Each of Traktor's virtual turntables has an icon in the upper-left corner that says "SYNC." Make sure that this button has been clicked on each turntable, The icon will be colored in yellow when this is done. This will enable Traktor's automatic sync capabilities.
Traktor automatically assigns a "beat grid" to each song in your music library. The beat grid allows Traktor to determine the tempo of each song and to play it back at the same speed as others. If you still have problems after enabling Auto Sync, check that the beat grid is accurate by viewing the end of the song in the audio window. If the grid does not line up with the beats, click "GRID" in the lower left corner and use the grid slider button to line it up.
Even with Auto Sync enabled and an accurate beat grid, some songs will not sync with each other because their tempos are too far apart. Traktor can slow down or speed up songs by an amount that is adjustable in the program preferences. Click "Preferences" and then "Transport." This will open the"Pitch Fader Range" menu, which you can adjust up to 100 percent. Doing this will allow for extreme tempo variations.