How Guerrilla Games created Horizon Zero Dawn’s remarkable 3D audio and sound

Earlier this year, we travelled to the Guerrilla studio in Amsterdam to talk to the audio team about the importance of sound in Horizon Zero Dawn and the ways in which the game makes use of the Platinum Wireless headset’s 3D Audio technology. The resulting video, which you can watch below, provides a brief but tantalising glimpse into the world of audio creation:

It became obvious that there was much more to cover regarding the audio in Horizon Zero Dawn, so we reached out to three members of the audio team – Audio Lead Bastian Seelbach, Sound Designer Pinar Temiz and Senior Sound Designer and Music Supervisor Lucas van Tol – to gain further insight into the team’s creation process, the challenges they faced and the creative decisions they made.

Defining an Audio Style – Bastian Seelbach, Audio Lead

When did Guerrilla’s audio team become involved with Horizon Zero Dawn?
Bastian: The audio team got involved in the early days of the project planning phase, helping to find a audio style that fit the initial vision for Horizon Zero Dawn.

During those days, a lot of the game was still in its conceptual stage. Research for Horizon Zero Dawn took a long time, as it was entirely different genre of game; this made it necessary for us to leave our comfort zone and approach a lot of things quite differently.

How did this approach differ from previous projects?
Bastian: The difference wasn’t just in terms of defining the audio style, which was unique and fresh, but also in terms of tackling the huge technical challenges ahead. A lot of our previous approaches to audio wouldn’t work anymore.

From a technical perspective, it was the sheer scale of the game that forced us to approach the sound design and most of the related audio systems very differently. While Guerrilla had a lot of experience with more linear first-person shooters, the world of Horizon Zero Dawn was entirely open. That made it necessary to find a systemic approach for a lot of things that had been hand-crafted up until that point.

To that end, Principle Sound Designer Anton Woldhek worked closely with Principal Tech Programmer Andreas Varga to hammer out the tools and systems we would need to ship a game like Horizon Zero Dawn. And, in the meantime, we started making decisions on what would become the audio style outlines for the game.

Can you give an example of systems you required?
Bastian: Some of the systems we required helped us place large parts of the content automatically, using a game data driven spawn logic. Other systems, like the ones we used for reverb and occlusion, helped ensure that our sounds felt natural within their position in the world.

How did you go about the immense task of defining Horizon Zero Dawn’s audio style?
Bastian: Horizon Zero Dawn is a huge game. It has a lot of different environments, cultures, wildlife and machines, as well as a fantastic story that ties the world together. The world offers a lot of contrast; while mankind lives in pre-industrial tribes, highly advanced machines roam the world.

Our approach to defining the audio style of Horizon Zero Dawn was to not nail everything down in one ‘audio bible’ from the get-go, but rather to follow an organic process of incremental decisions. You could call it an evolutionary process.

In fact, the entire studio was working that way for a while, as the world of Horizon was defined early on but the exact genre, its features and storyline crystallized over time. So the audio team had to make decisions based on the decisions that were made for the entire game.

How would you describe Horizon Zero Dawn’s audio style?
Bastian: If I were asked to come up with a name for Horizons Zero Dawn’s audio style, I’d probably suggest Na-Fi (Natural-Fiction). Whatever sounds were required had to be believable within the world first and foremost, and we are talking about a realistic, beautiful world. So the sounds we created had to be grounded and a part of their surroundings.

Creating the Machine Sounds – Pinar Temiz, Sound Designer

When did you start working on the sounds for the machines?
Pinar: Most of the core design and implementation decisions for the machines were made early on in the project. Of course, the machines changed and evolved as the project went on, but the core idea of giving them an animalistic and a high tech quality was born early on. Another constant was that the machines were going to be quite varied in terms of size, behavior and look and feel. We knew it was a wide spectrum.

How did you plan to implement such a large number of machine sounds?
Pinar: A large portion of the implementation methods we used were informed by our experiences working on the automata for Killzone Shadow Fall. The scope was vastly different, of course; the challenge wasn’t just striking a balance between ‘machine’ and ‘animal’, but also doing this for numerous machines in an open world, where they might appear in any number of configurations.

