Mixing Acoustic Guitars

Acoustic guitars are one of the most dynamic and expressive instruments used in modern music. They have a broad frequency range covering almost the entire audible spectrum. The instrument can serve many different roles in an arrangement as a harmonic, melodic, or percussive element. All of these factors will affect how you approach both the recording and mixing acoustic guitars.

Context
The first thing to do is think about its role in the song/mix. Is the guitar the main harmonic instrument? Is it supposed to enhance or thicken other harmonic instruments like electric guitars? Is it enhancing the melody, playing arpeggios or single notes? Is it a percussive element more like a shaker just to fill out the rhythm section? Figure out the goal, then you can begin processing.

Tone control
Depending on the guitar, microphone, pick, player and role in the arrangement, acoustic guitars always require at least a little equalization to fit in a mix. Cutting of nonmusical sub frequencies (everything below 100Hz) is a must. A low shelf may be required to tame the remaining low-end. In the midrange, take out any unflattering frequencies causing 'boxiness' or anything that might mask the vocals. A broad, gentle high shelf boost can enhance articulation and an overall more sparkly sound. The general strategy is to remove what you don't need, then enhance what you do.

Dynamics
An acoustic guitar performance is often extremely dynamic, which is often a problem. A compressor will even out the differences between loud and soft notes and help keep the level more constant throughout the track. It's easy to take it too far, so keep the gain reduction to no more than 3-4dB. The compressor's attack control will allow you to clamp down on the beginning of the notes, or when set slower (about 20-50ms) will enhance the transient which helps it stand out more in the mix.

At this point you may want to adjust the sound envelope further though use of a transient shaper. This tool can increase or decrease pick attack, and separately adjust sustain.

Depth
Sending your acoustic track(s) into a stereo reverb will add space and distance to the sound. The trick here is to not wash out the sound in a ton of reverb, but just to move the move the mics back a bit into an imaginary room. Usually, a short room type verb with the highs rolled off is the best bet. Try to make the reverb sound like an office or large bedroom - short decay with and a bit of early reflections. The predelay control will separate your source from the room.

Summary
And so, following the above strategy you should now have an acoustic guitar track with a balanced frequency response, even dynamics and sense of space around the instrument, (if that was what the track required). The track is ready to be put in the mix with the other instruments. Tweak the EQ in context with the other tracks, adjust the reverb send amount, and even EQ the reverb if needed.

Examples
Acoustic Raw
Acoustic Processed

DOs and DON'Ts of Acoustic Guitar Recording

DO keep your strings fresh (and keep the ends cut short)
DO wash your hands before and after playing
DO listen to the instrument to find the best mic placement
DO wear closed-back headphones to avoid escaping noise
DO find the spot in the room where the guitar sounds best
DO try to breath quietly through your nose (yes this is a problem sometimes!)
DO try to stay in the same position in front of the mics
DO try different thicknesses of picks for different sounds

DON'T forget to tune often
DON'T place your mics close to the sound hole
DON'T stop if you make a mistake
DON'T assume the built-in pickup actually sounds anything like your guitar, not to say it can't be useful at times
DON'T forget to empty your pockets of keys, change and cellphone
DON'T rush through the recording, take your time now to get it right.

5 Tips for a Great Acoustic Guitar Recording

Here are 5 tips for getting great acoustic guitar recordings in your home studio.

1 - Guitar Selection: Every brand and style of guitar has a different sound. Yamaha or Martin, a full size Dreadnaught or a smaller Parlor style. They all sound different, your favorite or most expensive guitar may not be the best for every situation. Having a few choices available will help you get a lot closer to the sound that's right for any song.

2 - Tuning and New strings: It's very simple but often overlooked. Before an important recording session, put new strings on your guitar. Before every take make sure it's perfectly tuned. If you use a capo remember to compensate with your tuning.

3 - Listening: Instead of just putting the mic where you think it will sound good, actually get up and walk around and listen to the tonal changes in each part of the guitar. When you find a favorite spot, put your mic there. This is a great starting point for a mono (single mic) recording as well as a good warm-up for your ears. If the song calls for a stereo acoustic guitar part, you still need to find the sweet spot for the mics. How high or low, close or far, you don't know until you take the time to listen.

4 - Mic Choices and Position: In the studio it is unlikely you will prefer the sound of a dynamic mic on acoustic guitar compared to a condenser, but if you've never heard it, by all means try it, try all your mics. Large diaphragm condensers and small diaphragm condensers are the most common choices for acoustic guitar recording. Again, listen to the differences between mics and where you place them. The closer the mic is to the instrument the more 'Proximity Effect' (an exaggerated low frequency boost in the mic) there will be. Avoid using mics that might exaggerate lows, mids or highs in an already too dark, middy or bright guitar. Pick a mic that complements or balances the sound, dark mic on a too bright guitar for example.

5 - Processing: After you've done your best capturing the guitar right, you still may need to do some work to get it playing nice with all the instruments. In the mix you'll usually need a bit of processing to make room for other instruments, control dynamics, among other things. Generally you need to: cut the very low frequencies, shape the mids to make room for vocals, compress a few dB to even out the performance and add a little reverb to give it space.