Small steps towards better recorded sound quality - pt. 1: Optimize your environment
Updated: Mar 12, 2021
Opera recordings are never true to life.
Even the best professional equipment in an optimized hall cannot capture the true sound of live opera. So how are we supposed to get decent-sounding recordings on our own with limited equipment in our homes, apartments, churches, practice spaces, etc.?
First things first: temper your expectations. Your recordings, whether professionally engineered or homemade, are limited to the quality of the equipment and the environment in which they are made. Technology, for all of its advances, is not up to the task of capturing the operatic voice in all of its true glory, but there are some steps you can take to ensure you can get functional sound quality for your recording needs. There are no silver bullets for great quality audio at home, as every voice, every room, every recording device, etc. is different. Experimentation will be required to optimize your recording setup to suit your individual needs. I highly recommend doing this experimentation well in advance, so you are not scrambling to find a good setup the day of your recording.
Part one of this series will focus on optimizing your recording environment. Environment is the first, and perhaps most crucial, link in your audio signal chain. The space you sing in shapes your sound, and even the most expensive microphones and equipment will sound bad in a room that is not optimized for acoustic quality.
The first thing you should know is that sound reflects. Think about shining a flashlight directly in to a mirror. The light reflects back and shines on the opposite wall, right? Sound works much in the same way. If you sing in the direction of a hard surface, the sound wave can't penetrate very far in to the surface, so the sound bounces off of the hard surface and then reflects off of the opposite surface, and then back to the original surface, back and forth, back and forth, decaying until it dies away entirely. This is what creates an echo. The farther away reflection surfaces are from one-another, the greater the delay will be in reflection, making the echo more pronounced to our ears.
In a square/rectangular room, there are 3 reflection patterns: front to back wall, side wall to side wall, and floor to ceiling. As opera singers, we have trained our voices to create very direct, loud sounds to cut through an orchestra and chorus in a large hall (I will not get in to fundamental frequencies here, but if you are interested in dipping your toes in to the subject, this brief explanation from Scientific American is a good place to start). These direct sounds are not optimal for recording, because the direct sound and direct reflection of that sound is very harsh, especially in close proximity. The smaller the cubic volume of your space, the less time there is between reflections, or reverberations of sound, giving the ear (or the microphone, in this case), less time to process the full spectrum of sound and resulting in a harsher, less warm-sounding recording. Large spaces with 3 reflection patterns (think of yelling in an empty warehouse or church space) are also not ideal, because the large delay in reflection causes a cacophony of sound or flutter echo that can last several seconds and interfere with with the clarity of the sound.
Additionally, every room is going to have its own dominant tones, known as its "room mode," based on the particular size and shape of the room (think about a wine glass that resonates at a certain pitch when you tap it). No matter how good your recording equipment is, the room will enhance its dominant tones, and that is what the recording will pick up the most, influencing what you hear by making some frequencies louder and cancelling others out. You can adjust your room mode by treating for acoustics.
There are two ways you can treat your room for better sound: absorption and diffusion.
We'll start with absorption.
Sound waves are energy. Hard surfaces are not efficient at absorbing this energy, so most of this energy gets reflected back at the source. But when a sound wave hits an absorbent material, the material allows the sound wave to pass through, meaning less of that sound energy will reflect. Having some sound absorption is important to prevent all of your reflected sound from hitting the microphone. The best place for sound absorption in a room is behind the sound source. A king-sized duvet hung on the wall behind you (or better yet, a few inches out from the wall) is actually quite effective at sound absorption, though it does not make for the best visual aesthetic in a recording video. Heavy curtains also offer some sound absorption, and the aesthetic value is higher than a large blanket hanging behind you, though they are less effective than that duvet, because they are not as thick.
Acoustic foam and sound panels are designed specifically for the purpose of absorption by creating a porous surface for the sound to move through and slow by way of friction (if you recall the first law of thermodynamics from high school physics, energy is a constant, so it cannot be created or destroyed, but it can change state. In the case of sound waves passing through an absorber, the friction changes the state of energy into heat, which reduces the intensity and strength of the sound waves. Rub your hands together and feel them warm up. It's the same principle at work). Acoustic panels can get expensive unless you have the know-how and means to DIY them (that's another blog post for another time, but here is a good place to start, if you're interested).