On top of that, we had to make sure that each machine type remained recognisable, yet coherent as a whole, while offering readable cues for gameplay-critical moments. And on top of that, we had to ensure that everything could be scaled, iterated, optimised and mixed.

That sounds like a tough act to balance.
Pinar: Oh yes! Another question on our minds from the get-go was how to tie Sound Design to AI, Animation and VFX, and yet remain independent enough to make creative choices that were not inherent in the machines’ original design documents – thus remaining purely in the audio domain, without needing to be addressed by those other disciplines. Luckily, our tools allowed for designers and coders to work quite independently, which meant one could implement almost any idea and see the results in-game without having to wait or tax on other’s time.

So how did you determine the right balance for each machine?
Pinar: In terms of content, it was a new challenge with each robot. Blending a lot of different sources was obviously a method we used a lot. You’ll find electronic sounds, real-life animal sounds and various kinds of material, from synthetic to organic – all edited and processed until we achieved enough variations and a tone that fit the machine. Our sources changed a lot based on the size of the machine, its function in the world of Horizon Zero Dawn, and its animation. The latter offered a lot of character cues for us to latch onto.

Can you give an example of these character cues?
Pinar: A classic example for us is the Shell-Walker, which came together relatively fast in terms of its sound design. Anthropomorphising the machines helps with drama, because the moment we first looked at it, we thought “He looks like a cute grumpy crab-guy!”

When you look at him you get the sense that he works all the time, mumbling to himself as he goes, obsessed with his little container box. Maybe he has a few colleagues that he hangs out with, but that’s about it – he’s constantly annoyed with something and has no life outside of work. These notions didn’t come from a document, they arose in our minds as we imagined how he might sound while he worked. And so the vocalizations were imagined and designed as close to that ‘feeling’ as possible, using both animal sounds and electronic elements.

Another example is the Watcher, which has its own character: more playful, curious yet dangerous in its own way. We always thought of it as a crazy Chihuahua. One moment it’s all cute and curious, the next it’s ready to bite your hand off.

Did you approach the ancient machines differently from the new ones?
Pinar: Certainly. For example, movement sound tended to be unified along machine factions. There are essentially two core factions: the new Gaia-designed machines, all futuristic, high-tech, efficient and clean. Then there’s the ancient machines, left over from the war, built using technology that is closer to what we see as cutting edge today.

Sonic differentiation between the two was based on the materials, especially the lack of vocalisations and the amount of metal and mechanical elements we chose to use. We also added elements to their movement sounds that stand out just enough for players to be able to recognise the type of the machine. This wasn’t just limited to subtle cues indicating their weight and size, but also encompassed details such as whether they carried liquids, like the Bellowbacks, and whether they had weapon systems with elemental effects.

The new machines are made out of exotic, futuristic alloys – how did you find a sound for those?
Pinar: Personally, I used very few metal sounds for the design of regular machine movements. It’s kind of a self-imposed limitation, due to the funny fact that I can’t listen to metal impacts or scratches for too long. Doing so causes very physical and uncomfortable effects for me: it makes me taste metal and feel textures in my mouth. I’m not sure if this quirk aligns with some sort of sound-touch/taste synesthetic experience, but it definitely makes it hard for me to work on metal sounds for long.

Luckily, I had an in-universe excuse: the machines are made of high-tech alloys that differ quite a bit from the metals we know today. I still recorded a lot of metal impacts and scratches, but I tried to avoid them where possible. Creatively speaking it made for an interesting challenge, communicating high-tech metal substances without using too much real metal.

Environment, Movements and More – Lucas van Tol, Senior Sound Designer and Music Supervisor

What were your first steps when you started working on environment audio?
Lucas: When we moved over to the Horizon Zero Dawn project, there was a lot of information available on paper, but not a lot that you could see and walk through in-game. This was the perfect phase to do some really in-depth research into things like wildlife. Wildlife was never something we had to particularly worry about in the Killzone games, but we knew we wanted this game to be full of life.

For weeks and weeks I scavenged every resource I could find for information on North American birds relevant to the areas in our game. I ended up with detailed information on, no joke, 750 birds, including links to sound files of their call-outs. Once I handpicked the birds for every habitat in our game, we had to make sure they would sound natural when the player walked around the environment. That meant they had to respond in a natural way to changing circumstances like environment, time of day and weather.

