What Actually Makes A City Sound Like A City
You walk down a street and you know immediately where you are. Not from the buildings or the signs. From the noise. There is a layer underneath the traffic and the voices that most people never notice but anyone who has worked in audio design will tell you it is the thing that makes or breaks a soundscape. I spent roughly seven years building urban audio environments for a middleware company before moving into consulting, and the one pattern I keep seeing is that people treat ambient sound as decoration instead of architecture. The name sounds like a meme but it references something real in the industry. Curtis went from recording HVAC systems on Brooklyn fire escapes to building the default atmospheric layers for three major game engines and a handful of VR installations that still get copied today. His approach was simple and slightly annoying in how effective it was. He stopped trying to make city sound interesting and started making it feel inevitable. I learned about his work through a conference talk in 2019 that was more of a workshop than a presentation. He had a single slide showing a frequency graph with three bumps labeled low rumble, mid chatter, high transient. He called it the urban triad. That was it. The rest was just him explaining how most designers pile too many elements into the mid range and create a mud that masks everything else.
The practical method he used involved layering four to six source beds instead of the twelve or fifteen that most teams default to. Each bed occupied a different spectral region. The low bed was usually distant traffic or subway rumble recorded at least half a kilometer away. The mid bed contained human presence without identifiable speech. The high bed picked up the sharp hits. Doors, brakes, distant sirens, construction. These are the elements that sell realism more than anything else. Here is where it gets counter intuitive. Beginners always think adding more detail improves authenticity. It does not. It creates cognitive overload. The human brain filters out redundant information automatically. If you give it too many competing signals, it shuts down and the scene feels flat instead of rich. Curtis would deliberately leave gaps in the mix. Silence between the transients. Space for the listener to project their own expectations into. That empty space is what makes a soundscape feel lived in. I ran into a specific problem last year while building a nighttime district for a virtual production set. The director wanted it to feel like downtown Seattle after rain. My initial pass had seventeen tracks playing simultaneously. HVAC, distant freeway, wet pavement ambience, cafe chatter, dog barks, construction, multiple siren passes, wind through alleys. It sounded like a hospital waiting room. Everyone complained it felt crowded and sterile at the same time. I cut it down to five beds and removed the dog and the wind. The remaining three seconds of silence per minute made the whole thing breathe. The director said it finally felt like a place instead of a recording.
The workaround I ended up using was a technique Curtis mentioned in passing. Instead of relying on the full mix to convey atmosphere, I routed the low bed through a subharmonic synthesizer and only let it activate when the player moved toward busy streets. The rest of the time the low frequencies dropped out completely. This saved processing power and created a dynamic range that mirrored how human hearing actually works. You do not perceive the bass line of a city until you get close to it. There is a hardware consideration worth mentioning. Most people build these environments on headphones first, then transfer to speakers. That flips the balance entirely. Headphones emphasize the mid range and compress the stereo image. What sounds wide and immersive on earbuds will collapse into a narrow blob on PA systems. I now always A/B test urban layers on a pair of nearfield monitors within thirty minutes of finishing a mix pass. It catches problems that headphones hide. If you are starting from zero, do not buy a library pack and start layering. Record your own sources. Even phone recordings work if you are careful. The timbral qualities of a location you have never visited will always feel slightly off compared to something you captured yourself. Two weeks of field recording will give you more usable material than a thousand stock samples because your ears will already know what they sound like together.
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The software side is straightforward. Any DAW with good bus routing will work. I use Reaper with a custom template that splits the mix into three subgroups matching the urban triad. The template has pre-routed compression chains on each band. Low gets gentle knee compression at a 3dB ratio. Mid gets parallel processing to preserve transients. High stays mostly dry except for a deesser on the sibilant elements. This setup takes about twelve minutes to load and then you are mixing instead of building chains. One pitfall that catches everyone is panning. Urban sound does not pan left to right in a linear fashion. It comes from vertical sources as well. A plane overhead, a siren on a highway overpass, HVAC units on rooftops. These need elevation data in spatial audio formats. If you are working in stereo only, you simulate this with high shelf EQ boosts and reverb tails that suggest height. In Dolby Atmos or similar object-based formats, you place those sources above the listener at z-axis coordinates rather than leaving them on the horizontal plane. This is the single most common mistake I see in student projects. Another thing people get wrong is temporal variation. Real cities are not loops. The frequency content changes minute by minute. Traffic density shifts. Construction schedules move. I built a system using procedural generation to stagger the arrival times of transient events. No two siren passes overlap. The ratio of human presence to mechanical noise drifts between 40 and 60 percent depending on a simulated time of day. This adds unpredictability without increasing file size significantly.
The limitations are worth stating clearly. This approach does not work for intimate interiors. The urban triad assumes distance and scale. If you are designing a soundscape for a single room or a small enclosed space, the method collapses. You need different tools. Convolution reverb with real impulse responses from the actual space, close mic sources, and a focus on early reflections rather than long tails. Trying to force city-scale techniques into a bathroom environment will make it sound like the walls are breathing. For anyone on a tight budget, the alternative is to use free field recordings from sites like Freesound and apply the triad method manually. The quality difference between professional field recordings and compressed free samples is noticeable on good equipment but less so on consumer earbuds. If your target audience uses AirPods, the gap narrows significantly. Design for your actual delivery platform, not the one you wish you had. The learning curve is steeper than buying a preset pack. Expect three months of daily experimentation before your mixes stop sounding technically correct but emotionally flat. The difference between a soundscape that works and one that just exists is usually a matter of spectral balance and deliberate silence. Pay attention to what you remove, not just what you add.
There is a community around this work that is surprisingly small. The Discord servers and subreddits are active but the advice quality varies wildly. I recommend focusing on the technical workshops rather than the critique threads. The people posting detailed frequency analyses are usually the ones who have actually shipped projects. The rest are experimenting and being polite about it. If you want to study Curtis specifically, look for the archived stream recordings from his Patreon. They are unedited and often drift into tangents about gear and budget constraints. That is where the useful information lives. The polished conference talks skip the messy details that actually matter when you are down to a seventy-two hour deadline. The industry standard tool chain for this work has not changed much since 2018. Wwise and FMOD remain the primary middleware options. Both support the layering and procedural techniques I described. The learning resources for Wwise are more comprehensive but the community is larger and therefore noisier. FMOD has a smaller footprint and better documentation for indie workflows. Pick one and stick with it for six months before comparing. Switching mid project is the fastest way to waste time.
Field recording advice is the same everywhere. Bring a portable recorder, a pair of omnidirectional mics, and a wind screen even if it is not windy. The budget option is a Zoom H5 with the included capsule. The pro option is a Sound Devices MixPre with external preamps. The difference is in the noise floor and dynamic range. For urban environments, the noise floor matters more than anything else because you are capturing quiet moments between loud events. A recorder that introduces its own hum will ruin a Pass that relied on subtlety. I use a workflow that separates composition from implementation. I build the raw audio in the DAW first, export stems, then import into the middleware for routing and parameterization. This keeps the creative decisions separate from the technical ones. It also makes it easier to hand off to a programmer who does not care about the artistic balance. The middleware becomes the translation layer rather than the creative space. One final practical note. Test your final mix on at least three different playback systems before shipping. Phone speaker, car stereo, and a decent pair of headphones. Each will reveal different problems. The phone speaker will expose muddiness in the low end. The car stereo will exaggerate high frequency harshness. The headphones will hide spatial issues. If it passes all three, it is ready. There is no substitute for listening in the environment where the work will actually be consumed.
