Lots of movies take place in a city. And lots of scenes within these cities take place indoors. In order to convince audiences that they are in a bustling metropolitan area (and not a dead-quiet sound stage), sound editors will cut in city traffic, car honks, planes going by, etc.. Oh yeah, and sirens; lots and lots of sirens. These recordings are typically recorded outdoors, and thus, need filtering such as a high cut, and maybe even a little room verb, to make them match the interior setting. Sometimes you have a scene where you can assume there is an open window, and get away with less filtering, and it sounds totally fine to cut in a recording of an exterior city. Sweet. But for those times when it has been established that there are no windows or it is a well-sealed building, you have to make sure to filter those recordings.
Well, I’ve had enough… I’m sick of filtering!
So I set out to grab some natural sounding interior recordings of the city. I have access to the 14th floor of an office building in the middle of Los Angeles, so I told myself “This will be easy. I’ll just throw a mic up in the room, walk out, scroll through social media for 30 minutes, come back, and presto; perfect recordings will be generated and used for many films to come…”
Oh how naive I was.
Before I get further along into the recording process, let’s first go over the gear I decided to bring along.
I brought with me the Sound Devices 744t as the recorder, as well as the Sound Devices 422 preamp. This combo allows me to record with up to 4 phantom powered mics. As for mics, I brought my trusty Sennheiser MKH40+MKH30 m/s setup as the main pair to record with. Additionally, I packed my much neglected DPA4060 stereo pair (they have been awesome for incognito setups but I find them a bit of a hassle to setup sometimes when compared to my m/s rig). The DPAs came supplied with boundary layer mounts that you can insert the mics into, and I wanted to give them a whirl since I haven’t experimented with that recording technique much, so I plopped them in.
Microphone Placement
I set the m/s rig about an inch away from the glass window. I then taped the boundary layer mics on to the window about 3 feet apart. Zero science or knowledge of boundary layer mics was used for this placement. I am aware that the technique is meant to “focus” on sounds that are hitting the surface, but I figured I’m trying to capture the room, so, this in effect would do the job. I mostly wanted to see how this would sound compared to the m/s rig.
As a side note, I made another recording with the 4060s without the boundary layer mounts, and they did not sound much different. This is likely because I still had them mounted right against the glass surface, and I’ve now come to learn through some minimal research that this will yield a similar effect that the boundary layer mounts give.
The Post Process
Returning to my studio with the recordings, I did the obvious first step in editing which involved removing any and all office noise, which was mostly footsteps, talking, and doors closing. I also noticed right away that the DPAs sounded odd, so I threw up a sound field analyzer to confirm my suspicion that the tracks were out of phase with one another, so I flipped the polarity on one channel to fix the issue. Once I was got along in the edit, I quickly noticed another issue; a “ticking/creaking” noise would randomly occur every 20-30 seconds. I then remembered that while monitoring the recordings in the field, I noticed this sound and figured it was me shifting in my chair, so I exited the room to avoid ruining the recording further… Well, turns out, it seems the building shifting was making the windows creak from time to time (at least, this is my best guess as to what this sound is).
But even weirder than that creaking, which was pretty simple to remove, was what I noticed next…
There was a constant whine in the 1.5K-ish region (with two upper harmonics to boot). At the time of recording, I figured it was distant construction noise of drilling or something else intermittent that I could cut around. But no. This wavering high pitched sound pierced the entire recording. I think it was wind hitting the building and being transferred through the window. I’m not 100% positive what it was. Here, take a listen for yourself:
The Million Dollar Question
This is the point as a sound effects editor where I ask myself the following: is this recording worth the trouble and time to clean up?
If it is an average subject matter (which I consider this to be) intended for my personal collection, the answer is no. I would have likely saved the file but not bothered to clean or catalog it, and instead, go make a better recording. I’ve come to learn that spending exorbitant amounts of time editing/processing a field recording usually means I did a poor job with the crucial first step, and should find a new location to record again.
However, given that I had this blog post in mind, and a number of people had asked me to post samples from the recording, I wasn’t about to scrap this whole project because of this. So, I pushed on with the clean up work to remove the whine.
I used iZotope RX to remove the whine. Using the spectral repair tool, I had to painstakingly go through the entire recording and select the whine (which wavered in pitch, mind you) using the brush tool. The whine had two upper harmonics, but luckily RX has a useful feature to select up to ten harmonics, so that saved me triple the work. After doing this main pass, I had to go through and spot check for little snippets of the whine that escaped my selection, and spectral-repaired those spots as well.
The Finalized Recordings
In the end, I was left with a pretty steady ambience of a building room interior above the city. From the 60 minutes of raw audio, the final processed tracks totaled about 12 minutes of usable ambience. I think this layer will work best as a steady bed, and is ripe for adding even more sweeteners like horns and sirens and such, depending on how busy you want your city to feel. There are some nice vehicle bys, brake squeals, and horns in here for you to utilize when building ambiences for scenes in the city. I’ve trimmed these samples down to about 2 minutes since the full length versions will only be made available in the future Audio Shade sound library (title pending!).
DPA 4060s (Boundary Layer) vs Sennheiser MKH40+MKH30 (Mid-Side)
So, how do the two pairs of mics compare? To be honest, they both sound pretty good to my ears! The bass response on those tiny DPAs still blow me away. They aren’t as insanely sensitive to low end as the MKH series, but they still pack a punch. The DPAs also sound a little more “bright” overall compared to the MKH m/s setup, although, full disclosure, I did indeed roll off some high end on these recordings while processing the files, since it was practically white noise from the room tone, and it did not detract from the definition of the city noise much at all.
Since I am collecting these types of recordings for a library that will essentially be focused around “interior city” sounds, I’m glad I did this research to figure out if it is worth recording with both sets of mics. I’m not convinced either mic pair offers up enough distinction from the other to bother recording with both pairs simultaneously, but I certainly want to do a little more experimenting with the boundary layer mounts before drawing any conclusions.
Stay tuned in the coming weeks for another blog post about my experiences recording ABOVE the city when I got the opportunity to take a ride in a Robinson R-44 helicopter!
As with all blog posts, the sound recordings posted here are available for download and can be used as royalty free sound effects in your personal or commercial projects.