Acoustic Guitars
An acoustic guitar contains many harmonics in the sound output and in order for all these to be picked up accordingly, a suitable microphone is to be used. A condenser microphone is first choice because it can pick up the high frequency detail accurately. Whether recording live or in the studio, one of the most common mistakes in recording the acoustic guitar is the positioning of the microphone. The acoustic guitar produces sound from the entire body and not just the opening hole. This is what gives the overall sound its timbre and not just the lowered mid sound which is what mainly comes from the sound hole. It is very important to position the mic in such a way that it covers the range of the whole guitar so that a full representation of the original sound can be achieved. Signal strength will undoubtedly be reduced in this situation but the tone will be much fuller. Dynamic mics are not usually sufficient for this application as they have a very limited frequency range.
The key to making a guitar sound good in the studio is getting the environment it is played in to sound as bright as possible. The acoustic guitar is naturally a bright instrument so they way that we would expect this to be heard on a recording is also bright. If the room has poor acoustics, the overall sound can be made very dull by it. So when recording guitar, there are two choices. Either make the room as bright as possible or as neutral as possible. Preferably, most engineers would rather have a more natural sound than adding artificial reverb later but in some cases this cannot be helped. Adding reflective material around the guitarist and even under him can lift the sound to make it sound more live.
The guitar can be recorded with either a mono or stereo microphone technique.
If using a mono microphone, it is best to point the microphone at about the 12th fret, about 2 foot back. This will give a good blend of the whole sound of the guitar. If the sound is too 'boomy' then moving the microphone back further will achieve a good result. Conversely , if the sound lacks body, then the mic should be brought forward. Unlike other instruments, there are many 'sweet spots' on the acoustic guitar. These can be found by moving your head around the guitar as it is played or by using a good pair of headphones and moving the microphone.
There are two main advantages to using a stereo set up for recording an acoustic guitar. More of a stereo image can be created as the recordings can be panned. Also, the microphones can be pointed at the main body of the guitar and the neck to produce a more balanced, fuller sound. Any combination of microphones can be used in this application.
One way of setting up the two microphones is by having one pointing down the body of the guitar while the other is pointed at the head stock or the body. Experimentation is key to achieve the desired results. If the guitar is electro-acoustic and if inputs allow, recording the pickup and blending it in with the others can often work as it adds a very different tone. It is a more metallic tone usually but this depends on the quality of the pickup in the guitar.
The diagrams below show the positioning of the microphones mentioned previously.
