Fix It in the Mix: All About Mike(s)

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Category: Pulse! Pulse!

July 2021

Last time in “Fix It in the Mix,” I talked a lot about planning a recording session. I’ll talk a bit more about that here, but this installment is mostly about the process of recording itself. I don’t focus too much on precisely where to place the microphone(s) for any given instrument—there are countless sources for the best way to mike, for example, a drum kit or an acoustic guitar (all of which are both right and wrong). This series is more about giving you the most basic tools for translating what you hear in your head into something playable on a stereo. And in this installment I talk about how microphones “hear,” and give you some basic techniques for getting them to give you the sound you want.

The first thing to know about mikes is that they hear differently from human beings. They’re more objective, and far more honest than polite society will generally put up with. Each mike has a pickup pattern, analogous to a loudspeaker’s dispersion pattern. A mike is really just a speaker in reverse. Most mikes have one of three main pickup patterns: omnidirectional, figure-8, and cardioid. Other pickup patterns, such as hypercardioid, are based on these three basic ones.

Omni and cardioid

An omnidirectional mike picks up sound with equal amplitude, regardless of the orientation of the mike diaphragm to the source(s) of sound. A figure-8 mike picks up equally well from the front or back, with nulls to the sides. (Most ribbon mikes are figure-8s.) Diagrammed in two dimensions, the cardioid pickup pattern is, as its name suggests, heart-shaped; visualized in three dimensions, it’s more cherry-shaped, with the mike’s diaphragm pointing into the fruit from the stem. Cardioid mikes pick up sounds well from the front and sides, with a deep null for sounds originating from directly behind the diaphragm. Most mikes found in today’s recording studios are cardioids. All but two of the mikes discussed in the shopping article are cardioid only; those two can be switched to cardioid. Just as with a speaker, a mike’s frequency response will vary with, and within, each pickup pattern.

Figure 8

When positioning non-omnidirectional mikes, you’ll have to take into account the proximity effect: The closer a mike is placed to a sound source, the more bass frequencies below the 200-300Hz range will be boosted. The proximity effect begins to become noticeable when the mike is within about a foot of the sound source, and increases as the mike is moved closer to the source. This is analogous to the bass boost you get from putting speakers next to room boundaries. The amount of bass boost will vary with mike and pattern. An awareness of and judicious use of proximity effect is one way to boost an instrument’s low end without using an equalizer (EQ) during recording, but if you’re not careful it can muddy the sound. If a singer has a tendency to “eat the mike”—i.e., to sing with his or her mouth too close to the vocal mike—placing something between mouth and mike is one way to keep them at the proper distance from each other, to keep your singer from sounding like Darth Vader. A microphone pop screen—a noise filter—is usually best, and provides other benefits I’ll mention later. (It also keeps your mike a lot drier.) If you don’t have a pop screen, bending a wire coat hanger into a circle, stretching a pair of pantyhose over it, and taping it to the mike stand so that the screen is just short of where you want the singer’s mouth, will also work well—unless you’re recording the Beastie Boys, who won’t rock a mike with panty hose. Ever. And if you lack a pop screen, or don’t like what it does to the sound, placing a chair or other object between singer and mike to keep the singer’s mouth the proper distance from the mike will work just as well.

Windscreen

You can’t know how a pair of speakers will sound in your room until you move them in and start playing music through them. The same is true of mikes and the room you’re recording in. You’ll need to experiment with the placements of the mikes, the musicians, and their instruments or amps, to find what works best for each. This can change from song to song—a lot. You might be able to get a drum kit to sound hair-metal huge in an unfinished basement, but is that the right sound for this song? Whether you’re recording in a garage, a basement, or a bedroom, the sound of the room will greatly determine how you mike instruments and voices.

The easiest way to find out how your room(s) and mikes sound is to make recordings and listen to them. This will all be trial and error—there’s no magic formula or shortcut around it—but it will teach you what your room and mikes can and can’t do, and that will make you a better recording engineer. It will also develop your critical listening skills, so you can more quickly identify and adapt to or correct any problems in the sound, and make better mixes and better final recordings. It takes time, but do all of this experimenting before you try to do any serious recording. It will all be worth it—from then on, your recording and engineering will go more smoothly, and it will take you less time to get a better sound.

