How to: Recording an Acoustic Guitar

Hi everyone, my name is Markus Orthaber from Austria, Europe. This blog post is my contribution to week 1 of the course Introduction to Music Production at Coursera. I will do a short how to on recording an acoustic guitar. Actually a steel-string western guitar.

I find that the first critical thing in recording an acoustic instrument is to find the sweet spot in your recording room. Try several different positions and listen for sonic differences in order to find that sweet spot. In my studio I use moveable broadband absorber panels and absorber “clouds”, i.e., broadband absorbers hanging from the ceiling, in order to avoid recording between naked walls. This dramatically reduces artefacts like comb filtering. My approach is to always try to make the instrument itself sound as best as possible before even thinking of capturing it with a microphone. As you might have guessed the acoustics of the recording room itself plays an important role in that equation as well.
For this specific example the guitar stool had been positioned rather centrally in my 24m² recording room below a cloud-absorber and above a rather thick carpet. Furthermore the otherwise naked walls on two sides of the recording position have been covered by one moveable broadband absorber each. As it happens a stationary 1D diffuser with an area of approx. 4m² is positioned behind the guitarist about 4m away.

Secondly, one has to think about how the instrument should sound in the final recording. What role is it going to play? In our example at hand, the acoustic guitar plays one of the main roles in the finished song since it is a quiet ballad. Thus, I opted for capturing it rather space-filling. Four microphones have been used to achieve a good stereo image as well as a bit of depth and some of the fingering sounds from the fretboard.
The stereo image has been captured by a matched pair of small diaphragm condensers, specifically Rode NT-5 upgraded with Michael Joly MJE-384K capsules. I find those capsules less harsh in the treble region. The pair has been used in an XY-arrangement on a stereo rail. One is pointing towards the 12th fret and the other one at a point just behind the bridge, both with a distance of about 25 – 30cm to their respective region.
The third microphone is a large diaphragm condenser, an Audio Technica AT4040, pointing towards the body-neck junction of the guitar to capture a balanced recording of the instrument. This one has been positioned farther away at about 40 cm to the guitar to obtain some natural depth.
The fourth and final microphone is another small diaphragm condenser, an Audio Technica AT2031. It has been positioned behind the shoulder of the guitarist about 60cm above the neck and flush with the front side of the neck. In my opinion this nicely captures some fingering noise, adds some more depth to the recording and also gives an alternate sound that may be handy to use at mixdown. On that microphone the built-in roll-off switch has been activated in order to avoid capturing too much low-end which is already captured by the other 3 mics. This roll-off switch activates an high-pass filter at 150Hz with a steepness of 6db/octave. Furthermore a wind screen has been used on that mic in order to attenuate some of the high-end and avoid unnecessary harshness. The following pictures give you an impression of the microphone positions relative to the guitar.

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DSCN1397

All four microphones feature a cardioid as their polar pattern. As an alternative you may try a large diaphragm mic with an omnidirectional polar pattern instead of the AT4040 to capture an even more natural image of the guitar and some more of the recording rooms response. I don’t have an omnidirectional microphone at hand and thus didn’t try that approach so far.

As usual all of these microphones are connected to the microphone inputs of the audio interface with symmetric XLR microphone cables. The interface that I am using is a Focusrite Liquid Saffire 56 which connects to my DAW via firewire. In order for the microphones to be able to operate, so-called phantom power (48V) is necessary. Moreover the high pass filter switch on the interface is engaged to avoid any low-end rumble. The gain on the interface is set such that the input meters show a value of about -6dB at maximum in order to leave enough headroom before clipping. Especially make sure that the gain of the stereo pair inputs is adjusted similarly in order to get a proper stereo image. Then everything is set to record your acoustic guitar.
The following playlist contains short snippets of some preliminary acoustic guitar tracks of a song that I wrote some time ago and started to record recently with my band. This recording has been made by utilizing the method outlined above and no processing has been used on the tracks apart from positioning the mics across the stereo panorama.

The techniques presented here are based on the books [1], [2], [3] and a good amount of trial and error.

I hope I could give you some insight on my approaches to recording an acoustic guitar and want to thank you very much for reading this post. I am very much looking forward to your comments.

All the best and keep the music flowing,
Markus

References:
[1] Bobby Owsinski, The Recording Engineers Handbook, 2nd Edition, Alfred Music Publishing (2009)
[2] Mike Senior, Recording Secrets for the small studio, Focal Press (2014)
[3] Andreas Mistele, getting pro, epubli (2012)

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