• Sound Isolation and the Perfect Cocktail

    Written by .

    This is the second article in a series: The Essential Guide to Audio for Content Creators. (The previous article was The Science of Sound.)


    Sound as an Awful Liquid

    Let’s imagine sound as a kind of liquid. Unlike any ordinary liquid, this is an extremely messy and spontaneous kind of liquid that appears out of thin air whenever and wherever there’s a vibration. It’s so insistently messy, in fact, that it leaks right through solid walls. It’s so incredibly messy it doesn’t even obey gravity: it just sprays and sloshes and explodes in all directions anytime it appears—which is literally all the time. Where do you usually find it? Well, cars, trucks, and buses pump out huge quantities of it all over the streets and into nearby buildings. All machines do, really. Construction workers might as well be shooting it through fire hoses right into your window. The people upstairs drip it right through your ceiling every time they take a step. The TV in the other room sprays some more of it, arguing neighbors spew it from their mouths, the air conditioner floods your recording space with it, and the computer that you’re working with oozes with it. Every sneeze is a gusher. Don’t even try using headphones.

    Now imagine that amid this chaotic, wet disaster of a world, you’re attempting to mix a perfect cocktail. You’re dealing with precise measurements here, and any foreign liquid entering your glass will ruin the drink—including, of course, that gravity-defying, wall-penetrating liquid that’s being sprayed anywhere and everywhere all the time, getting in your hair and your clothes, etc. Might as well try to mix a cocktail in the shower. Sounds frustrating, doesn’t it?


    So how do you keep this stuff out of your glass? Better yet, how can you keep it out of the room where you’re practicing your mixology?

    Sound Isolation in the Digital Age

    The realistic answer is that you’ll probably have to just deal with imperfect drink-mixing environments. For most content creators, our everyday recording environment (awkwardly moving on from the liquid metaphor) isn’t going to be a dedicated studio that was designed from the ground up for audio. We might be recording in our home, a conference room, a hotel room, maybe somewhere outdoors. And that’s okay. Actually it’s a clear sign that the world of content creation has been democratized. Audio technology has become affordable and accessible enough that almost anyone with a creative vision can produce great-sounding recordings without having to spend a bunch of money booking a professional studio just to use decent equipment—and that’s something truly worth celebrating. On the other hand, the greatest gear in the world won’t change the fact that your makeshift recording space can’t match the acoustic conditions of a high-end studio. That means it’s inevitable that you’ll be faced with some of the disruptive annoyances we mentioned in the last chapter, including sound leakage, outside noise, wind, and unwanted reverberation.

    There are actually two distinct objectives when it comes to troubleshooting these issues. Sound isolation is the effort of keeping the sounds you’re recording within the walls of your recording space while keeping all unwanted noises out of the recording. Acoustic treatment, on the other hand, is the effort of optimizing the conditions of the recording space so that the sounds you’re producing sound the way you want them to. In this chapter we’re focusing on sound isolation. (Some might refer to this as soundproofing, but making a space 100% soundproof—meaning no sound can travel through its walls in either direction—is virtually impossible. So we’ll refrain from using the term here.)

    How Traditional Studios Do It

    So how does sound isolation work? First let’s consider how a professional studio is constructed. Let’s say you had an unlimited budget and the luxury of building a studio from the ground up. What would you do? Basically, you’d build a windowless structure with extra-thick walls of concrete—think a fortress or a bomb shelter. If you were modifying an existing space, on the other hand, you’d achieve the same effect by building out the walls, floors, and ceilings with dense, vibration-absorbing materials such as rockwool and mass-loaded vinyl, bricking up the windows, and sealing up every tiny hole and crack. You might also follow the principle of building a “room within a room,” because leaving a narrow air gap between the new layer of materials and the original layer actually helps prevent vibrations from transferring from one side of the wall to the other.


    But that’s not the end of the job. Because computers, mixing consoles, lights, and recording engineers can all make unwanted noises, a typical pro studio actually has two spaces, which are separated by soundproof glass: the live room, where you’ll find the performers with the microphones, and the control room, which houses the sound engineers, mixing consoles, computers, monitors, etc. And in order to provide climate control and air ventilation to the live room, studios also invest in quieted air conditioning systems with high-quality air ducts. (Talent tends to perform better when oxygenated.)

