Many factors can influence the recording of the acoustic guitar. This can make it very challenging and often results in a one-dimensional mix. This article will detail three microphone techniques that are most commonly used in recording acoustic and electro-acoustic guitars, and will outline some key factors that may influence the recording.

Preparation

Before any recording takes place ity is advisable to have the instrument operating in full working order.

- New strings can give a brighter sound, which is better than over-compensating with EQ. - It is also important that the instrument is not making any buzzing noises when played. - Also check all cables and connectors.

Room acoustics can also play a key role in getting a good recording. You can get great results when recording in a nice live environment, with not too much high frequency absorption. When there is a lack of natural reverberation, the recording will suffer and may sound dull. It can help to record near reflective surfaces such as windows, wood or other hard surface areas.

Microphone Technique

Recording in stereo using a matching pair of microphones can add depth and more definition to the recording. If you compare any stereo technique with, for example, a single microphone technique, you will notice a more full-bodied sound with stereo. This will stand out more when recording multiple instruments.

Phase Cancellation

Phase cancellation develops when two or more microphones pick up the same sound at different arrival times. When the suignals are mixed, there will be undesirable dips and peaks in frequency response.

Spaced Pair Stereo Technique

Both microphones are positioned at the same distance from the sound source. One microphone points towards the bridge of the guitar and the other microphone points towards the twelth fret. The microphones can be placed about twelve inches away from the instrument while still observing the 3-to-1 rule. Again it is good to experiment with microphone positioning; moving them further away will create more ambience. Figure 1 shows two space pair methods.

Three Surefire Techniques

In most cases, you'll want to use a pair of cardioid (unidirectional) mics placed close to the instrument. 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 approached to stereo miking and acoustic guitar. Each of these techniques has been used on countless hit records.

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 towards 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.

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 interferance, moving one mic only an inch or two can dramatically change the sound.

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 od each mic are spread apart at an angle of roughly 90 to 120 degrees. The result looks like a 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, minimising 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-emphasise midrange frequencies. That's because one mic will be pointing in the direction of the bassy soundhole, andf 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 the acoustic guitar.

Choice of Microphone - Microphone Type

Condenser type microphones are often used for acoustic instruments. Most dynamics will not capture enough detail and clarity because of their limited frequency response. Most engineers use large-diaphragm condensers and these are arguably the best choice because of their ability ot capture the wide frequency content of the acoustic instrument. Large-diaphragm condenser microphones will need phantom power. Small-diaphragm condensers are also available, and can be battery powered, which makes it very convenient if a more mobile approach it recording is neccessary. Small diaphragms offer a better transient response than their larger cousins and can exhibit a more detailed sound.

Summary

Stereo microphone techniques capture a sound event in its entirety, as well as conveying a sense of spaciousness. In this article three stereo microphone techniques were briefly explained. When comparing the techniques there are differences. The spaced method can create a more ambient sound and a wider stereo image. With the X-Y method a narrower image is produced.

It is quite clear that a number of procedures must be carried out before recording takes place. Adjusting room acoustics, getting the right type of guitar for the music and giving the guitar a good service can eliminate problems that might occur further on down the line in the recording chain.

Whatever recording method is used, it is good practice to experiment with microphone positioning (microphone height can vary the tone while diastance effects the ambience). If possible, try out different microphones. You will be surprised at the tonal differences between various condenser mics.

As with all recording it is beneficial to experiment. The techniques explained in tis article are only to be usede as a guide. Try out different microphones and try mixing them. Currently condenser microphones are available in several different polar patterns, so try using different pick up patterns.

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