How does one design sounds for an FPS? Anyone who’s seen those viral videos of someone accidentally pistol whipping themselves will tell you it’s a lot more complex than just pointing an iPhone at a glock to get a gun sounding like, well, a gun.

We spoke to Stephen Miller, Audio Director at Infinity Ward about all the intricacies of making a gun sound as it should, and the high cost of broken equipment that might come with such a dangerous endeavor.

The biggest takeaway is basically just how Infinity Ward have broken apart the physics of what a gun noise actually is, and just how much technology goes into the new Call of Duty to make blasting enemy combatants to bits sound authentic, rather than a single WAV file on-disc.

This console generation has a huge emphasis on 3D audio, especially with the PS5. When you were mixing the sounds for MW2, were you doing so with 3D Audio in mind?

Stephen: Well we’re still mixing, but yeah we do support 3D audio on the PlayStation as well as another version on consoles and Windows. When we’re mixing we have to make sure it sounds good on everything from Stereo TV speakers all the way up to full 7.14 surround. We do absolutely make sure that it sounds good on everything.

Considering Modern Warfare series is one of the more narrative driven Call of Duty series, what was it like having to choose between having something sound more cinematic vs having it work better for gameplay?

Stephen: We do try to make one game. MP, SP, Co-Op all have different sound to them, especially for anything that gives gameplay feedback. Footsteps, the guns anything that’s supposed to give you some kind of feedback that you need to pay attention to what’s going on. In campaign we’ll have a cinematic moment, and we’ll custom swap out sounds just for that.

It’s more for bigger scenes. Helicopters that fly in and shoot at something, or a big tank. More artillery than the small arms stuff. But we have had, where if we have a slow mo thing or any kind of special scene in campaign, we will do custom sounds for that as well.

Speaking of tanks, I was surprised to see you used real tanks for the effects.

Stephen: We’ve done quite a bit of recording for this project. 3 helicopters, various tanks, artillery, all the small arms, rocket launchers. You name it, we tried to record it.

So having done all this, walk us through what makes something sound like a tank then?

Stephen: When we record those things, we’re usually recording on a close-up and we’re recording on 50-60 different channels. Some of those are Stereo Microphones, some of those are mono. So you’re looking at somewhere between 30-40 microphones at varying distances. And then additional microphones at further distances to get that perspective as well.

Having a tank fire its main gun is not exactly inexpensive so we tried to optimize recording it as best we can.

When we break down a gun as a player, from that perspective: There’s a shot, there’s the mechanics of it- the metal clanking. There is the low frequency effect, the big bass-y rumble, and then we have the tail or the projectile, so you hear it going off into the distance.

And we break that all down into individual parts by using different types of mics and placements to get all those individual sounds so that when you pull the trigger and go bang, we get all 4 of those plus you’re getting our reflection system.

It’s raytraces that reach out into the world, it finds points to interact wiht from Geo on the side of a building or a mountain in the distance. It’ll play a reflection sound off those. Every time you pull the trigger of any gun, whether it be a tank or small arms, you’re getting 12 or 13 sounds that play at one time. All to kind of always be changing, all to always be making you feel like you’re in your environment so that it doesn’t feel repetitive. It feels natural.

So it uses the geometry to indicate what kind of sound it plays back?

Stephen: Yes. That way we acn also do different sets. So if you’re in an urban environment you get different types of reflections than if you’re in a big open desert.

Related to the raytracing you mentioned, does that use the same technology as graphical raytracing?

Stephen: It’s similar. All it means is that it has a source and it reaches out and draws a line mathematically until it hits a point or geo in the world. It is a less expensive version than a ray than what is used for the visual part. They trigger often. Every time you fire an automatic weapon, it fires a ray. It’s doing a trace.

 So past gen consoles would use this too?

Stephen: These traces are very inexpensive so we can do a lot of them.

So having all those microphones near weapons firing is a little bit like having a baby in front of an alligator. What was that like?

Stephen: I’m gonna quote you on that at some point [laughs]. Different Microphones have different SPL levels and have different uses. We have to be very careful and we have blown up microphones in some of our recording sessions. So basically you put something that’s a little too sensitive too close to something that’s high SPL and it blows up the diaphragm- it’s done.

Through the years and through a lot of experimentation and some failures, you’ll learn what can be where based on how loud something is. If we’re talking suppressed weapons, a lot of those things can get much closer because that’s not a lot of SPL.

The second the suppressor comes off, you back off a bit. As you get into larger caliber things you get further and further away. We’ve definitely had some failures.

When we’re field recording everything is inside what we refer to as the Zeppelin. Over the top of it is the fuzzy or the furry for wind. It really helps so if there’s any wind it doesn’t hit the diaphragm and cause that fluttering noise.

Is there anything sound-wise that you guys are especially proud of?

Stephen: There are definitely things that I gravitate towards. It could be an edited scene or an execution sound for multiplayer. Jake has been working on those and there are certain ones that are like “oh that is so incredibly satisfying”. I know when I go play I’ll want that operator with that assigned to it.

There are also certain weapons that I’m absolutely in love with not because they perform well necessarily, based on my playstyle. Simply because I like how it sounds and I wanna hear it over and over again.

We put a lot of love and attention and blood sweat and tears into the weapons from every stage from how they’re chosen, animated, recorded, how the sounds are made, how they’re mixed into the game. It’s really important to us.

 Is there anything you wanna say to the APAC fans?

Stephen: There are lots of exciting things to look forward to sound wise. We also have a lot of new technology that’s in MW2. We have an entirely new occlusion system. When geometry gets in the way, it occludes [the sounds]. We have a brand new convolution reverb system. That is particularly fun for us because it has you go to a location and it adds the right reverberance to it. You can record an impulse there. If we go find a particular warehouse and think it sounds cool with the reverb, we can go in and capture an impulse, and take a recording and it drops straight into the game and every sound gets processed into that reverb.

Rather than trying to do it synthetically with some kind of reverb, you get something that’s really natural.

With Call of Duty Modern Warfare II due out in October, there’s plenty to look forward to. With its focus on an immersive sound experience, it’s definitely something you’ll want to check out with headphones at least once.

Our thanks to Stephen for sitting down and talking shop with us, and don’t forget to check out our other Call of Duty Modern Warfare II interview as well.