In the previous section of this series (Selecting a Mic) we mainly described mono miking, and in a lot of cases that’s as far as you need go, even when the guitar is a major part of the mix. However, there are a number of multi-mic techniques that can be of use. Because much of the art of recording acoustic guitar is concerned with blending the tonalities of the guitar’s body, strings, sound hole and neck into one cohesive sound, one approach is to use different mics to capture individual elements of the sound. These individual elements can be mixed to create the overall tonal balanced you’re after — almost like a sort of natural EQ. A mic at the sound hole could provide warmth, where one on the neck could provide extra brightness, for example.
The main challenge when using such a technique is to make sure that all the different signals are in time with each other when mixed — if there are delays between signals, this could cause phasing problems. Some engineers get around this problem by placing all the different mics at exactly the same distance from the guitar’s sound hole, and this can be successful. However, others record each of the mics on a separate track and then attempt to match their phases when mixing down. (If you’re not already familiar with this, an upcoming TTOTD will describe the techniques in detail)
Many acoustic guitars now incorporate a piezo transducer under the bridge saddle and can therefore also produce a DI feed. While it might be tempting to simplify the recording task by recording only this DI signal, the result is usually disappointing when compared to the same instrument miked up properly. An under-saddle transducer, however, effectively only picks up vibrations from the strings, albeit that their vibration is influenced by the rest of the instrument, whereas a microphone, suitably placed, will pick up vibrations from every part of the instrument, combined with audio reflections from the immediate environment, making for a much more natural sound. Having said that, pop records don’t always demand accuracy and sometimes you can get a sound that works well within a mix by combining the harsher DI’ed sound with miked sounds.
Multi-miking is also used for recording guitars in stereo, or for creating pseudo-stereo effects. For solo guitar recitals and small ensemble work, stereo miking can be an interesting alternative, though it can make the location of the guitar in the stereo image less solid, and more difficult to pan precisely when mixing. It is possible to use any of the range of stereo mic recording techniques (See WFTD Blumlein). However, a number of engineers favor pseudo-stereo effects, such as panning mics pointed at the body and neck of the guitar to opposite channels. Alternatively, you could use one mic over the guitarist’s shoulder and another 6″-12″ from the middle of the guitar neck. The advantage of this approach is that the neck mic produces a bright, detailed sound with very little bass end, and will cause less low-frequency phase cancellation if the track is ever played in mono. Having different tonalities at either side of the stereo image can provide a wider, more interesting stereo image, though you’ll probably want to avoid extreme panning unless you’re after the illusion of a guitar 10 feet wide!
As with any studio recording, the composition of the cue mix you feed to the guitarist will be extremely important, so be prepared to take a little time over it. (An upcoming TTOTD goes into this in detail if you need a few pointers.) One thing to particularly bear in mind is that, given the sensitivity of the mics traditionally used in acoustic guitar recording, it’s easy to pick up obtrusive spill from the cans. Solo the recorded track to check for this, and if there’s a lot of spill coming through (from a click track, in particular) then consider turning down the overall cue mix level or using a different pair of headphones – closed-back models are obviously best in this application.
One Last Note
The way some guitarists move as they play can be vital to the sound they produce. However, any movement of the guitar in a studio environment can play havoc with carefully tweaked mic placements. If you find that you are often encountering this problem, then you might consider investing in a miniature microphone, which can be fixed to the guitar itself. A number of companies manufacture miniature mics for this use, one of the best being the Fishman Ellipse Blend system, though a cheap lavalier mic might do the trick if you’re on a budget.
For the final part of this series, we will discuss acoustic guitar processing and techniques for helping the acoustic guitar sit better in the mix. See you then.