The sound of plucked-string acoustic instruments, from the mandolin to the ghimbri, has enlivened thousands of recordings in nearly every genre of music since the invention of the gramophone. The acoustic guitar enjoys the most prominent and ubiquitous presence of them all, particularly in Western classical and popular forms, possessing an organic, soulful quality and texture that adds an insistently human dimension to any mix, whether as a solo or ensemble instrument.
In this article we'll discuss microphone placement, and other relevant recording techniques used in commercial studios to cut a successful acoustic guitar track, and apply them to the less formal home or project studio setup.
Prior to recording the instrument, change the strings - ideally the night before the session. This will allow the string tension and tuning to adjust and settle in. The guitar will speak with a full, bright clarity, allowing the performer to fully concentrate and co-operate during the microphone setup process. Always have a tuner within reach, and check the tuning on a regular basis (after every take, if necessary) depending on how well the guitar retains its tuning.
The gauge, or thickness and weight of the strings, is entirely up to the performer.
While heavier-gauge strings will generally help produce a fuller tone and more sustain, sound is always second to performance, and the performance of someone unused to playing heavier strings will not benefit at all from a last-minute change, regardless of the sound.
The guitar should be set up so there is null or minimal string buzz; this type of noise is distracting, detracts from the performance, and cannot be fixed in the mix. Guitars, like cars, require a degree of regular maintenance, so don't underestimate the value of a professional setup and adjustment.
Finger noise is another potentially distracting problem associated with acoustic guitar recording, easily solved by a variety of fingerboard lubricants available at any music store. Keep a can or bottle handy in the studio, and apply liberally if you hear consistent squeaks and groans emanating from the guitar as the performer slides up and down the neck during sound-check. Several string manufacturers offer a variety of strings that are coated with different polymer compounds, greatly reducing string noise, as well.
Finally, don't forget to make sure the boom attachments on your microphone stands are in good working order. A perfectly-positioned microphone is useless if the stand can't support it, and a great sound is often an inch away from a dead zone.
Mics and Positions
In general, an acoustic guitar's string tone emanates from the bridge to the near rim of the soundhole. Low end richness is produced where the neck joins the body, and the boomy, often unpleasant low end comes directly from the center of the soundhole. The ear perceives this naturally as you position the pick in different areas. The clearest, most balanced sound is usually produced by strumming or picking near or on the far rim of the soundhole that faces the bridge.
Some engineers use their ears exclusively, listening for the best spot and pointing the microphone(s) accordingly. Others use headphones (a headphone extension cord is usually a must, even for smaller recording spaces) and move the mic around like a stethoscope to find the best position. Wherever the guitar sounds best is the right place, frankly.
All the techniques we'll discuss apply equally well to both classical nylon-stringed and 6- or 12-string steel-stringed guitars.
Whether the guitar is meant to be recorded as a solo instrument, or as part of an electric or acoustic ensemble will often determine whether a mono or stereo miking approach is taken, depending on the size and color of the instrument that you're trying to capture in the track. Production considerations usually precede the actual recording process, and the technical choices usually follow the lead of the musical arrangement.
Mic Selection on the Job
Many engineers prefer small-diaphragm condenser microphones for recording an acoustic guitar. These condensers tend to respond well in close-miking situations to the natural transient response and dynamic character of the instrument, reproducing the sound with better clarity, sparkle and detail than their large-diaphragm brethren, with minimal distortion and coloration.
On the other hand, you can't beat the breadth, air and expanse of a good large-diaphragm, particularly if you'd like a bit of room sound in the recording, and want to place the mic a few feet or more from the source. I've had very good results using one of each, at a variety of distances and angles. The small-diaphragm (set to a cardioid pattern, 6-8") is usually facing the 12th fret or further up on the neck, and the large-diaphragm (cardioid or omni, 8"- 3') sounds good pointing toward the bridge or a little past, angled toward the outer rim of the soundhole that faces the bridge. This combination of mics yields brightness, fullness and manageable room sound, and works well if you want some size to the instrument in more isolated, intimate musical passages. It also folds well to mono, as long as you keep your ears open for phasing problems and make use of the phase button on your preamp or mixer!
Let's discuss phase cancellation and the 3-to-1 rule for spaced pairs and other multiple- microphone applications. Phase problems occur when sound waves from the same source arrive at the microphones at different times, at different points in the 360° wave cycle, according to the mic's distance from the source. Phase cancellation will result in either partial to complete loss of signal, or severely degraded frequency content.
The 3-to-1 rule is good preventive medicine and works like this: The distance between 2 microphones should be 3 times the distance of each mic from the sound source. Thus 2 microphones 8" from the guitar should be 24" from each other. This technique is a big help, but always check phase either way; a flip of the phase invert switch on the offending mic channel will often do the trick.
