Music

In Smash Hit, the music refers to sound that is seperate from the in-game effects, such as balls being thrown, glass breaking, metal falling, buttons being pressed, etc.

It can be customised on the "Options" menu.

Bandcamp (made by Douglas Holmquist)
Checkpoint 6, Endless and Versus/Co-Op have some errors in the music.

Role in Gameplay
Smash Hit's music is composted to be synchronized with the gameplay; for example, when a Falling Glass Plank falls in Checkpoint 3 Room 4 part 1 (second part is out of sync) you can hear a rumbling sound in the music.