Tech Tip:Recording Your Acoustic Guitar, Part 2
Part 1 | Part 2
by Dennis Kambury
A tale of two mics
Using a single mic and a single guitar, you can uncover a broad range of tonalities. From bright and crisp to warm and woody, where you place the microphone makes all the difference. Adding a second mic for stereo will really expand your possibilities. We'll look at some common techniques - and some things to watch out for - to make the most of your stereo recording adventure.
From A to B
The most obvious technique for stereo is to take your two mics - mic A and mic B - point them at different parts of the guitar, and punch the record button. For example, direct mic A towards the 12th fret, from around 6" away from the guitar. For mic B, aim at a point below the bridge, again from about 6" away. This will give you a nice stereo perspective. To lessen phase cancellation and improve the image when listening in mono, keep mic B at least 18" away from mic A. (The "3-1 rule" dictates that the second mic should be at least 3 times the distance from the first mic as the first mic is from the source.)
The XY technique
No, this isn't a method to guarantee your offspring will be male! As with A-B miking, the XY technique achieves stereo nirvana using two identical (or at least similar) mics. Instead of wide separation, however, the two mics are set up so that the capsules are practically touching. The rear of the mics angle outward from 90° - 120°. They'll look something like this - / \ - with the capsules at the top end. While this won't give you a stereo spread as spacious as A-B miking, it still opens up the guitar nicely, and is very mono-compatible.
Mid-Side miking - my personal favorite - is a little less intuitive, a little more involved, and produces a great stereo sound that's completely mono-compatible. The general idea (without getting into the math of it) is to capture left, right, and center information from 2 sources. The first source, the Mid microphone, is generally a cardioid-pattern condenser positioned much like you would position a single mono mic - i.e., 6 or more inches from the guitar. The second source, the Side mic, must be a figure-8 pattern, and instead of being pointed at the guitar, it is oriented perpendicular to the direction of the Mid mic.
To decode the MS information, split the Side mic signal to the mixer with a Y-cable, and put one cable into Channel 1, the Mid mic signal into Channel 2, and the second Side signal into Channel 3. Pan Channels 1 and 3 left and right, respectively, and invert the polarity on Channel 3. Leave Channel 2 (the Mid signal) panned to center. When you bring up all three channels, they combine to create a very natural stereo image.
The techniques I've outlined are just sketches. Experiment with mic placement, distance, and different types of microphones, and find what works best in your situation. To delve into the world of miking techniques, I'd recommend the Hal Leonard publication, "Professional Microphone Techniques." Along with mic techniques for instruments and voice, it includes a CD-ROM that lets you actually hear the differences. Roll tape!