    I imagine some of you already have your hardhats on and mallets out, ready to smash things and transform your den into Abbey Road. For many others, however, you might already be looking for a way out. We don’t blame you. Even a DIY approach to building out a decent home recording studio can be too daunting a project to people without a lot of time, money, and aptitude for home renovation. That’s why so many people end up skipping the sound isolation step entirely, hoping they can get away with it.

    Reaching for the Attainable

    Here’s the good news if you’re not a musician. Because of the nature of music—its volume, its wider frequency spectrum, its greater reliance on tone and sound quality—it’s fair to say that even though the principles of the music studios described above apply to all kinds of audio, you can probably get away with doing a bit less if you’re primarily recording speech for projects like podcasts and videos—both in terms of isolation and treatment.

    The bad news, however, is that it’s harder than you’d think to get away with doing nothing at all. Thinking of using software noise filters to remove unwanted sounds in post-production? That probably won’t work. Because, by nature, noise filters subtract data from your recording, they’ll inevitably remove some of the sound that you want in the process of removing the noise, degrading your final result. The inadequacy of noise filters isn’t the only concern, either. Even if you’re only dealing with intermittent noises, frequent interruptions that force you to redo takes and edit around noises will end up limiting your creativity—and that’s a big problem, not to mention just a major annoyance. Bottom line: there’s no easy way out of basic isolation practices, even in the digital age. If you want polished-sounding results, you’re probably going to have to do something.

    For the scope of this article, with its focus on content creators, our aim is to help get everyone at least halfway there in terms of sound isolation, rather than setting the bar so high that it scares most people into doing nothing. Fifty percent is infinitely better than zero, and you’ll be glad you got there. So here are some relatively simple, affordable ways to address the weakest links in your recording space so you can set up a halfway decent environment for voice recording. (Of course, we don’t mean to discourage anyone from going a few steps—or a mile—farther if they need or want to. By all means, go for it! The effort will pay off.)

    Common Sense First

    While some of this will seem obvious, the initial steps to sound isolation require no special tools, just some common sense. First, choose the right spot. Unless you live in very tight quarters (not uncommon, of course, if you’re based in New York like Gradus is), there’s a pretty good chance that you might have more than one option when choosing a room for recording. Keep in mind the most common sources of unwanted noise: traffic, appliances, neighbors, air conditioning condensers, and housemates. What’s the most sound-isolated room available to you? It might be a basement, a garage, or a bedroom. Take into consideration windows, the people directly above and below you, and the layout of your building. The less noise you have to deal with right off the bat, the smaller the job you’ll have in front of you.

    The other commonsense step is to remove, shut off, or otherwise silence anything in or near the room that might disrupt your recording. Have a noisy fan or window-mounted air conditioner? Turn it off. Buzzing or humming fluorescent lights? Switch them off and bring in quieter LED or incandescent lighting. An open window? Shut it. A needy dog? Send it out. A noisy fern? Get rid of it. At the end of all this, just stand there and listen for any noises, from the quietest hum to any sudden noises from outside. Where are they coming from? This will give you a good sense of the remaining problem areas that you need to deal with.

    Working in the Closet

    sound-isolation-and-the-perfect-cocktail-closetRemember the idea of the room within a room? Well, chances are that you have a closet in your building that sort of qualifies. Of course it’s far from a perfect option: the walls and doors aren’t particularly thick or insulated, it’s full of clothes and shoes and brooms and who knows what else, and it’s obviously too small—especially if you’re trying to record musical instruments or video.

    But if you’re recording nothing but your own voice, it’s something to have on the table as an option, even if only as a last resort. It’s probably not a viable long-term solution, but it might work in a pinch. As an added bonus, a typical home closet already has some basic elements of effective acoustic treatment, considering its smaller size and its fabric-heavy contents—but we’ll save those principles for the next blog post.

    Blankets, Blankets, Blankets

    Try this. Put on your pajamas and hide beneath the blankets of your bed. You’ll notice that all the noises that are audible from the bedroom are reduced. Likewise, if you were to let out a blood-curdling scream, the sound would be significantly more muffled to people nearby than if you were to scream while standing in the middle of the room. That’s why blankets are actually a chief method of cheap, easy, DIY isolation (and acoustic treatment—more on that later) for many people. It’s far from the most effective solution—and it isn’t the prettiest, either—but for those unable or unwilling to do any home renovation, a layer or three of blankets can sometimes serve as a good-enough approximation of the same principles.

    (You can change back into your daytime clothes now.)

