In the upcoming Landscape showcase for 4.2 I set up adaptive music that fades between two tracks based on your location in the level, fading from an upbeat version of the music to a quiet, more atmospheric version. The two music tracks are in a sound cue, and their respective volume levels are faded in an out by a float parameter being set in the level Blueprint.
The sound cue for the music looks like this:
The continuous modulator nodes can change the volume and pitch of a sound based on a float parameter, so the top one is set up to fade the volume from 1 to 0 as the parameter increases, while the bottom one fades from 0 to 1. The mixer node just adds the two sounds together.
In the level Blueprint, the parameter is being set for the sound actor like this:
I left it out of the screenshot because it’s not strictly relevant, but the music fade value is being set according to the player pawn’s Z location normalized to a range (so you get a result going from 0 to 1). The fInterp node is used so that the float parameter updates smoothly instead of suddenly popping from one value to another, which would sound jarring.
This particular setup is for two versions of a music track that need to sync up precisely, but there are a few other ways you might manipulate music and other sounds with Blueprints too - it just depends on your needs.