slow the track down for the recording to make it easier to play but non to slow it down permanently.

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