Swapping basslines cuts the low end on the outgoing track to make room for the incoming bass

Bassline swapping is a core DJ EQ technique: as a new track mixes in, the DJ cuts as much low end as possible on the outgoing track (deck A) while leaving the incoming track’s bass (deck B) intact. This prevents the two basslines from competing in the critical low-frequency range, where masking and phase issues are most severe. Because bass takes up so much of a track’s overall energy, often very little adjustment of deck B’s mid and high range is needed to keep the mixed output’s levels acceptable. This technique is foundational for DJs mixing dance music where basslines define the groove.

Examples

In a DnB mix: deck A (playing) has its bass cut, deck B (incoming) is brought up. Crowd hears the new track’s bassline immediately. After a few bars, deck B takes full control and deck A is faded out.

Assessment

Walk through the steps of a bassline swap in a two-track DJ mix. Why is it mainly the low frequencies that need managing, and why is little mid/high adjustment usually required?