Pioneer Dj DDJ-FLX10 4-Channel DJ Controller for rekordbox and Serato DJ Pro (Black) - Manual (Page 124)

Serato DJ Pro
124
En
Advanced use
Using 4 Beat Loop
While a track is playing, press the [4 BEAT/EXIT] button.
Loop playback starts with 4 beats from the point where you press the
button.
 Canceling loop playback
Press the [4 BEAT/EXIT] button.
When the loop out point is reached, the rest of the track continues to
play without returning to the loop in point.
Using Manual Loop
You can use Manual Loop to choose the section you want to loop in a
track.
1 During playback, press the [LOOP IN, 1/2X] button at the point you
want to start looping (the loop in point).
2 Press the [LOOP OUT, 2X] button at the point you want the loop to
end (the loop out point).
Loop playback starts.