A cheaper and better-looking option are these wall tiles that I use in my own home studio. However, you need a lot of these tiles to cover a large surface. They are not as effective at absorbing sounds as acoustic foam, because they are not as dense, and they are mounted directly to the wall, so there is no air gap behind them. I have interspersed mine with cork tiles for an extra kick of sound-absorption. Cork is one of the best sound-absorbing materials you can find; just 3mm of cork can absorb up to 10 dB of sound. On top of that, cork boards are easy to find and extremely cheap. I even found cork tiles to match my hexagonal sound tiles at Target. These are a great option for apartment dwellers, because they can be attached to the wall with double-sided 3M adhesive that can be removed without damaging the wall. Note: sound panels are most effective for high and mid-frequency absorption, but do not work well with bass frequencies. Bass traps are important to consider, but I will cover those when I share a sound panel DIY in the future.
Sound absorbing alone will not create an optimized sound for recording opera. Think about singing in a sound-proofed practice room. That is never a pleasant experience, as we are robbed of most of our acoustic feedback. A lot of sound studios are heavily absorbent spaces, designed to isolate the instruments as much as possible, and reverb is added back in during post-production. If you find yourself in a sound studio that is all about isolation and absorption, turn the other way and run. This is not the place for you.
In order to optimize the acoustic sound of our voices, we also need sound diffusion. In fact, proper diffusion alone will give you better results than proper absorption alone (of course, having both is the ideal). Diffusion is something our concert halls are designed to do. Think back to your rectangular room with its 3 points of reverberation. These 3 points can be heard in a recording, creating a sense of localization. The sound waves are concentrated, moving in the same direction at the same time and come back to you at the same time. In short, you can hear the shape and size of the room. Now think about a concert hall. It is probably full of irregular, non-parallel surfaces and panels hanging from the ceilings and mounted on the walls. Those shapes and panels are not just aesthetically pleasing; they are specifically designed and placed to create diffusion.
A diffuser scatters the sound wave reflections along different paths, not just the direct path created by a flat surface like your wall. A good diffuser is designed to scatter the waves evenly in all directions. Because of this, some waves have to take longer paths to get back to the listener. Instead of one concentrated wave of sound reflection hitting the listener (or the microphone) at once, we have numerous waves that take different paths and hit the listener at slightly different times. The sound is no longer localized, and the waves hit our ears at different times with different intensities based on how much they have decayed over the time and path they have traveled. The net result is that the room sounds larger than it is, and a greater spectrum of sound is perceived. This is also how large concert halls sound resonant but not "echo-y." Doesn't that sound like what we're aiming for in a good recording?
Unfortunately, diffusers need to be much more precise than absorbers to be properly effective. Trying to diffuse sound with household objects, such as books placed at different angles around the room, could actually hurt more than help, because you have no idea which frequencies you are diffusing and which you are not. You could certainly experiment with different diffusion surfaces until you find something that sounds good, but that is not a very precise experiment, and you'd have to make sure you place the exact objects in the exact places at the exact angles every time to re-create the sound.
The most effective diffusion panels are called QRD, or quadratic residue diffusers. QRDs employ a series of mathematically-calculated wells of varying depths. These are set in a sequence based on prime root numbers to diffuse energy equally. If your eyes crossed reading that, don't worry. You don't have to understand them to know that they work.
There are a lot of DIY plans for QRDs out there, or you can purchase pre-made panels from sellers on Etsy, though they tend to get expensive.
Another popular design is called a skyline diffuser, and you've probably seen one of these before and mistaken it for abstract wall art.
Skyline diffusers are slightly less effective than QRDs, but they are much better than no diffusion at all. They also tend to be heavy and need to be mounted directly in to studs, which may not be an option for apartment-dwellers. On the plus side, they are very easy to DIY, if you have the proper tools.
In the end, a diffuser is going to be an investment, either in time or money, but if you plan on making recordings in your space long-term, a diffuser is the most effective way to tune your space and assure better sound quality in pre-production.
Before you begin recording at home, take some time to mess around with the acoustics in your space using a combination of absorbing and diffusing. It won't be an exact science, unless you make the major investment in panels meant for your specific frequencies and room mode, but any improvement you can make in pre-production will yield a much better sound in post-production.
In the next part of this series, we will talk about different types of microphones. Also, if you haven't read it yet, check out my post about optimizing your video quality.