The acoustic guitar has a delicate timbre which you can capture through careful mic selection and placement. First prepare the acoustic guitar for recording. To reduce finger squeaks, try commercial string lubricant, a household cleaner/waxer, talcum powder on fingers, or smooth-wound strings. Ask the guitarist to play louder; this increases the “music-to-squeak” ratio!
Replace old strings with new ones a few days before the session. Experiment with different kinds of guitars, picks, and finger picking to get a sound that’s right for the song.
For acoustic guitar, a popular mic is a small-diaphragm condenser with a smooth, extended frequency response from 80Hz up. This kind of mic has a clear, detailed sound. You can hear each string being plucked in a strummed chord. Usually the sound picked up is as crisp as the real thing.
Now let’s look at some mic positions. When you record pop, folk, or rock music, try a spot about 6 to 12 inches from where the fingerboard joins the guitar body (Figure 1-A). That’s a good starting point for capturing the acoustic guitar accurately. Still, you need to experiment and use your ears. Close to the bridge, the sound is woody and mellow. Near the sound hole, the sound is bassy and boomy.
Figure 1. Some mic techniques for acoustic guitar.
In general, close miking gives more isolation, but tends to sound harsh and aggressive. Distant miking lets the instrument “breathe”; you hear a gentler, more open sound.
Another spot to try: Tape a mini omni mic onto the body between the sound hole and bridge, about 1″ from the low E string. (Figure 1-B).
The guitar will sound more real if you record in stereo. Try one mic near the bridge, and another near the 12th fret (Figure 1-C). Pan part-way left and right. Another way to record stereo is with a 90-degree-angled pair of cardioid mics about 6 inches from the 12th or 16th fret, mixed with a 3-foot-spaced pair of omni mics about 3 feet away.
You get the most isolation with a pickup. It attaches to the guitar, usually under the bridge. The sound of a pickup is something like an electric guitar. You can mix a mic with a pickup to add air and string noise to the sound of the pickup. That way, you get good isolation and good tone quality. You might record the acoustic guitar off its pickup while tracking to prevent leakage, then overdub the guitar later with a microphone for its better sound quality.
Some microphones are designed to mount just inside the sound hole against the front surface (Figure 1-D). Their bass is reduced to compensate for the boomy sound in that position, resulting in a natural tone. These mics can provide excellent isolation from the vocal and good gain-before-feedback in a PA application.
Bruce Bartlett designs guitar microphones (www.bartlettaudio.com). He’s also a recording engineer and audio journalist. His latest books are “Practical Recording Techniques 6th edition” and “Recording Music On Location.”