Another technique that works with mic pairs, whether mixed or matched, involves a single overhead (actually over the right shoulder, at ear-level) mic positioned over the guitar body, and aiming down toward the floor at the bridge or string area behind the sound hole. The other mic is positioned in front of the body, aimed at the 12th fret. Moving the overhead mic further forward and away from the instrument, angled back at the same bridge area, will create a somewhat brighter, but thinner tone. In a way, this placement mirrors what the performer hears (if he or she is left-handed, the positioning is reversed), but be sure to allow for maximum comfort and minimal intrusion. Engineers sometimes forget the inhibiting factor that can accompany being surrounded by microphones and stands, so make sure the performer has plenty of room to play properly, as again, performance comes first.
If you're limited to only one microphone, a close-positioned (6-10"), small-diaphragm cardioid condenser is probably your best choice for acoustic guitar applications, particularly in dense ensemble arrangements where more brightness and detailing may be required for the instrument to cut through. Double-tracked rhythm and arpeggio parts, hard-panned left-right, sound huge and really glisten. It's a great trick if you want a big stereo spread and size from one microphone.
Adventures in Stereo
There are many stereo miking techniques used in the studio. For the purpose of recording the acoustic guitar in the home or project studio domain, there are 3 setups that work well for stereo imaging: X-Y, ORTF, and A-B stereo. Solo acoustic guitars sound excellent using these techniques.
The X-Y setup entails 2 coincident small-diaphragm cardioid condenser mics arranged in a V-shape at a 90° angle, with the capsules on top of each other, almost touching. Position them at or around the 12th fret at a distance of anywhere from 8-24", and you'll achieve a pleasing, balanced tone from the instrument, blended with some room ambience, very natural and usable. The 3-in-1 rule is not a concern with this application because the capsules are so close; the sound arrives at the mics almost simultaneously.The X-Y stereo image is rather narrow, so if you'd like to create a bigger guitar, try an ORTF setup, a stereo configuration (also known as a spaced X-Y) involving 2 small-diaphragm cardioid (or omni) condensers spaced roughly 7" apart (6.75" for the fanatics) with a 110-120° angle between the capsules, basically a wider, mirror-image, V-shaped variation of the X-Y. ORTF, and its own variants, DIN and NOS (90° capsule angles but spaced roughly 8" and 12" apart, respectively), are not as safe a bet when folding to mono as X-Y, but offer a bigger, more gracious stereo image and tone. Check your phase!
Finally, there is the A-B spaced-pair, which utilizes 2 cardioid condensers placed at roughly the same height, aiming at the bridge and 12th fret areas of the instrument. The 3-to-1 rule is in effect here, strictly enforced! This technique is the most flexible, and requires the most aural concentration, but will yield some large, smooth, balanced results that translate well to mono as well, for a big, frequency-rich sound that also works well for double-tracking.
Tricks and Tips
Recording is art and science, and the mic techniques mentioned above represent the tried-and-true in both my personal experience and that of others. A well-tuned, well-maintained instrument will always be easier to record in general, and hopefully mastery of these techniques will help speed up the process and reduce fatigue for both performer and engineer. Never ignore the happy accident - if it sounds good, press record!
We've not addressed the issue of room sound, partly because the average house or apartment may not offer the optimal qualities of ambient spaces found in the better commercial facilities. This is why we've mostly discussed close-miking techniques that minimize room sound.
That being said, if you use a set of headphones, and poke a mic around your space while the guitarist is playing, you'll probably find some surprisingly good, useful reflective areas for situating either the player or an ambient mic. Extended-length microphone cables, and a headphone extension cable or two, will allow you to explore areas of your abode outside of the recording space for special ambiences.
Don't underestimate the reflective value of doors, mirrors, un-adorned wall surfaces, hallways, and bathrooms. Many compelling effects may be achieved on a recording with the creative use of room ambience, so take a tour of your dwelling some time with that in mind. You'll be amazed.
As for using EQ and compression signal processing while recording, the less the better. You should be able to get a good sound from a good instrument and a good performance using the microphone and your ears. Recorded compression or EQ cannot be removed, but both may be added during mixdown to enhance the guitar sound within the track.
Good luck to you all, and don't be afraid to move that mic around! That's where it all starts.
Featured: 2003 TD-R Custom, Huss and Dalton Guitar Company, Staunton, VA
Very helpful article, thank you so much!
The 3 to 1 rule does not apply to stereo recording of a single sound source (here an acoustic guitar). It comes into play when recording separate sound sources (say two singers). It would be best to remove that part of your article to avoid confusion to those starting out to record their guitar.
Actually it does not apply to stereo recording of a single guitar and it is not helpful to indicate that it does. A topic for forum discussion perhaps to discuss why this is.
Actually, the 3 to 1 rule does apply here, as the subject is phase cacellation (due to sound from a single source arriving at each of the 2 mics at slightly different times); not isolation of separate sound sources, as with 2 singers.
very good, useful, timeless information.....thank you.
Great article-good nuts-n-bolts stuff!Thx