Recording guitar is rarely ever as easy as sloppily plopping down whatever mic’s handy at the moment in front of the speaker grille and hitting record. Majority would even argue that mic choice and placement only play bit parts in a larger production that involves pre-amps, guitar amps, cable length, A/D D/A converters, tracking through a console clean vis-a-vis applying processing going in, and of course, the choice of guitar itself! Instead of writing a fully comprehensive work (and a very, very long discussion and debate), this article aims to address some basic guitar micing technique using a dynamic cardioid microphone (such as the venerable SM57) and a condenser (such as a Neumann u87).
1 mic technique
If the situation calls for using one microphone, you can position your dynamic mic either as close to the speaker grille cloth as possible (less ambiance) or 3-6 inches away, either pointing to the center of the cone or off-axis. Listen through your monitors how the speaker sounds like, and change cones if you aren’t satisfied (as in the case of a marshall 4×12). Once you’ve decided on which cone to record, fine tune the guitar sound by angling the mic towards or away from the center of the cone as it makes a difference in the tone coming into your recording. A condenser is generally placed a bit farther because of its higher sensitivity (and in some cases, lower clipping point with regard to SPL handling).
2 mic technique
Applying the technique above, one may also add another microphone such as a condenser (or a ribbon mic, if you prefer) to get a different flavor coming from the same guitar and guitar amp. When placing the second mic, be sure to keep in mind the 3:1 phase rule, wherein the second mic should be at least 3 times as far from the source as the first mic so as to minimize phase. One doesn’t necessarily have to follow this rule, and in some situations where an out of phase guitar is called for by creative considerations, just go for whatever fits the music and gets you the sound that you’re looking for.
3 mic technique
One can use the 2 mic technique above in conjunction with one more microphone placed at a distance from the sound source, serving as the captor of the sound of the guitar amp is it is being influenced by the recording environment. An omni-directional condenser mic is usually used for this situation because of its 360-degree pickup pattern.
One constant principle to remember is that in recording guitar, the overall tone is largely influenced by the guitarist’s technique above all. An unskilled guitarist playing a rare vintage Les Paul through a great sounding Mesa Boogie will still sound unpleasantly unsatisfying.