Subjecting the mysteries of beauty to cold, bloodless scrutiny often invites disillusionment. Take your favorite acoustic guitar, for example. Played in the open air, it can caress your ears with a beatific timbre that inspires songs, melodies, and even inner peace. But point a microphone at your old friend, and strange things can happen. The combination of mic coloration, signal chain anomalies, and room acoustics can transform your flat-top’s once-shimmering highs into piercing clangs that sound like the rattling chains of Marley’s ghost. In addition, the guitar’s inviting warmth can degenerate into an aggressive, booming low end, and fret buzzes and string squeaks can wail like a World War II Stuka blitzkrieg.
Of course, you can always get lucky and capture a wonderful tone the first time you set up a microphone, but here are a few basic tricks and techniques for those times when luck is partying with someone else. Keep in mind that recording is often a creative science, rather than an exact one, and that experimentation and outright foolishness can produce brilliant results. In addition, you must start with a good-sounding instrument. When faced with a thin, buzzy acoustic guitar, for example, even the most expensive microphones, preamps, and signal processors can only endeavor to record a bad sound exceptionally well.
The recording environment will affect the quality of the source sound—your guitar. A typical bedroom studio—inhabited with plush bedding, thick curtains, and wall-to-wall carpeting produces a very dry room tone that can suck the shimmer out of even the most sparkling acoustic. On the other hand, a small, tiled bathroom often produces spiky signal reflections that can mix gnarly slapbacks, annoying flutter echoes, and clattering treble frequencies with the source sound.
Obviously, most home-studio buffs can’t afford to build acoustically marvelous rooms. But you can be a tad more finicky about where you record your acoustic guitar tracks. Play your guitar in every room in your house, and listen critically to determine where the tone sounds best. And don’t forget to audition stairwells, walk-in closets, enclosed patios, (unfilled) bathtubs, and other suitably bizarre nooks. The reason for this exercise is to document the different sonic personalities available in your house. While you’ll most frequently choose to record in the space you’ve marked as “best,” at some point, a strange, spiky, or boomy environment may produce better tonal options for a particular track.
If you’re stuck with a bunch of recording spaces that sound just plain funky, you can try “tuning” the room acoustics. For example, if a room is so dead that it causes your guitar to sound limp and boring, scatter reflective surfaces around the mic positions [Fig. 1]. You can even counteract the sound-deadening characteristics of carpet by laying down square sheets of 1/2" plywood.
Conversely, if an extremely live environment is drowning tones in an ambient wash, tame the signal reflections by enclosing the mic position in a web of soft, absorptive items such as blankets and throw pillows. Pro studios often use specially designed panels [Fig. 2] to “shrink” an acoustical space into a less ambient environment, but a little ingenuity can often turn household goods into surprisingly workable sound absorbers. Try standing a mattress on its side, and leaning it against a wall, or draping thick blankets over a few chairs. Now you can simply move the objects around until the acoustical problems are diminished, or until you hear the desired combination of source sound and room ambience.
Once you’ve identified the timbral colors that are attainable acoustically, you can start auditioning a critical electronic tool—the microphone. The acoustic guitar—much like the human voice—is a very dynamic instrument that produces an abundance of tonal shadings, and it’s critical that the microphone is up to the task of reproducing every sonic nuance. To this end, your “matchmaking” should involve trying a number of different mics to see which one best captures the instrument’s tone. This is a good time to contact friends who may own some cool mics that you don’t own yourself. If the “mic collective” option is not possible, consider renting two or three pro-quality microphones from a local studio-rental outfit.
Which type of mics are the hippest? Well, condensers are pretty much the hands-down winners. These mics typically possess the sensitivity, frequency response, dynamic range, and mystic vibe factor to capture all the glories of an acoustic guitar’s chime and luster. Large-diaphragm models offer a wide tonal range, with robust lows and shimmering highs, while small-diaphragm models tend to accentuate the mid and high frequencies. Dynamic mics—such as the venerable Shure SM57—can certainly do a fine job, too, but most dynamics fail to deliver the airy, dimensional quality of a good condenser.
Ultimately, the mics you choose, and how you place them in relation to the source sound determines the lion’s share of the recorded timbre. Therefore, be sure to allow yourself the time to really experiment with mic positions. If it takes an hour or so to discover a fantastic sound, so be it. The following mic-placement techniques should help you get started.
Monaural miking. Having only one mic available is not a tragedy—you can still capture an exquisite tone if you find the guitar’s “sweet spot.” If you want to accentuate the instrument’s high-end sheen, place a condenser approximately 10" from the face of the guitar, pointing at the 12th fret [Fig. 3]. To add some low end—or to balance the relationship between bass and treble frequencies—aim the mic at the bottom of the soundhole, near the bridge. Be sure that the mic capsule is not pointing directly at the soundhole, however, because the airflow can cause “woofs” and/or flabby bass. To minimize the boom, simply turn the mic until it is at a 45° angle to the top of the guitar. Now the air rush will not hit the mic capsule dead on.
Switching a multi-pattern condenser mic to its cardioid pattern can minimize room reflections and produce a sharp, articulate jangle. For a more ambient perspective, select the omnidirectional pattern, as it lets the mic “hear” everything within a 360° radius.
Stereo miking. To produce a more expansive tonal spectrum, use a large-diaphragm condenser to record the low-end resonance of the acoustic, and a small-diaphragm condenser to pick up the guitar’s high-end sparkle. Position the large-diaphragm mic approximately 6" over the bridge, and angled towards the bottom of the soundhole. The small-diaphragm mic should be placed 4" to 8" from the neck, aiming at the 12th fret. Both mics should be switched to their cardioid patterns to ensure that the stereo perspective is preserved. (Omnidirectional patterns can smear the articulation of the right/left sound field by recording too much room ambience.)
While some professional engineers prefer to use matched mic pairs (same manufacturer and model) to capture a balanced and natural picture of the source sound, an unmatched pair can be used to further emphasize the timbral differences between the guitar’s high and low end [Fig. 4].
Go For It!
These are basic strategies for documenting the beauty of your favorite acoustic. Hopefully, they will not only help you record excellent tones, but also trigger experimentation. I’ve often found it’s the “wrong” techniques that deliver the most stunning results. Trust your ears, and you’ll be fine. (And if you want to learn more about audio production, check out our marvelous family member, EQ magazine.)