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"The Use and Effectiveness of Audio in Halo: Game Music Evolved" by Aaron Marks and Martin O'Donnell
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Aaron Marks: I bought my Xbox because of the game HALO. I was looking for a great game and this had its share of recognition, which I really couldn't ignore. I'd seen several demonstrations of the game over a couple of years but the one that really stuck in my mind was the Xbox demo Bill Gates gave at GDC 2001. My jaw scraped the floor ogling the graphics and realizing what this platform held for the future of game audio - I had to have this game!

Because I'm a late bloomer, I seldom get any new product the minute it is released, instead I wait until the bugs are worked out and the cream floats to the top. The one game that kept floating to the proverbial top was HALO, and I kept hearing great things about the audio! I picked up the soundtrack well ahead of getting the game and became quite familiar with it. But, instead of cheaply satisfying my listening urges, it primed the pump for the gaming-playing deluge to come.

Being a game composer and sound designer (and occasional writer) I am always championing for the effective use of audio to totally immerse the player into the game world. The music sounds great on the soundtrack alone, but hearing it as intended in the game is entirely another experience altogether - it's purely cinematic! In fact, the rest of the audio hits the mark with equal accuracy. The sound effects are dead on.

The narratives and dialog were true and professionally acted. The implementation is impeccable. And experiencing all of this audio glory in full Dolby Digital surround on a wide screen home theater system is the pinnacle of gaming heaven. Finally, someone got it right! Man, I wish I could have done this game!

Martin O'Donnell: I feel really good about the final outcome. It's funny but towards the end of the crunch time, I was pulling my hair out trying to get more mixing time. So much of the audio was implemented in the final weeks before we went gold and had never really been tested to my satisfaction. I was worried that the audio in the game hadn't been balanced enough and would not have the final polish that I expect from a finished product. Somehow, by the time the game shipped, the polish was mostly there, polishing fairies perhaps. I would say that I got about 90% of what I wanted - I'd still love to tweak that last 10%.

A couple things worked better than I expected. When I finally got a chance to play through the game in the comfort of my own home, there was a point when I commandeered a Banshee, flew up into the cold, snowy night sky and a piece of music started playing that actually gave me a little spine tingle, and I knew it was coming! The other thing that was quite satisfying was hearing the Marines around me in combat, sounding as though they were real soldiers saying real stuff. I remember being in a battle beneath a Covenant ship that lasted at least 15 minutes and not hearing any of the Marines repeat a single line. The system for the AI dialog was one of the last things we implemented and it was great to hear it working so well.

Aaron Marks: I know what you mean about 'spine tingling'. There is just something about how a well thought out soundscape can totally absorb a player and create that emotional link. I remember fighting a vicious battle against an onslaught of Covenant, wiping my brow and hoping for a little break before the next engagement. I turn a corner and there's that music starting uh, oh this doesn't look good for our hero.

I'm always big on the overall 'soundscape', especially in expansive games like this. My impression of Halo, there is a nice layering of music, sound effects and dialog, all of which can be heard and understood out of the box without any manipulation of menu controls. The sounds which fade out when another of higher precedence plays is seamless. It's like a well planned project where audio was given top priority. It also says much for your talents, managing a project of this scope and getting it right. This game will be an example of how to do game audio right, from the score, to the sound effects to dialog, all extremely effective.

Martin O'Donnell: We had a pretty extensive plan before we even started producing content. Although towards the end it seemed like I was running around keeping a bunch of plates spinning and basically just trying to watch which plate was about to fall, the initial plan was still important. Part of my ability to manage the whole thing came because I had no other project to work on. Until Halo, I had been running my own business and had other clients and projects. With Halo, I thought of nothing else, probably almost to the point of obsession (I'm getting help, don't worry). But this enabled me to pay attention to every detail of implementing audio. Jay Weinland, my right hand man here at Bungie, and I shared the same vision for Halo's audio and it was a relief to know that someone else was being as compulsive as me.

I put some pressure on myself by making an issue of having no audio menu controls. My point was that our hardware target was one platform, the Xbox, and everyone would hear the mix I intended. If they didn't like it, they could blame me, but I didn't want people messing with the global mix of the game before they even got past the tutorial. Interactivity can mean a lot of different things, but giving people the option to re-mix the audio isn't one of them, at least for me.

Aaron Marks: I like it! A developer who's not afraid to stand up and take responsibility for the audio mix. I hope we'll see more of this trend in the future.

