BPM, key and phrasing: the basics of mixing two tracks
Three ideas separate a transition nobody notices from one that empties the dance floor.
Mixing is making two songs talk to each other for a few seconds. For that, they need to match in speed, in structure and, ideally, in harmony.
Match the BPM
Beats per minute set the speed. Adjust the pitch of the new track until it runs along with the one playing, by ear or with your equipment's sync.
Align the beat
At the same speed, make the first beat of both land together. A kick slightly out of place sounds like galloping.
Respect the phrase
Electronic music is organized in blocks of 8, 16 and 32 beats. Start the new track at the beginning of a block, so the changes in both happen together.
Match the key
Tracks in compatible keys blend without clashing. Many programs show the key on the Camelot wheel: neighboring numbers match.
The EQ does the rest
Two bass lines at once muddy the sound. During the transition, cut the low end of one track and bring it back when the other leaves. That swap is the basis of almost every clean mix.
