From Halopedia, the Halo wiki
The Audio Testing Environment, known to Bungie employees as "the stripey room", is a development tool used by the Bungie audio team to test audio effects in a Halo game. The room, a playable space, was first introduced in an interview with the Halo: Reach audio team, where it was described by Martin O'Donnell as a "big test audio environment".
The "stripey room", in its current incarnation, is a long corridor set in the game environment with color-coded stripes of every texture and material type used in the game. The audio developers can then use this space to test various audio effects implemented into the game, as well as see how a piece of music feels in a certain environment. It also appears that any vehicle or character can be loaded into the game.