The musical score is especially important in this game. It seems that one of the general misconceptions in the industry is that the music has to play full blast ALL the time. The music dynamics here are perfectly implemented. It doesn't play constantly and I find that the silence really gives the music more impact. There is no sense of the introduction of the music being rushed, it can start out with a simple held note, like high strings subtly adding appropriate tension. As the mission or situation becomes more intense, the music will morph into a more dramatic soundtrack or step down proportionate to the number of bad guys left.

Martin O'Donnell: Well, what you're describing is the approach that film composers take when scoring movies. Of course making this happen during an interactive section of the game rather than just during the cut scenes does take some extra thought and work. I sat with the level designers and "spotted" the level as though it was a movie, with the knowledge that the music would have to be malleable rather than static. I had a system that would allow the game to trigger the start, the stop and a transition within each piece of music. I tend to write and produce linear music, pieces that have a beginning, middle and end. Sort of like almost all other music ever written perhaps? All I needed was a way to extend, contract or vary the middle section in real time.

Most pieces could be dissembled and remixed in such a way that would give me multiple, interchangeable loops that could be randomly recombined in order to keep the piece interesting as well as a variable length. I also would make alternative middle sections that could be transitioned to if the game called for such a change (i.e. less or more intense). If I needed a bigger contrast I could always start a new piece and have it either interrupt or cross fade with the piece already playing. Since I could have more than one piece playing at a time, I also made "stingers" that could just be laid over the top of another piece. It was important to experiment with all the possible combinations that the game might come up with to ensure no horrible, unintended clashes. Most of the time it worked pretty well.

Aaron Marks: It's certainly seamless to the player and at the same time allows for variation during repeat plays - a great way to keep the player coming back for more. Technically, the music implementation and mixing of these various pieces I'm sure was almost as difficult as composing an appropriate score.

Martin O'Donnell: Well I believe that there are three equally important stages for game audio: producing content, implementing content and mixing content.

Aaron Marks: By the way, did you or the development team use sound tags, scripting or make use of something like DirectMusic Producer?

Martin O'Donnell: DirectMusic Producer is a bit more MIDI based than I was comfortable working with. Our tag system lets me record high fidelity music and audio, using live musicians or MIDI instruments and then cut up the files into usable chunks. The basic sounds are put into sound tags that are then available for even more complex sound tags. This basic building block is a tag that consists of randomly weighted, audio files that can also have ranges of amplitude and pitch. If it's a dialog tag, it can then be put into the "Uber" dialog sound tag and used for combat dialog for example. Music and ambient sound tags are put into complex looping sound tags. It gets even more complicated and my head hurts just thinking about it. However, it's worth the effort and it's great having programmers who dedicate a bunch of their time making a sound engine work so well.

Aaron Marks: A neat example of how that dedication paid off in the presentation of the music was its use in musical foreboding. When you are in exploration phases of the game, not quite sure of what you are looking for or where you are going, the music definitely lets you know when you may be close to something of importance. The same of when you are done in a certain area, the music slows or stops all together. I assume you had a bit of a role in that idea.

Martin O'Donnell: Yep, that's pretty much the subject of conversation while sitting with the level designer and "spotting" the level. Instead of a director telling me where to bring music in and out, the level designer would tell me what he hoped a player would feel at certain points or after accomplishing certain tasks. I would go back and develop appropriate music cues, then have the designer script the cues into the level, and then we'd play through it to see if it worked as desired. One of the things we would also script is a "bored now" switch that would fade the music to zero if it's gone on too long and the player hasn't made the progress we expected.

Aaron Marks: Now, what about your mindset behind creating the music? When composing a game like this, I'd consider making the overall mood a little dark and uneasy, like anyone would feel in a strange world with aliens running amok. At the same time, the mood would have to be somewhat heroic, making the player feel like they are accomplishing something important. I can certainly feel this in Halo, always feeling a little uncomfortable but running around with my chest puffed out ready to take on the challenge.

Martin O'Donnell: The first words that were used to describe Halo to me were "ancient", "alien" and "epic". The first piece I wrote basically turned out dark but heroic, which is another way to describe the feelings evoked by those words I suppose. After composing the theme, all the other pieces were based on that same emotional premise, although there are some individual compositions that stray a bit. The first public venue for Halo was during Steve Job's keynote address to MacWorld 1999. We had the ability to show the great graphics engine but had absolutely no sound engine. That was my chance to compose and produce a piece that would grab people and tell a big epic story. I figured plainsong chant for the "ancient", Qwalli chant for the "alien" and orchestral strings and percussion for the "epic". It was a great way to introduce a game score to the public; I was quite fortunate.