    If you choose to use blankets for sound isolation, however, regular bed sheets won’t cut it. Because a blanket needs to be especially thick and dense to be effective for sound, people typically use moving blankets—the ones that movers use to wrap furniture to prevent damage from bumps and scrapes. You can find these at any home improvement store—but keep in mind that some are more heavy-duty (and thus more effective) than others. For those who want to spend a little more, there are also dedicated acoustic blankets which are sold with a higher price tag. Fundamentally, these are no different from regular moving blankets, though acoustic blankets usually offer clearly stated NRC (noise reduction coefficient) values that let you know exactly how effective they’ll be for sound absorption. (The closer to 1 the value is, the better. Typical moving/acoustic blankets are between 0.3 and 0.5.) In some cases, some of the better acoustic blankets might be a bit more effective than moving blankets, though you can expect to pay handsomely for what will amount to minor performance improvements. A more practical benefit of some dedicated acoustic blankets, however, is that they often come punched with grommets, which is a big convenience if you plan to hang them from hooks.

    So how do you use these blankets? First you’ll want to target your obvious problem areas. Have a computer with loud fan noise? Wrapping the computer directly might cause it to overheat, so try sealing it off from the rest of the room under a desk or other piece of furniture with the blanket draped over like a curtain. If you have noise from a central air conditioner that you can’t turn off, you can use a blanket to cover up the vent in the room. If you have noise entering through a window, hanging blankets over it—multiple layers if necessary—should help to mitigate the problem.

    To hold the blankets in place, you have a couple of options. A more temporary but versatile solution is to use light stands. These aren’t overly expensive (even the cheapest light stands would be good enough to hold a blanket), their max height ranges from six to thirteen feet or so, and they allow you to set up blankets anywhere in the room. Crossbars help with sturdiness, but you can also balance a blanket between two bare light stands if necessary. The biggest benefit of using light stands is that they make it easy for you to control just how much space you’re isolating within a room. If you want, you can build a kind of fort of blankets that encloses just you and a microphone. The smaller the space that you need to isolate, the less work required.

    You can also hang the blankets from the walls or the ceiling, which tends to be more useful if you want to treat an entire room. Clamps (or C47s if you’re a filmmaker) can be used to hang the blankets from existing fixtures. For a more permanent solution, you can install hooks using screws or heavy-duty mounting tape. Note that if it’s possible to hang the blankets with a few inches of separation from the wall rather than directly on the wall, the air gap will make the isolation even more effective. Remember to also cover floors as well as ceilings if you can.

    Tying Up Loose Ends

    It’s possible that you might still have a few nagging sources of noise that we haven’t covered. Is noise leaking through the crack at the bottom of your door, for example? Rather than stuffing something in the crack every time you want to record, you can invest in an automatic door bottom, which seals the gap while still allowing the door to function. And if there are any other small cracks or openings in your walls or ceiling or around your windows, you can plug them up with acoustic sealant.

    Testing Your Results

    Think you’ve done enough? Let’s see what you’ve got. Set up your recording gear and throw on a pair of studio monitor headphones. Start recording. Run through the kind of material that you plan to record, whether it’s speech or music, but don’t forget to also stay silent for a while afterward and let the mic capture the ambience of the room. As you listen critically to the results, you should be able to hear the remaining unwanted noises lingering in the space—maybe sounds you overlooked, whether it’s a low hum from a vent or occasional noises from outside.

    In the end, however, your results probably aren’t going to be perfect. Sound is just too ubiquitous and free-ranging a thing to be effectively sealed out of a space without building the acoustic equivalent of a bomb shelter. But don’t be discouraged! With the affordability of increasingly powerful audio gear and all of the free educational resources and communities available online, people everywhere are successfully making do without the help of a professional studio environment—including some professionals. So once you’ve done all you can (or are willing to do) to isolate your sound, consider it done and move on to the next step, knowing that sometimes you’ll still have to redo a take or edit around noises. There will always be some technical challenges when it comes to the creative process, but as long as you learn from them and continue to refine your approach, you’ll be mixing great cocktails in no time.

    In the next article, we explore some of the most effective and inexpensive solutions for acoustic treatment.

    This post is brought to you by Polsen, Senal, and Auray. These brands are proudly part of Gradus Group.

    Subscribe now to be notified when new articles in this series, new products, and more become available.

  • The Science of Sound (for Content Creators)

    Written by .