Once you’re familiar with the sounds of your mikes and room, recording an individual acoustic instrument—say, a guitar, violin, or saxophone—is relatively simple. If the only instruments in a song will be one or two acoustic instruments, recording them in true stereo is a good way to make each stand out and sound more natural. A Blumlein pair of mikes—two figure-8 mikes positioned coincidentally and at horizontal right angles to each other, so that their combined pickup pattern looks like a four-leaf clover when seen from above—is great for pinpoint imaging and natural reverberation. A Blumlein pair works best in a good-sounding room. To get that pinpoint imaging without as much room sound, a coincident pair of cardioid mikes, again with their diaphragms at 90° to each other, works well. This is called XY technique, which means the two mike diaphragms are coincident, though the term is usually reserved for paired cardioids, to avoid confusion with paired Blumleins.

Microphones

Spaced omnis—two omnidirectional mikes spaced a foot or more apart—often produce a sound that’s more natural than coincident techniques, but with less precise imaging. (Can you pick out the third viola in an orchestral recording? Me neither.) Spaced omnis pick up a lot of room sound, so this technique won’t work in all situations, but there are noncoincident stereo techniques (e.g., ORTF, or Office de Radiodiffusion-Télévision Française) that pick up less room sound by using cardioid mikes. In general, noncoincident stereo techniques tend to give less precise imaging than coincident techniques, but make up for it with a more natural sound. After all, the human head contains a spaced array of two mikes—our ears—so it makes sense that noncoincident techniques sound more natural to us. There are even more complex coincident and spaced techniques, such as the Ambisonics mike or a Decca tree, but those are beyond the scope of these articles.

Two things to keep in mind about using true-stereo miking techniques: 1) You’ll need to decide where in the stereo field of the final mix you want each instrument to end up before you begin recording. While you can flip the left and right channels, everything else is locked in place. 2) Recording a lot of stuff separately in stereo can sound really confused and tends to be hard to mix. If you want a stereo recording but don’t want to record everyone at once, lock the mikes in position, then move the players around the mikes to where you want them to appear in the final mix—flipping the left and right channels on one or more instruments but not on all will mess up the sound—you’ll have to plan it all out in advance.

Microphones

Most of your recording will be in multi-mono, with just one mike on each sound source. While most stereo recordings are made with the mikes at a distance of several feet or a lot more—consider orchestral recordings made with just two or three mikes—mono miking an individual source is normally done within a foot of it, including voices. This is called close miking, and here is where the proximity effect comes fully into play. A good close-miked recording is the result of a compromise among the proximity effect, isolation from other sounds, source tonality, and how much of the room you’re trying to capture. Don’t just listen to each mike feed in isolation—listen along with everything else, to hear how it all sounds together. This is especially important for drum kits, which can produce weird (bad) phase effects when many mikes are placed close together. Each mike will, to some extent, also pick up everything else in the room, so make sure there are no problems with tone or phase. Capturing the sound you want with the mike speeds up the mixing process, and generally makes for a better-sounding record because you’ll need less processing in postproduction.

The voice, too, is an acoustic instrument, but it’s usually recorded differently from other instruments. In most music that includes a vocal, it’s the most important and interactive part, which is why it’s usually the last thing recorded. First, as with any other instrument, you’ll want to figure out which mike sounds best on your singer’s voice. Again, knowing your mikes and room(s) will save a ton of time here. Part of the process is finding how close the singer should be to the mike. You can get a more intimate sound and nice, rich bass by singing really close to the mike, but then, on top of the proximity effect, you have to deal with more mouth and breath noises. The worst noises are plosives—hard consonants such as p, t, or b, which can cause a thumping sound when made too loudly and too close to the vocal mike. (Plosives are produced entirely by the tongue, lips, teeth, or glottis—they’re entirely unvoiced, meaning the vocal cords do not need to vibrate to produce them.) Sibilants (s, sh), too, get worse—much worse—the closer the singer’s mouth is to the mike. I’ll talk about removing excess sibilance, or de-essing, in one of my articles on mixing.

Another common way to reduce mouth and breath sounds is to tilt the mike’s diaphragm slightly to one side so that the singer’s puffed-out breath hits the diaphragm at an angle instead of head on. Again, a pop filter is the best way to control most such sounds, but they aren’t 100% effective, and they alter the sound of the voice. I think the pop filter is one of the greatest inventions of recording technology. The foam cover on the Shure SM7 microphone is another type of pop filter, more generally known as a windscreen.

Shure

Next time I’ll talk about using some of the mike techniques mentioned above, and others, to record a primarily electronic solo artist or duo (e.g., Billie Eilish, Daft Punk). I’ll talk about recording individual instruments, but will focus mostly on voices. In the third installment on recording I’ll describe how to record a large group using isolation, overdubbing, and monitor/headphone mixes for the musicians.

. . . Mark Phillips
markp@soundstagenetwork.com