FAQ: What is “1-beat cross-fade”? What is “smart cross-fade”?

A cross-fade between two tracks consists in fading out the first track (its volume goes to zero) while the other track is being faded in (its volume starts from zero).

Ask the DJ's 1-beat cross-fade consists in having the last beat of one track coincide with the first beat of the other, and cross-fading between tracks during that beat.

Ask the DJ's smart cross-fade consists in gradually shifting the tempo during the cross-fade, so all beats of one track match beats of the other track.

See also: Transitions