1. One Microphone MonoA great way to record an acoustic guitar is using one microphone. Though using one microphone creates a mono signal, this can be of great benefit when trying to fit the guitar in a larger mix. A good place to start is with the microphone aimed at the 12th fret of the guitar about 4-6 inches away. The tone of the microphone can be adjusted by changing the angle and distance between the guitar and the microphone.
2. Stereo Spaced PairYou can also record an acoustic guitar using the spaced pair technique. This involves using two microphones and panning one hard left and the other hard right. When done properly, this creates a very natural guitar recording and may be the nicest sounding method of the three. Though this method sounds very good, it may not fit well when mixed with other instruments, especially if there are already a lot of stereo recordings. The spaced pair technique works best on tracks where the acoustic guitar is the main rhythm instrument.
To record a guitar in spaced pair, one microphone should be placed a few inches away from the 12th fret and the other a few inches from the bridge (not pointed directly at the soundhole). Once again, the tone is adjusted by changing the angle and distance of the microphone. Finally, the 3-to-1 rule is used to avoid phase cancellations between the two microphones. This means that the distance between the two microphones must be at least 3 times the distance between the microphone and the guitar.
3. Stereo XY TechniqueThe third technique for recording an acoustic guitar is XY. With this technique, the microphone capsules are placed as close together as possible and angle at between 90° and 120°. A good place to start is with the microphones 6-7 inches away from the 12th fret of the guitar. Though the XY technique does not create as wide of a stereo image as spaced pair, it has the advantage of being much easier to set up. Since the microphones are placed so close together, there won't be any problems with phase cancellations. Ideally, the XY technique should be done with a matched pair of small diaphragm condenser microphones.
If you're looking to record acoustic guitar, we recommend the Audio-Technica AT2021. This microphone will produce a clear tone with plenty of high end, and works great for mono and stereo acoustic guitar, as well as drum overheads.