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Three Surefire Techniques
In most cases, you'll want to use a pair of cardioid (unidirectional) mics placed close to the instrument. (For more, see Choosing the Right Mics.) Close-miking -- approximately six to 12 inches from the guitar -- is used in most pop and other contemporary recordings that feature acoustic guitar.
Cardioid mics are generally best used for close-miking guitar because they exhibit less bass proximity effect (or bass boost) than other directional types when placed close to the sound source. And we all know that acoustic guitars can sound boomy if miked incorrectly.
Let's explore three common approaches to stereo miking and acoustic guitar. Each of these techniques has been used on countless hit records. Be sure to check out the corresponding audio links, and of course, consider these as starting points for your own creativity. After you've mastered each one, feel free to experiment with your own variations on each method.
Spaced Pair, Version A
Two mics are placed apart from each other at the same approximate height, one pointing at the 12th fret of the guitar and the other at the bridge.
With this approach -- as with any miking technique that uses two or more mics that are spaced apart from one another -- always be sure to follow the "3-to-1 rule." According to this rule, the distance between two mics
should be at least three times the distance between each mic and the sound source. This keeps phase cancellations to a minimum, resulting in a smoother sound that also translates well to mono. So, for instance, if you've got each mic seven inches from the guitar, the 3-to-1 rule mandates
that you spread the two mics at least 21 inches apart from each other. (One of a few exceptions to the 3-to-1 rule is with the X-Y technique, as described below.)
Spaced Pair, Version B
Our second technique is a variation on the spaced pair. As in the setup above, one mic points to the 12th fret. The second mic, however, is hung from a mic stand at the performer's ear level, pointing down at either the bridge or at the strings just behind the soundhole. For example, if the performer is right-handed, this second mic would be placed over her right shoulder. (Once again, be sure to follow the 3-to-1 rule.)
You can also move this ear-level mic slightly out in front of the performer and angle it back towards the guitar (versus pointing straight down at the floor), for a brighter sound. This technique usually yields a more open -- but thinner -- sound than the simple spaced pair on a horizontal plane. Check out the links to hear the difference.
If you're not getting the sound you want with a spaced pair placement, try moving one or both microphones slightly to improve the timbre. Because spaced pair placement is subject to phase interference, moving one mic only an inch or two can dramatically change the sound. To learn more about how phase affects the timbre of stereo guitar tracks, go to the mono-compatibility link below.
The X-Y Technique
X-Y, or coincident-pair, is the no-brainer approach to stereo miking. If you follow these steps precisely, and are willing to move the mics around a bit to find the sweet spot, you'll find it's hard to make a bad recording. (That's assuming, of course, that your room, your mics, and the instrument -- and, while we're making a checklist, the guitarist -- are half-way decent.)
Place the two mics close together so that their capsules are almost touching. The rear ends of each mic are spread apart at an angle of a roughly 90 to 120 degrees. The result looks like a wide V shape, with one mic's capsule positioned directly above the other.
(The 3-to-1 rule doesn't apply to the X-Y technique because the two capsules are so close that sound waves arrive at both at essentially the same time, minimizing objectionable phase cancellations.)
To start, try placing the two mics opposite the 12th fret of the guitar. If you have a really nice sounding room to record in, try backing the mics up to a distance of one to two feet from the guitar. This will capture more room tone and yield a more natural sound. While the best-sounding position can depend upon the guitar, the room, or the mics, typically, placing the mics around
seven inches in front of the guitar's 12th fret will tend to de-emphasize midrange frequencies. That's because one mic will be pointing in the direction of the bassy soundhole, and the other towards the top of the neck, an area rich in high frequencies.
As you experiment, you'll find that the X-Y miking produces a much narrower stereo image than the spaced-pair techniques. But you'll also hear how X-Y lends a smoother, warmer, and more natural sound to acoustic guitar.
Next Page: Choosing the Right Mics....
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