Aaron Marks: The sound effects are also an important part of the soundscape. In this case we have a mixture of human and alien weapons and machines which, even though completely made up, have to sound believable in order to keep the player 'in' the game. Overall, my take on the game is there is a good choice of convincing sound effects. The Marine weapons all sound familiar and give the player that sense of believability, hearing standard gunshots and bullet hits like we've grown used to. The alien weapons all sound 'foreign' and definitely from another world.

Martin O'Donnell: For sound effects to be believable they first and foremost have to be in perfect sync. The best sound effects in the world are useless as soon as they fall out of sync with the action on the screen. Even effects made by simple mouth noises will work surprisingly well as long as they're in sync. This is a lesson learned in linear mediums that the interactive medium is still learning. In Halo, the human weapons, vehicles, explosions, and such, are all based on recordings of real stuff from our world. They've been sweetened and enhanced in ways that might make them more "meaty" but for the most part they should be recognizable even separate from the visuals. Being in sync with things like metal scraping against rock walls, or tires skidding on sand, or shell casings bouncing on every kind of surface, has more to do with the implementation of sound playback than simply creating a convincing sound. For example, the game keeps track of every shell casing and its impact velocity as well as the surface that it's impacting. We create a sound for the casing bounce, sweeten it with the sound of the impacted surface, and change its amplitude with the velocity. That really helps to bring a level of reality to every physical thing that happens in Halo. As far as stuff that needs to sound "alien", we end up relying a bit more on more synthesized sounds and also actual mouth noises (for the "Flood").

Aaron Marks: You make a great point here, Marty, something developers and sound designers don't often think about. We often get so tied up in creating great 'sounding' effects that we don't pay the needed attention to making sure they mesh with the action. This is definitely the game to make a good argument with.

Martin O'Donnell: The other important factor for sound effects is balancing the volume realistically. Soft sounds should really be soft, in order for loud sounds to seem loud. This might seem obvious, but I've heard plenty of games, that normalize every single sound effect to the maximum volume and it ruins the believability of the sounds themselves.

Aaron Marks: You bet! Hearing footsteps at full volume takes away the impact of those more satisfying sounds like gunshots and explosions. Implementing sound effects is an exercise in subtly for sure. Imagine a music mix where all of the instruments were turned up full blast. It would be deafening, not to mention completely chaotic. Herein lies the true secret.

Since we are on the subject of subtly, lets talk about how you got those wonderful background ambience sounds to add to the experience and not become just another layer of noise. Even with all of the music, sound effects and narratives going on, the ambience really makes the entire world believable.

Martin O'Donnell: We used the same tools and tag system that we used with the music. I always felt as though basic ambient sound could be done better even in films. We made stereo loops of varying lengths that can play back in randomly weighted order. We have multiple detail sounds that play at random intervals, random volume ranges, random pitch ranges and random 3D positioning. In addition we can attach the same system to objects or devices that exist in the environments. So, for example, if you stand on Halo you will hear a basic outdoor stereo sound that surrounds you (full volume on the front speakers and half volume on the rears) plus random wind gusts, birds and animal sounds that are randomly heard in various locations around you, and the waterfall crashing on the rocks to your left. This all turns with you as you turn, except for the basic stereo ambient bed which will keep its pre-rendered positioning. It felt better to me to have at least one basic element that wouldn't go swirling around your head every time you looked around. We can also have multiple tracks of stereo ambience playing simultaneously, which means that even in the basic stereo bed, there is almost no chance of hearing something exactly repeated the same way twice.

Aaron Marks: Those techniques sound very similar to the use and positioning of the alien and human vocalizations as well. Nothing like hearing a little alien voice saying "More here!" in the front left speaker to alert the player. I especially thought it was very effective when I happened to be turned another way and heard it behind me. It really gets your attention.

Martin O'Donnell: Those voices are technically identical to the sound tags that are attached to weapons or vehicles for example. However, the "Uber" dialog tag controls them. This tag tells the AI (like the grunt) what sort of thing to say based on several factors such as spotting an enemy, seeing a dead comrade, feeling intense pain and the like. When you hear the grunt say, "More here!", it's because he spotted you, knows you're an enemy and is aware that his buddies are near enough to hear him and help him. In that case he could have said several different lines that would have communicated the same thought like, "I see one", or "Yikes!". The number of dialog lines we recorded and edited for those types of dynamic situations number over six thousand.

