What may be Halo's biggest audio innovation is O'Donnell himself, or rather the position of audio director. He's not the guy who wrote the music and handed it off to the executive producer. O'Donnell spends months in the stripey room, checking and tweaking the mix of score and effects, listening to the rattle of fragmentation grenades against the band that represents wood, then the one that's rubber, and making sure the muffled thump of an underwater explosion isn't lost in one of the countless overlapping layers of music. It's a role that doesn't even exist in the film world, where the final audio mix usually falls to the director and editor. From what I heard in O'Donnell's office, Reach's audio is just as painstakingly curated as the rest of the series. The adaptive scoring is more sophisticated, there are more layers to trigger and the variety of sound effects is industry-leading. That's the easy part. What's harder to understand is why Halo's music, the soundtrack of a sci-fi war, is so consistently refined, particularly when compared to other games.