Acoustic guitars are used in all types of music; from rock to a solo classical guitarist. Depending on the type of music, the method for mixing an acoustic guitar can vary.
The notes an acoustic guitar is tuned to range from about 80Hz for an open 6th string to about 660Hz on the 12th fret on the first string. There is a lot more to a guitars sound than just the actual notes its strings are tuned to though. Vibrations from the body and noise from fingering or the pick also add to the overall sound of a guitar.
So what is a good starting point? In many mixes, the first place to start is by rolling off the low end. This can be anywhere from 60Hz for an accoustic set to 100Hz for a rock mix. Next, the boominess can be tackled. The boominess of an acoustic guitar usually lies somewhere between 150Hz for an accoustic mix and 700Hz for a rock mix. Finally, giving a little boost around 2kHz and another in the 15kHz range can add some zing and sparkle to the guitar.
That is about all there is to it. Some people might like to add some very light compression, in the 2:1 range, but I usually just prefer to leave well enough alone.


