Vocal Recording Basics Part 3: Frequency Response and Microphones
In Vocal Recording Basics Part 2, I mentioned the use of specific techniques to make the most of audio recording a home or project studio. Those techniques go the furthest in creating a clean sounding recording, and using the right tools takes things just a step further.
Few distinguishing characteristics of microphones matter aside from its frequency response. Frequency response describes how a microphone (or another device) picks up sounds across a range of frequencies. This can get complicated if you let it, but essentially, a professional voice recording sounds best with a microphone that can reproduce a wide range of frequencies. More specifically, vocal recordings sound great with a strong high-frequency response. It just happens that microphones with the highest-frequency responses typically possess strong low-frequency responses as well. That makes these microphones great for recording instruments when needed.
The microphones with the best high-frequency responses are a category of mics called large-diaphragm condensers. Sometimes abbreviated as “LDCs”, large diaphragm condensers use a sensitive, thin membrane in close proximity to a solid metal plate. When sound waves hit the diaphragm, it moves back and forth relative to the solid backplate, changing the distance between the two capacitor plates changes. As a result, the capacitance changes in response to the sound waves. (Source, Neumann).
These sensitive membranes are very sensitive to small changes in air pressure, making them especially sensitive to breathy high frequencies (think “ahh”, “shh”, and “hh”. These mics just give vocal recordings a pristine, je ne sais quoi that’s hard to put into words. Technically speaking, condensers have the widest frequency response of all microphone types. The large, sensitive membrane can capture sounds in a way that’s physically impossible for a phone, stage mic, or other microphone reproduce. It sounds unique, and very noticeable once you know what to listen for. The one microphone I recommend repeatedly is the Audix CX-112B, which costs $299 new, and about $180 used.
Large-Diaphragm Condenser Drawbacks
The one drawback of LDCs come from their ability to capture subtle nuances from a recording. These microphones are omnidirectional in their native state, meaning that they pick up sound from all directions by default. Microphone manufacturers bias most of these microphones to pick up sound unidirectionally (from one direction), but they’re still highly sensitive to noise coming from all directions. These microphones offer poor isolation from noisy environments, which is why they’re rarely seen on stage or other live venues.
Using the techniques from part 2 of this series, however, I still believe that large diaphragm condensers are the best option for general vocal recording. Other microphone designs, such as moving coil (dynamic) mics offer only marginally better isolation with only an extra few decibels of off-axis rejection. Popular microphones like the Shure SM-7B and Electrovoice RE-20 are not only more expensive than the Audix CX-112B, but lack its pristine high-frequency response. Likewise, these microphones are optimized for vocal recording, making them narrowly suited to vocal recording. Unlike LDCs, moving coil microphones make poor choices poor choices for recording guitar, violin, piano or other instruments.
If your recording environment is terribly noisy and you need every advantage to decrease ambient sounds, then, by all means, use a moving coil (dynamic) microphone. Otherwise, use a good large-diaphragm condenser and practice proper recording techniques outlined in part 2.
The second drawback of any condenser microphones is their extreme sensitivity to pops, wind, and handling noise. When purchasing such microphones, it’s wise to invest in a shock mount, or specially designed “cradle” that isolates the microphone from vibrations in the mic stand. If you’re recording in a quiet environment without any floor vibrations, then you’ll likely be fine without one. Think of a shock mount is an insurance policy against rumbling and resonances.
Another important item is a pop-filter or windscreen. Windscreens dramatically attenuate the pops and thumps from plosives, or “p’s”, “b’s” “t’s” and even “s’s”. An experienced user can simply turn his or her head away from the mic slightly during plosive syllables, but amateurs will fail miserably. The best windscreens are made from silk and cost between $30-$60. However, I recommend a windscreen using synthetic fabric since differences are barely noticeable. A $50 silk windscreen only provides a 5% improvement over a $5 windscreen, and your money is better spent elsewhere.
The final drawback to large-diaphragm condenser microphones is that they are… large! When recording sound on camera, these mics are large enough to block most of a person’s face. When addressed close to the lips and combined with a windscreen, then mics take up an enormous amount of screen real estate. There are some smaller LDCs available like the Audix SCX-25, but these are more expensive and lack the high-frequency presence of Audix CX-112Bs.
For professional recording on video, consider the applications of the recording. For anything where the audio is far more important than the visual aesthetics (like a podcast or music performance), use large-diaphragm condensers. For anything else, use a small condenser, handheld mic or a lavaliere. I’ll discuss recording sound for video in more depth in a future article.
Frequency Responses of Other Equipment
Other equipment also requires a strong frequency response for a professional sound, such as your microphone preamplifier, analog-to-digital converters, and even cables. Fortunately, inexpensive recording equipment has had excellent frequency responses since the 2000s. Even if you’re using an older or inexpensive recording setup, rest assured that its frequency response is stellar. Your recording techniques and choice of the microphone will matter far more than the rest of the gear.
Recording a wide frequency response adds a professional, polished element to a vocal recording. Frequency response isn’t as important proper microphone technique, but it adds something noticeable. For general voice recording, use a large-diaphragm condenser microphone like the Audix CX-112B. These microphones are extremely sensitive, so you may need a shock mount and windscreen. If your recording environment possesses a high ambient noise level, then moving coil (dynamic) microphones like the Shure SM-7B and Electrovoice RE-20 may offer a slight improvement in isolation, albeit with a more narrow frequency response. Lastly, the frequency response of the rest of your equipment (or future equipment) is already good enough for a professional vocal recording in the vast majority of instances.
Notes about the Audix CX-112B: Make sure to get the CX-112B, as opposed to the CX-112. The “B” version is tailored slightly more to vocal recording and sounds better on most instruments as well. If the CX-112B is unavailable, the CX-112 is good enough to suffice.
Photos by Eryk Thompson