How did you achieve that?
Lucas: We achieved this by turning each ‘virtual bird’ into a little ‘sound robot’ by itself. Each bird sound you hear in Horizon Zero Dawn is actually an interactive sound patch that constantly keeps its eye out for changing circumstances. For instance, when you are in a pine forest, the set of birds available will be different than when you’re in the desert.

The system constantly monitors the environment around you and ‘spawns’ these virtual ‘birds’ (and other fauna) based on what kind of environment it detects around you. So although the animals are virtual, they do have a static location in the world. This means that when you’re turning around, or walking through the environments, they will remain locked to the same location (both horizontally and vertically) in the world. This method works very well within the Platinum Wireless headsets 3D Audio mode, because we don’t fake anything here.

You mentioned fauna – did you do this for flora as well?
Lucas: Absolutely. Take the sound of winds and rains through the trees for example: obviously, rain falling through coniferous trees sounds different from rain falling through pine trees or palm trees. Rain on the leaves will also sound different, depending on whether it’s a few drops of rain or an enormous rain storm. All of those things will respond real time to changing conditions in-game.

How did you prevent the environment audio from clashing with the music?
Lucas: One thing you have to always be aware of when you work with sounds, is that you have a limited amount of frequencies at your disposal. You can’t just throw anything in there and expect everything to be audible. Since I was both responsible for a large part of the environments and for overseeing the music process, it was in my own interest to make sure both would be audible.

Early on, we came up with a concept where music and environmental sounds would give each other their own moments to shine. Sometimes exploration music is full and lush; we use those moment to subtly communicate to the player what time of day it is, what region he or she is in, and just put them in an ‘exploration mood’. Other times the music is very minimal and in the background; at those times you can really hear the details in the environments.

I feel that this concept is responsible for the natural feel you get while walking around in the world – the subtleness of all parts and the full result of the crazy amount of sound voices that are playing at the same time creates an ever changing audio experience.

What about the sounds of Aloy’s movements? How did you go about recording those?
Lucas: We started out with her most neutral Nora costume, and we must have gone through three or four full iterations where we tried to pinpoint the balance between making her sounding unique, strong but also efficient and quiet – because after all, she’s an experienced hunter. Her base costume eventually involved a lot of different materials, like a suede coat, sheets of leather, and wooden beads. Getting the sound of Aloy’s movements right was actually quite labor intensive.

What made it so labour intensive to record Aloy’s movements?
Lucas: Well, every footstep you hear is a combination of a costume sound and a surface material sound, like metal, sand, water, et cetera. We had all those materials available from our Killzone games, but unfortunately the shoes you wear when you record a surface has a big influence on the color of the sound – and the difference between a militaristic boot and a soft-fabric sole shoe is tremendous, so we had to start from scratch. And then we had to do it again when we found out that young Aloy would be walking bare feet.

What about non-walking sounds for Aloy, like swimming?
Lucas: Aloy’s swimming sounds were largely recorded in a swimming pool in Andalusia (Spain), in March, before the tourist season started. A very minimal setup was used: two mics above the water, two mics under water and a mobile recording rig. This all took place during a holiday break. Sound designers frequently take small recording rigs with them when travelling, because those are the times you’re likely to find cool source material for your personal library.

What is your favorite sound in Horizon Zero Dawn?
Lucas: People often ask me that! For me personally, my favorite is not a ‘designed sound’, although it is something that I recorded. When my daughter Laura was only 6 months old, I recorded her vocalisations at home, and they ended up being used for the intro cutscene for Baby Aloy.

Another thing I love is the indistinguishable ‘walla’ voices in the background of the Proving festival – all the people partying, eating, drinking, and sitting around campfires. They were all recorded from developers that actually worked on Horizon Zero Dawn. We got them in one room and turned those recordings into surround tracks, so you can actually walk amongst our colleagues if you use a surround system or the Platinum Wireless headset.

To find out more about the Platinum Wireless headset and its pioneering 3D Audio mode, visit the PlayStation website. To stay up to date on Horizon Zero Dawn and its upcoming DLC, The Frozen Wilds, follow Guerrilla on Twitter and Facebook.