The acoustic guitar can produce a rich sound full of harmonics and complexity, making a good recording of this instrument can sometimes be over simplified just because it is an extremely common instrument to play. Recording acoustic guitars is fun and it should be quite straight forward when applying some well used techniques.
Before any recording begins you must make sure your instrument sounds good when you play it. It sounds obvious but it has never ceased to amaze me how often an engineer has to battle against a badly set up instrument in the recording phase. Before recording it is recommended that the guitar is perfectly in tune, no ifs and buts, make sure it is in tune.
Secondly consider fret buzz and squeaks as well. If you have never had a guitar set up by a professional guitar tech and you are about to record, try and do so a few weeks in advance of the recording date. This will cost between $40 and $100 and the guitar tech will level your frets, make sure your intonation is right and also ensure that the playing action of the guitar is low and comfortable. Before recording be aware that changing strings can increase the detail and highs in your tone which can be very desirable. Conversely it can also increase the strings ‘squeakiness’ when sliding up and down the fret board, this may not be as desirable.
So consider if you wish to keep the tone mellow with your old strings or if you want fresh strings to brighten up your tone. The tech can always put the old strings back on if need be. When recording an acoustic guitar I recommend recording it using a stereo microphone technique. To my ear stereo acoustic guitar recordings always sound more interesting and also provide a sense of depth, space and detail which cannot be achieved using a single microphone. You can always ditch a microphone if need be, so stereo recording provides options.
Microphone placement will always need to be tweaked depending on the guitar, the room and the sound that one wishes to achieve. I recommend using 2 condenser microphones for guitar recording. Condenser microphones are more sensitive than dynamic microphones and often have an improved detail in the high frequencies. Condenser microphones require 48 volt phantom power, this is commonly supplied by microphone pre amplifiers but it is worth checking to make sure you have this facility before hiring microphones for example.
You can use any combination of small diaphragm or large diaphragm condenser microphones when you record although it is quite common to use an LDC and a SDC microphone.
Example of LDC and SDC microphones :
Aim the LDC at the guitar body between the bridge and the edge of the body, a distance of around 8-10 inches should be a good starting point. The SDC microphone can be positioned 8-10 inches from the point at which the guitars neck meets the body. You will find the more the SDC microphone points towards the sound hole the more boomy the sound will be come so start with it as mentioned above and adjust for tonal taste. Ask the guitarist to play and have a listen to the sound, fine tune microphone positioning depending what you want to hear. You may prefer a more mellow roomy sound or a more up front and present tone by using a close microphone technique.
When taking recording levels always make sure your DAW is set to record at 24 bit resolution and ask the guitarist to play as loudly as they will and peak the input signal to -12dBFS peak on the input meter. This will allow plenty of headroom and you will make a clear and distortion free recording. By all means experiment with various microphone preamps and microphones to alter the recorded sound.Sometimes a nice warm vintage style microphone preamp can mellow and round the tone out if you have time and options experiment and listen for the tone you want.
In most instances as long as you have set the record level correctly there should be no need to compress the signal during the record phase. However if you like to do this keep the compression light and just apply 3dB reduction maximum to the peaks when being played loudly. Of course you can apply some gentle equalization to the recording but try and get the tone you want by microphone position alone.
Barry Gardner operates SafeandSound Mastering a low cost, high end online mastering studio based in the UK.