You might be totally in sync with your home-recording rig, but tracking acoustic guitar presents some unique challenges and there are guidelines to follow.
Mic it. Sometimes an acoustic guitar with a pickup that's recorded through a DI can be just the ticket for a certain kind of track. But for a more natural sound, using a microphone is the way to go the vast majority of the time. Choosing a mic with a cardioid polar pattern will help reject unwanted ambience, and using a quality small- or large-diaphragm condenser microphone is a tried-and-true method for capturing the complex tone of an acoustic guitar.
Small-diaphragm condenser mics, generally speaking, have a more uncolored sound and respond to transients faster. They tend to give an accurate sonic representation of what the guitar sounds like in the room. Large-diaphragm mics can sound great, too, and tend to lend more of a thick color of their own to the timbre—especially in the case of tube mics.
Mono is your friend. Stereo miking techniques, such as x/y or m/s (mid/side), can be terrific when a guitar needs to be the focal point of a track. But I shy away from recording in stereo most of the time, for a few reasons. First, it's more difficult to record in stereo—especially if you are serving as your own engineer and the guitarist. It's next to impossible to hear things like phase relationships between two mics when you are also hearing the sound source directly. Second, if you are recording guitar parts for a song that has other instruments such as bass, drums, and electric guitars, a stereo acoustic-guitar image probably won't be desirable anyway. You'll want to pan a mono guitar part in the mix so it becomes a part of the overall sonic picture and lives in its own space, and leaves space for the other instruments.
Mic placement. My go-to mic placement: about 12" back from the face of the guitar and pointed somewhere in the vicinity of where the neck meets the body. Many folks tend to put the mic right in front of the soundhole, but there's a ton of low-end energy in that vicinity that can really muck up the sound. Experimentation is key, but I've achieved the best results between the soundhole and the neck joint. If you are recording in a room with less than stellar acoustics or a very live character, a reflection filter placed behind the mic can help tame unwanted or excessive early reflections. If you have hard floors and are hearing too much reflection, a throw rug can also be a great thing to keep around.
Compression, filtering, and EQ when tracking. I recommend using a high-pass filter set at about 70 Hz when tracking acoustic guitar. Anything below 70 Hz or so is just unwanted rumble that can build up in a mix and cause problems. Some microphones have a switchable low-cut filter built in, but I usually use the low-cut filter on my mic preamp. Since I'm a UAD Apollo user, I can also insert a plug-in preamp/compressor EQ in my UAD console application. This allows me to easily cut the unwanted lows and compress if I wish. If I do compress when tracking, I do it very sparingly. Once again, this is because when you are serving as the musician and engineer, it can be difficult to hear exactly what is happening with compression while you're also hearing the sound coming directly from the guitar body itself. Best to leave it for the mix!
In the mix. Panning, EQ, and compression are the tools you'll want to use in the mix to make your tracks really “speak." Try employing subtractive EQ first by using a plug-in EQ, boost the low mids up 10 dB or so, and sweep the low-mid frequency band from 150 Hz to 400 Hz. Listen for the frequency that sounds like mud! (I usually find it's somewhere from 190 Hz to 300 Hz.) Now, try cutting that frequency by a few dB, and behold—clarity! Sometimes this is all you need to do, but if you need more cut, try boosting the upper mids around 1.5k to 2.5k. For some added sheen, a high-shelf EQ anywhere from 3k to 8k can add some polish.
You can experiment with compression in the mix to your heart's content. My goal is usually to smooth out the peaks while pushing the guitar forward in the mix. A faster attack will smooth out aggressive strumming and pick attack, while a slower attack will most likely sound more natural. I usually use a relatively fast release and a 3:1 ratio. Set the threshold so you are getting anywhere from 3 to 6 dB of gain reduction, and really listen at quiet and moderate volumes. When it comes to compression and guitar tone, it's a very fine line between cool and overcooked.
I hope you find some of these tips and suggestions helpful. Until next month, I wish you great tone!