    This is the first article in a series: The Essential Guide to Audio for Content Creators.

    polsen-science-of-sound-labcoat Sound is so ubiquitous that we hardly ever think about it—but what is it, exactly? How does it work and behave? Without putting you to sleep with too many details, we’ll cover the essential science behind sound so you’ll understand your medium at its most basic level. Whether you’re an aspiring recording engineer, filmmaker, or podcaster, this knowledge will put you in a better place to learn everything else about the craft of audio recording.

    Making Waves

    In space, no one can hear you vodcast. Forgetting about facehuggers for a minute, this statement is essentially true. If you’re out there floating somewhere between planets, your voice probably won’t be heard. But why?

    When something produces a sound, it’s producing a vibration. For example, your vocal chords vibrate when you speak, just as a drum vibrates when you strike it. That initial vibration agitates the immediate air molecules around it, making the air vibrate. The vibration, traveling through the air the way waves travel through water, radiates from the source of the sound and eventually reaches your eardrums, causing your eardrums to vibrate. That’s when you hear it.


    Outer space, being a vacuum, has no air. When you speak—whether you’re singing, reviewing the latest headphones, or, yes, even screaming—your vibrating vocal chords won’t have any nearby air molecules to transmit those vibrations to your crewmates’ eardrums. No matter how much you strain your pipes trying to get their attention, they won’t hear a thing.



    But let’s assume that you’ll be recording somewhere comfortably far away from any predatorial aliens, whether that’s a studio, your bedroom, outdoors, or somewhere else on Earth. We’ve established that sound travels via vibrations. But how does it move around in a space once it’s airborne?

    Note: There’s plenty more science behind what makes one sound different from another—qualities like volume, pitch, tone, etc.—but we’ll call that extra credit for now. If you’re curious about amplitude, frequency, harmonics, and fundamentals, Google them! A deeper education will only help.

    How Sound Behaves

    When you drop a stone into a pool of water, the resulting waves travel outward in radiating circles. Similarly, sound waves travel in an outwardly radiating sphere from the source of the sound. What happens, then, when it encounters an obstacle?

    One potential consequence is called diffraction. When sound waves encounter obstacles like walls and doorways and objects, the radiating movement allows them to move around those obstacles and continue in new directions. This is why it’s easy to hear a sound that originates on the other side of a doorway or around a corner—like the cooing of an Alien Queen in her chamber guarding her brood.


    Another possible consequence—this one with many implications for audio recording and acoustics—is called reflection. This is when sound waves reflect off surfaces. In certain cases the reflection is heard as an echo. This occurs when the sound is reflected back to the listener with a long enough delay that it seems to repeat the original sound.

    A more common kind of reflection, however, is reverberation. Reverberation occurs when the reflection comes back to the listener with so little delay that it sounds like a prolonging of the sound rather than a repetition. Usually that’s in a room. Remember that sound interacts with everything around you. Unless you’re floating in the sky, that means you’re not only hearing the sound waves that come at you directly from the sound source; you’re also hearing the indirect sound waves after they’ve interacted with and bounced off other nearby objects.

    Of course, even if it doesn’t encounter any obstacle at all, sound doesn’t travel forever. Because sound radiates outward in an expanding sphere, it is spread over an increasingly wide area as it travels. Thus its intensity diminishes according to the inverse square law. In practical terms, that means that each time you double the distance between yourself and the sound source, you’ll hear it at one-quarter of the volume from the previous distance. The takeaway is that the drop-off of sound with distance is pretty dramatic.


    Real-World Challenges

    Drifting off to cryosleep yet? We know this stuff can get a little dry, but hang on for just another minute. Here’s the main takeaway for you as a content creator:

    Sound is not a purely abstract or easily predictable thing. It’s a physical, real-world phenomenon that has some quirks and real limitations that you’ll have to learn to work with.


    That means the sound you want to capture is going to interact with your immediate environment before it enters your microphone, including the walls of your room, your carpet and ceiling, the furniture, the distance to the mic, gusts of wind—even angry neighbors or cranky Xenomorphs. All of these things will have an effect on the sound that you end up capturing, whether they add unwanted reflections or a problem as basic as outside noise.

    And that’s why you can’t just power on an expensive microphone and expect great results. Great sound requires coaxing and finesse, and that doesn’t just mean buying more gear—it means optimizing your recording environment or working around its limitations.

    Now that you understand the fundamentals, let's talk about sound isolation so you can record in peace (and your neighbors stop complaining).

    This post is brought to you by Polsen, Senal and Auray. These brands are proudly part of Gradus Group.

    Subscribe now to be notified when more articles in this series, new products and more become available.