This is probably the first time most of us have heard these tracks as they were intended.
For the first time in digital quality, you can hear Marathon's music as it first shipped in 1994.
The default M1A1 tracks use QuickTime 2.5, released in 1996, which changed some of the instruments. These files were recorded with QuickTime 2.0, which shipped with Marathon, to capture what it sounded like when Bungie first released the game.