Aaron Marks: Overall, I thought you guys did a great job with the different voices and actors. You get the sense that there is a whole unit of Marines with you during those intense search and destroy missions. The aliens are very well done. Since making these alien creators sound believable is a very tough job, I can appreciate the efforts involved, script writing, auditions, the recording sessions and editing - quite a job. I love those little grunts, their voices and their humorous lines, it gives the impression they are rather harmless while adding some fun to an otherwise 'serious' game. Whenever you hear the chilling, monstrous scream, you know a more potent bad guy is too close for comfort and you'd better do something quick. The AI voice (Cortana) is a nice addition too, giving clues and helping the story along. Obviously there was some serious thought and planning to get the dialog just right.

Martin O'Donnell: We started working on the various scripts for Halo quite a while ago. We had produced several "movies" using captured in-engine footage and post-produced the music and sound design. For the 10 minute long E3 2000 trailer, we had gotten to the point of working from a script with character descriptions and a storyboard. I've always believed in casting professional voice talent, in particular actors who are used to being in recording studios and working with a microphone rather than on a stage or in front of a camera. Many times the best voice actor is not necessarily the best actor on stage or screen and vice versa. We've struggled a bit with the whole "celebrity" idea as far as voice talent in our games. However, there's no doubt that although we probably won't sell more titles because of a "name" voice actor, we absolutely want to get the best person for each role. We knew the characters we were looking for and what sort of voice we wanted, we held casting sessions up here in Seattle and also used several voices from Chicago, people we had worked with on past projects. It's always great to find actors who are able to add something to the script. I enjoy getting several good reads of the scripted lines and then asking the actor to improvise a little based on their understanding of the scene or situation. For the Marine dialog, the improv stuff was invaluable. Cortana was a difficult character to cast. She needed to be an all-knowing AI, with an attitude, but still be likable since she would be inside your head for most of the game. In the end all the voices were hired from outside of Bungie except for the Grunt (our cinematics director Joseph Staten) and the Hunters, Jackals, and Flood (which were all me). Of course there were other cameo appearances by other Bungie developers, mostly one liners delivered by crewman just prior to some horrible death.

Aaron Marks: I definitely agree that seasoned voice talent is the way to go for a project with this much dialog, you really can't beat it. Unfortunately I've heard some pretty bad acting on otherwise great games and it really brings down the quality of the production. That's something to be mindful of when casting ourselves or our colleagues. While it can be convenient, and even a great moral booster in the company to say "I'm the death sound!", it has to sound right for the character and the game. You guys nailed it!

So, let's see we've talked about the soundscape, music, sound effects, ambience and dialog for Halo. I think we've probably learned a few lessons along the way, and since this game was so well done, I think it was a great example of how to do it right. Halo 2 is just around the corner and the same sound team is back for the second round.

Martin O'Donnell: We'll be pushing the boundaries of each area even further in Halo 2. The AI conversation system will be many layers deeper and more complex. The dynamic music system will have more tracks, markers, and triggers to enable even more interactivity, without turning it into a music game, of course. The physics engine will work more closely with the sound engine to enable even more responsive sound effects. There will be real time control over DSP effects other than just reverb that should help to make the environments even more realistic.

I want to make sure that we have the time to do more Foley work from the ground up. I want to make sure that we have the time to have real musicians performing on any piece that needs it. I love the sound of real strings but sometimes, for example, I like to use a Mellotron sound because it's creepier. I want to be able to make that choice rather than have the schedule make it for me. We will still use some ADPCM compression, however all our sounds will be at 16 bit, 44.1 KHz. No more 22k sounds. Also, our voice talent pool will have no constraints. We won't be hiring celebrities based on their marquee status, but their talent. Who knows who might show up?

Aaron Marks: Is it all new music and sound effects or will some of the familiar elements be back?

Martin O'Donnell: The plan is for everything to be new. However, that doesn't preclude reusing something that just works great or has sentimental value. Also, certain Halo musical themes will probably get a bit of the old variation treatment. On the graphics side of things, familiar objects will look similar but way better, the same will apply to the audio side.

The audio in Halo received some pretty major accolades from some places as diverse as Game Developers Conference and Rolling Stone Magazine. I'm probably most satisfied with the fact that the audio in Halo has seemed to help raise the interest in game audio by game developers and publishers. The public is ahead of the curve in this regard. Now, more than ever people who make games seem to understand how important it is to pay attention to producing and implementing audio at a higher level of quality and technical skill. The public is listening to games on the same platform and same home theater that they listen to movies, music and television. We have to be able to meet or exceed their expectations.

Aaron Marks: Indeed we do.

Aaron Marks, when not discussing great game audio with other composers and sound designers is actually one himself as the proprietor of On Your Mark Music Productions. He is currently hard at work on projects for 1Up Studios, Beyer Productions and Enemy Technology. Aaron is also the author of "The Complete Guide to Game Audio", published by CMP Books.

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