Two generated loops at different tempos are loaded, or load your own tracks: the tempo and first beat are detected from the audio. Play both, match them with the pitch fader or sync, swap the bass with the EQ, and record the mix.
Speeding a record up also raises its key, like a voice on fast-forward. A few percent goes unnoticed; past about 6% vocals start to sound wrong. Key lock (time-stretching) keeps the key fixed while the tempo changes, at a small cost in sound quality.
pitch % = (target ÷ original − 1) × 100
semitones = 12 × log2(target ÷ original)
Two kick drums and two basslines together sound muddy and push the mix into distortion. The fix is the move most club transitions are built on: bring the new track in with its lows cut, then swap bass on a downbeat.
Dance music is built in blocks of 8, 16 and 32 bars: something changes at the start of each: a drop, a new melody, drums returning. Start deck B on the first beat of a phrase in deck A and both tracks change together, so the mix sounds planned rather than lucky. Sync in the decks above lines up the phrase as well as the beat.
Trim long intros, bring files into one format, or pull audio from a video before loading it onto a deck.