Q. Can you advise on recording acoustic guitar in stereo?

Published in SOS September 2009
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Various

Just wondering if you could give me some advice on recording acoustic guitars. I'm finding it very difficult to get a clean and strong stereo sound. I am recording on to a Korg D32XD and I am using Rode M3 and Shure Beta 58 mics. Could you give me some help with mic positioning, and should I also run a direct line in? if I duplicate the tracks and pan one left and the other right and use phase, will this help with achieving a full stereo sound without making the signal too mushy?

Lennie Wiggins

As a relatively compact sound source, an acoustic guitar doesn't generate much stereo information, so miking with a single mic and then using pseudo‑stereo processing in the mix may be more effective than miking in stereo.As a relatively compact sound source, an acoustic guitar doesn't generate much stereo information, so miking with a single mic and then using pseudo‑stereo processing in the mix may be more effective than miking in stereo.

SOS Features Editor Sam Inglis replies: Before you start, it might be worth asking yourself why you particularly want a 'stereo' sound. Plenty of classic records have been made with a single microphone on an acoustic guitar, and just because you have two microphones and two speakers doesn't necessarily mean there will be any benefit to recording in stereo. With two microphones that are so different, many of the classic stereo miking techniques won't work particularly well, as they require two identical mics. The Beta 58 isn't a mic that would typically be used for miking acoustic guitar in any case, so unless you have some particular reason for wanting to record in stereo, I personally would focus on getting a good sound with the M3 alone.

The conventional place to start with acoustic guitars is to point the mic at the place where the neck meets the body, at a distance of perhaps 12 to 24 inches. Move further away and you will get a somewhat bass‑light sound with more room reflections and ambience; move closer and you'll get a less balanced but perhaps pleasing tone.

If you are dead set on using both mics, my initial suggestion would be to use the Beta 58 as a close mic — perhaps a foot or less in front of the neck/body join — and experiment with alternative positions for the M3. It's possible to get good results by pointing it over your shoulder, at the bridge, at the end of the neck looking towards the body of the guitar, or just somewhere in the room to pick up an ambient sound. In most cases, the acoustics of the room will make a huge difference to the resulting sound, and it may be worth experimenting by moving to different rooms in your house, or hanging up duvets or similar to deaden the acoustic.

If you duplicate a single track and pan one copy hard left and the other hard right, all you have done is effectively double the volume — it will still be mono. It is possible to create 'thickening' effects by delaying or otherwise processing one of the copies, but you would be better off getting the sound right at source. It's definitely not a good idea to simply flip the phase (polarity) on one side, as the two tracks will cancel when the song is played in mono.

If the guitar has a pickup, by all means record a DI signal to blend with the mic at mixdown, if you like the results.

SOS Editor In Chief Paul White adds: An acoustic guitar is a relatively compact sound source and so doesn't generate much stereo information — the sense of three‑dimensional space is down to the room acoustics rather than the instrument itself. To make the reverb sound seem larger than life, try delaying just one of the stereo reverb or ambience outputs by 50 to 100ms more than the other. Depending on the DAW you use, you may have to set up two identical reverbs on two sends to achieve this. Alternatively, use two very different mono reverbs, and pan these left and right. A short, bright ambience on one side and a longer decaying reverb on the other can work well if there's space in the music to allow for more than a hint of reverb.

However, you can force the instrument itself to be 'stereo' by resorting to trickery. One approach is to use two microphones aimed at radically different parts of the instrument and then pan these left and right. A popular choice is to mic the body in the usual way (mic aimed at the neck/body joint or the bridge) but then add a second mic halfway up the neck. The two sounds will be very different but work well in stereo as long as the player doesn't move too much during performance. A variation on this is to use the DI output, where a pickup is fitted, but also mic the instrument and, again, pan these signals left and right. In all cases it is advisable to check that the sound works in mono, as phase differences can cause some pretty radical tonal changes. For this reason, like Sam I wouldn't recommend using phase alone to create stereo effects, but there are phase‑related processes that are mono compatible. 

The usual technique to maintain mono compatibility is to pan the original mono signal to the centre, process a copy of the sound in some way and pan this left, then take a further polarity‑inverted version of the processed signal and pan it right. If you play the recording in mono, the two processed tracks will cancel, leaving you with your original sound intact. The kind of processing you can try for the 'side' channels includes short delays, mild chorus or EQ. Adding a lot of bumps and dips to the EQ curve (for example, using a graphic EQ and pulling alternate faders up and down) can generate a neat pseudo‑stereo effect. For this to work correctly, it is vital to ensure that the two added effect channels carry exactly the same signal at the same level, and that just one of them is polarity‑inverted (using a phase switch or plug‑in). Some DAWs provide you with stereo 'faking' plug‑ins that do the EQ and phase manipulation for you, so if you have anything like that available, it's worth giving it a try.  .


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