From the acoustics of the room to the instrument and player, from the the microphones you choose to where you place them, a lot goes into a quality recording of an acoustic guitar
From The Recording Guitarist © 2010 by Jon Chappell. Published by Hal Leonard Books, an imprint of Hal Leonard Publishing. Reprinted with permission.
When recording acoustic guitar, you can obtain great results with either dynamic or condenser mics, used singly, in a blend, or in stereo. For acoustic guitars, generally what you hear is what you get. If you use a better mic, you’ll get a better sound simply because the mic is providing a more accurate picture of what’s there. And while it’s true that some mic characteristics are preferable to others for capturing acoustic guitar, the better the guitar sound, the less those factors play into the equation.
Miking Techniques
You can get good results with either condensers or dynamics, but condensers are preferred as they are better able to pick up transients, or the high-frequency artifacts (noise) of the plucked string. A quality dynamic mic like a Sennheiser 421 works very well, though, positioned 18–24 inches away and pointed at the bridge, slightly off axis – as if the “beam” emanating from the top of the pickup were pointed at the 12th fret, and not perpendicular to the guitar’s top. Good miking technique involves nothing more than a lot of trial and error with placement, and then exercising good judgment when you listen to your placements over the monitors.
You’ll often hear people talk about an acoustic guitar’s “sweet spot” – a narrowly defined area where the guitar sounds best. This can be found by plugging one ear and using the other as the mic, pointing it at the guitar while someone plays it and moving around until you find where it sounds good. In this way, you are behaving like a directional mic. Move from fretboard to bridge, upper bout to lower, and vary your distance and angle to the guitar. Your ear doesn’t have the exact “pickup pattern” a mic does, but this can give you a good idea of which area gives you more of the tone you’re looking for.
Room Acoustics
When recording guitar, you should also listen for the quality of the room sound: make sure it has an ambience that makes the guitar sound good. You don’t necessarily need to understand acoustical theory to know when a room is working for you or against you. If things are sounding good in the room, use a mic to capture that quality. If there are harsh echoes and rattling, take steps to cut the room out of the picture.
Acoustic Pickups
Many acoustic guitars, both steel-string and nylon, come with built-in electronics that allow you to plug one end of a normal electric guitar cable into the endpin jack and the other into a guitar amplifier, mixing board, or effects processor. If there are onboard electronics (which include a preamp and EQ), they’re usually found inside the guitar body, with tone and volume controls on the top side of the upper bout.
Pickups are used more and more in live situations, even by the best acoustic guitarists, because of their convenience and manageability. Even in a recording situation, where logistics are not as much of a factor, some engineers and guitarists like the tonal quality of a pickup, and will blend it in with the pure mic sound. One reason for this is because pickups can deliver a more focused bass response than a microphone, and often people will use the pickup of an acoustic guitar to boost its low end while the mic captures the mid and upper frequencies. And of course you can always record just the straight pickup sound (no mic) of the guitar. It’s still unmistakably an acoustic guitar, but it sounds very different from a guitar recorded with just a mic. The sound is described as somewhat “compressed,” “focused,” or “sustained,” and is good for lead lines that need to cut through a busy or noisy mix. There are two types of pickups for acoustic guitars: magnetic and piezo.
Magnetic. A magnetic pickup is most similar to an electric guitar pickup (though it’s optimized for acoustic guitar) in that it uses a coil of wire wrapped around a magnet to capture the vibrating steel strings above it. Since this pickup type is based on magnetic energy, it won’t work on nylon strings. It typically sits in the acoustic’s sound hole.
Piezo. A piezo (pronounced PYE-zoh or pee-AY-tzo) pickup is a thin membrane that’s placed between the saddle (the bone- or ivory-like strip that sits in a slot in the bridge) and the bottom of the bridge. It works not magnetically, but through the varying pressure caused by the vibrating string bearing down on it from above. Contact pickups that adhere to the soundboard are also piezo-based, and some systems have multiple contacts at different points on the soundboard, which are then blended together. Because of recent advancements in piezo technology, the membranes have gotten more sensitive and responsive, and are generally preferred over magnetic pickups for a truer acoustic sound. There are notable holdouts for magnetic pickups, though, including Leo Kottke. And of course, you can always choose one or the other based on the sound you’re looking for or a certain situation.
Combining Pickups with Mics
A potentially negative phenomenon to watch for when playing pickup-equipped acoustic guitars is finger noise. This is the unavoidable skritch the left-hand fingers make when fretting, releasing, and moving along the strings. While this is a natural and listener-tolerated result of playing the guitar, recording guitarists usually try very hard to keep finger noise to a minimum. A pickup tends to give undue prominence to finger noise, because it picks the sound up directly from the string itself, rather than from a distance, as a mic does. Since the mic is some distance away, the musical information (the vibrating string) is usually much louder than the string noise, which is placed in the background. But the pickup tends to give the string noise a bit more “presence,” as though it’s closer to your ear than normal.
One trick that works particularly well in a rock context is to plug an acoustic through a combo amp’s speaker to get an even more compressed, focused sound, and then mic the speaker. You shouldn’t plug straight into the amp’s input, though. A better way is to go into a dedicated mic preamp or even the preamp of your mixer channel’s input. This provides a better match for the two impedances—the output impedance of the piezo and the input impedance of the mic pre. Then, via an aux send, take the acoustic guitar’s signal out of the mixer and run it into the effects return jack of the combo amp, bypassing the preamp stage (because your signal is already preamped). You then have a properly preamped piezo signal run through a nice tube power amp and a midrange-oriented speaker.
This method works well if you’re already in the studio playing an electric through a combo amp and the producer asks you to switch to a direct acoustic sound (and he doesn’t want a miked guitar, as setting up a mic and isolating it isn’t practical). You can have both instruments plugged in simultaneously, and without repatching, switch between the two guitars. Just remember to pull down the fader on the acoustic when you switch to the electric, so that no noise enters through the amp’s effects return jack. This method of using different amp jacks for electric and acoustic guitar works even if you’re not recording via the speaker, but using the slave or Speaker Out of the amp and continuing on to a load box and beyond.
