There are no rules … for starters 🙂
Having said that, it really depends on where you are going with your mix. Obviously if you are building up to a higher bpm climax you don’t want to go back. If you plan on hanging around the same bpm mark for a while and your next track is slower again (like another 123) then you could lower the playing track to 124 and bring the other one up to 124 too. And obviously if the next track is faster still, say 127 you want to bring that back to 125 for the mix since the playing track is already up. That’s what I do, but I know DJ’s that only go up, never down, so they would just raise the playing track even further to 127 and keep the new track at it’s original speed.
Again, not set in stone and everyone has his/her own way of doing things.
Greetinx.
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