Recording Acoustic Guitar — Joff Winks

Over the years I've had many opportunities to record guitars and so consequently have gained a fair amount of experience in this particular corner of the audio engineering world, some of which I'd like to share with you in this blog.

I'm going to focus on a few of my preferred techniques for recording acoustic guitar as I've found this subject can be quite challenging at times and I've received numerous requests for assistance from friends regarding the recording of their instruments.

The first thing to mention about the acoustic guitar is that despite sharing approximately the same fundamental tonal range as its electric counterpart, E2 to C6/D6 on 20/22 fret instruments respectively; the overall frequency range produced by the acoustic instrument is much wider, electric guitars being limited by their pickup, amplifier and speaker design.

Typically the electric guitar exhibits few frequencies above 5khz, whereas the acoustic instrument produces frequencies that can happily exceed 10khz, exhibiting a complex array of harmonics and overtones that contribute much to the instruments timbral character. It is therefor vital to choose the correct microphone for the job.

Condensers are usually the mics of choice when recording acoustic guitar as they capture a wide range of frequencies, are moderately flat across the frequency spectrum from 20hz to 20khz and are much more sensitive than dynamic designs. So abandon your trusty SM57 for this task.

I've found through experimentation that small diaphragm designs work better than the larger capsule offerings as they behave a little better off axis and are easier to place discreetly in front of the guitar. Recently I've been using a pair of Rode NT5s, which are a pencil design and have a cardioid polar pattern. However, I've had fabulous results with the famous Neumann KM184 and AKG C451s. As you can see form the photograph below I've got the mics in their elastic suspension mountings. This radically reduces any mechanically transmitted frequencies travelling through the mic stand, ensuring that the recording is as clean as possible. If your mics didn't come with mounts you can always purchase a universal type that should work just as well.

If you're unsure about the term cardiod or the various properties of different microphone polar patterns you might want to buff up your knowledge by clicking here

So now you've got the mics where do you put them?

Most of the problems recording an acoustic guitar begin with trying to mic the sound hole. I've heard many examples of this method but have never obtained a balanced recording using this technique. The frequencies emanating directly from the sound hole don't accurately represent the complex array of frequencies that constitute the overall timbre. You may have noticed from your own guitar that many of the high frequencies seem to come from the neck and face of the instrument. Indeed if you listen carefully you'll find all sorts of resonant areas other than the sound hole. So lets rethink miking the instrument at the sound hole.

Mono Recording

Now, what I'm about to suggest might sound a bit weird but if you haven't tried this before take a leap of faith and trust me. You won't regret it!

You'll want to position the mic at a working distance of between 6″ to 10″ from the top shoulder of the guitar just above where the neck joins the body. This is usually fret 14 on modern steel string instruments. The further back the mic is from the guitar the more room” sound you'll be capturing, conversely the closer the mic is to the source the less room sound will be captured. It's really important to keep in mind, when working with any directional mic, the bass proximity effect” that occurs in close mic situations. That is, the closer the mic gets to the source the more exaggerated the bass frequencies become. So try to resist the temptation to mic the instrument too closely if you want to maintain a natural, balanced recording.

I would suggest starting with the mic on axis to the guitar and making a series of recordings as you progressively move the mic off axis. It's possible to obtain more bass frequencies by angling the mic towards the sound hole and brighter frequencies by angling the mic along the neck of the guitar. Proceed methodically and take notes of where the mic is for each test recording that you make. This way you can review your recordings to find the mic position that really works for your instrument and room.

Stereo Recording

If you want to progress to a stereo technique it's actually quite a simple process and can work wonders in post production!

I've always favoured the XY coincidental (intensity dependent) stereo technique for acoustic guitars over a spaced pair configuration as the phase coherence is much better. Although

I've also had great success with the less commonly used MS set up. I do want to write a blog concentrating on MS as I think it has much to offer but is beyond the scope of this blog.

Before I continue if you are unfamiliar with stereo mic techniques or the term phase you'll want to click here

For this stereo technique you'll need two mic stands an XY mic clip or a stereo mounting bar and a matched pair of mics. Our central concern is to position the mic capsules between 90 and 130 degrees to one another so that they are overlapping forming a cross. The central point between the two mics should face the guitar at roughly the same working distance as before and aiming towards the top shoulder of the instrument. The mics need to be panned hard left and right for the stereo image to become apparent.

It's still important to observe the same working methodology as for the mono mic technique to obtain a natural balanced stereo recording.

The XY stereo technique offers some great advantages over the mono version. In post production it allows the guitar to sit at the edges of the mix, clearing the centre of the stereo image for vocals or lead instruments. It's also very mono compatible and as such translates well to small speaker systems with limited separation between speakers or mono systems… yes they still exist!

Below is a photo illustrating a similar XY configuration but this time using a stereo mounting bar. I find that this is very useful as it eliminates the need for two mic stands.

In conclusion here's an example of a nylon strung, classical guitar recorded with the above stereo technique. I've applied some compression to bring out the inner detail and processed

the recording with EastWest's Spaces reverb plugin.