A couple years ago, Jon Burton, founder of Traveller's Tales, shared pictures of a cassette tape made during the development of Sonic 3D Blast. This tape contained demos of the game's soundtrack, composed by Jun Senoue. These demos were created with keyboards and submitted for approval before being programmed into the game using the Genesis' sound chips.
Today, those tracks were finally released! ...Partially. The video above plays the first three songs on the tape: two variations of the opening and the "Powerup" theme. Presumably, more will be uploaded in the following days. Keep an eye on the GameHut YouTube channel for further uploads, and check out tons of behind-the-scenes content regarding classic Traveller's Tales games, including Sonic 3D Blast and Sonic R!