Let's face it: Vocal recordings often have to take place in less than ideal spaces. It's not uncommon to run into boxiness in small booths, regardless of the microphone. Recently a few Sphere L22 owners have approached us asking if our patented technology could help with that. So in this blog post, we're going to have a close look at what's causing these undesirable colorations and how Sphere can help you optimize the recordings you make in a vocal booth.
The "boxiness" these engineers described is essentially an emphasis of low-mid frequencies and a sort of "ringing" as the sound decays. Even in professional studios with considerable room treatment, these small booths can be a problem. Substantial amounts of EQ and compression, typical in a pop or rock mix, then exacerbate these room colorations and the audibility of the room overall.
In many cases, the issues are most prominent at lower frequencies. This is not too surprising because to effectively treat low frequencies, you need thicker and more expensive absorbing materials.
Most recordists choose a cardioid pattern when recording solo vocals, which makes sense since you generally want to capture what's happening in front of the mic. But the cardioid pickup patterns of large-diaphragm condenser microphones are far from uniform across the frequency spectrum. Towards low frequencies, even some of the most reputable mics become increasingly omni-directional. This effect adds even further to the problem at hand.
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Limitations of Reflection Filters & EQ
Clearly, the ideal answer is to buy high-priced treatment to tame the low end, but the cost for a complete solution might be unacceptable for some. And installation might be impractical due to space or other constraints.
Another cheaper option that people commonly try are reflection filters, such as the Aston Halo or sE Reflexion Filter. These devices can make a difference, but they also color the sound to some degree. Given their size, reflection filters, in fact, lose their effectiveness below about 1kHz. And most filters actually slightly boost room reflections in the 200Hz to 500Hz range.
Some of the Sphere owners I talked to tried varying degrees of EQ to compensate for the low-mid response caused by the room. While they felt there was some improvement, none of them were happy with the results. In the context of a vocal recording, EQ is not going to significantly reduce any "ringing" from the room and at best can just smooth out some broad peaks and dips.
Addressing Room Colorations with Sphere
I wondered if our patented Sphere technology could make a difference since it has very exact pattern adjustment. In all of these cases, we found that by using Off-Axis Correction (OAC) with a hyper-cardioid pattern, we could make a substantial improvement in terms of this boxiness and inaccuracies in the low-mid response.
Download the uncompressed WAV files for easy comparison in your DAW of choice here or check out the SoundCloud playlist below (high-quality monitors or headphones recommended!):
Doing this in Sphere is easy and quick: You need to make sure you are on the "Dual" mode view of the plug-in. Here, enable Off-Axis Correction ("IN" button) on the bottom left, and select a hyper-cardioid pattern as shown below.
As you may know, a hyper-cardioid pattern is more directional than a typical cardioid pattern. Some conventional microphones have a hyper-cardioid setting, such as the venerable 414, but most don't. But for all multi-pattern mics, the frequency response and proximity effect change as you adjust the pattern and results might not always be ideal. Often microphones are optimized to have the best sound when set to cardioid. But Sphere with Off-Axis Correction doesn't have this limitation. When you enable OAC, you will always achieve an ideal polar pattern, no matter which mic model you select.
Off-Axis Correction also has "On Distance" and "Off Distance" controls. Usually, the default settings (as shown above) work well so you can leave those settings alone if you prefer.
The "On Distance" setting corresponds to the distance between the sound source and the Sphere microphone and should be set accordingly. The "Off Distance" adjusts the off-axis distance, which corresponds to approximate the distance from the microphone to the booth walls. But it's fine to adjust these controls by ear.
With the accurate and precise pattern adjustment that Sphere is capable of, it also becomes possible to more strategically place the room treatment just in areas of maximum pickup. For a hypercardioid pattern extra treatment can be placed directly behind the mic to minimize pickup from the rear lobe. And it's generally a good idea to place treatment directly in front of the mic (behind the vocalist) since that is the area of highest sensitivity.
While Sphere is not a panacea for room issues, I think you'll agree that it can make a considerable difference. Combined with decent room treatment, the results can be truly professional.
Identifying Room Problems with Sphere
Sphere also allows one to better diagnose problems with the room. This can be done by comparing the frequency response of the rear pickup, which is mostly reflected sound, with the front pickup, which is primarily direct sound.
To do this, process the audio (a vocal track or whatever you want to record) using Sphere 180 with Off-Axis Correction enabled and set to cardioid. Then using a DAW or plug-in with frequency analysis, you can see what frequencies are too pronounced in the reflected sound (Need a free spectrum analyzer? I like SPAN by Voxengo or MAnalyzer by Melda Production. Both are reliable and work across all plug-in platforms).
It can also be helpful to listen to the rear output of the microphone. Ideally, the sound should be pleasant and not overly colored or comb filtered. To do this just press the SOLO button for "R" output in Sphere 180, or click the ‘REV’ button in the regular (mono) Sphere plug-in.
Shown here is a vocal recording example in a room that still has too much reverberation below about 500 Hz. The cyan curve is the front side of the capsule, and the magenta is the rear side. Ideally, the frequency response of the backside should track the one from the front, but with a considerably lower level.
Here's an example of a room that is very well treated. You can see how the reverberant sound is a lot quieter than the on-axis sound across the entire frequency spectrum.
It's always best to start with a well-treated room but ultimately you need to make work whatever environment you might have. Especially for those of you who record in green rooms, hotel suites, and tour busses, room treatment is simply not an option. In addition to giving you a plethora of sonic options, Sphere can help you achieve better recordings in small rooms. I hope this blog post on optimizing your vocal booth with Sphere proves helpful to you.
With Sphere, you can audition and change the microphone model both while you're recording but also long after tracking. This makes comparing microphones really easy and means that you don't have to commit right away. We have ready-to-go session files available for you with several acoustic guitar examples so you can experiment on your own. You are invited to install the free, fully-featured Sphere plug-in for all major platforms and DAWs. Try it now and reimagine our library of pre-recorded tracks.