Music

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

It can be customised on the "Options" menu.

Music Track List (on Bandcamp)
Checkpoint 6, Checkpoint 7, Endless and Versus/Co-Op have some significant errors in the music.

Role in Gameplay
*Smash Hit's music is composed to be synchronized with the gameplay; for example, when Falling Glass Planks fall in Checkpoint 3 room 4 part 1 (second part is out of sync) you can hear a rumbling sound in the music.
 * When the tone changes to signal the beginning of stage 2 of Checkpoint 10, the speed increases by a large factor.
 * Checkpoint 10 stage 2 also shares a similar rhythm to Checkpoint 3 stage 4: overlap the CP3 stage 4 walkthrough with the CP10 stage 2 music, every time there is an abrupt change in tone, expect Falling Glass Planks to fall.

Unused Tracks
Note: Some of these are from old versions of Smash Hit and aren't present in the final game's files. These soundtracks can be found only in mods of version 0.8.0. However, not all soundtracks are found.

Other

 * The only time the music is used outside of any Mediocre game is a Roblox game known as Ultimate Marble Rider (this is because it contains Smash Hit music and that it mentions Douglas Holmquist (who is the music composer)

Early Music Sketch 1, 2, 3
Douglas Holmquist, the composer smash hit music, decided to make Early music sketch which was actually used in Custom hit for some weird reason, the first one actually resembles smash hit 0.1 which was the very first ever version of smash hit to ever exist, if they actually know what they're doing, these actually are a forgotten pack of music used in the first version of smash hit not to be confused with the first soft launch, this one explains the beauty of how it used to be.