Recording Acoustic Guitar: Advanced Techniques M/S Pair

Andrew —  — 3 Comments

acoustic ms pair

As we know from our previous look at recording acoustic guitar, using a microphone gives you much more control over the guitar tone and a more natural sound than you would get through a built-in pickup. If you want something a little more advanced and a bit special for your guitar sound, then record it in stereo.

You might think a stereo technique for acoustic guitars is overkill since it’s such a small  instrument compared to something like a grand piano which you would expect to record in stereo. So why isn’t a single mic enough?

Honestly, the best way to find out is to give it a go and hear the difference yourself. The ‘middle and side’ technique or ‘m/s’ is the perfect tool for the job, because it allows you to listen to the mono mic and then fade up the stereo. It will also give you a very natural sounding stereo image with minimal phase issues if you decide to make it quite narrow in the mix. It is slightly more fiddly to set up then just rigging two mics and panning them left and right, but it is a more versatile technique and can give really nice results.

How To Rig An M/S Pair

You will need:

  • A cardioid or omni mic depending on your room – I’m using a C451. This will be your ‘middle’ mic
  • A figure 8 mic, if you’ve got a ribbon mic then that’s ideal but a switchable pattern condenser will work well too, as you can see above – I’m using an sE: X1R ribbon. This will be your ‘side’ mic.

Start with the middle mic, which will give you most of the sound of the guitar so rig it to give you a nice full tone. About 8-9 inches from the guitar, aimed just above the sound hole is probably a good starting position for this technique.

The fig. 8 mic needs to be as at 90° to the middle mic, so that it is parallel to the guitar. The closer you can get it to the other mic without actually touching, the better. In this position, the ‘dead’ axis of the mic is pointed straight at the body of the guitar, so it’s not going to pick up any sound directly from it. The front and back of the mic look along the length of the guitar, so you can imagine how it picks up the ‘Side’ (which is the stereo component) of the guitar sound.

Setting Up The Mixer

You will need:

  • one channel for the middle mic
  • two identical channels for the side mic

The easiest way to duplicate the side mic is often simply just to record the same input onto two different channels. You can do it with aux sends but be careful if your DAW doesn’t have delay compensation built in because it may cause phase issues at the next stage.

Pan the two side channels hard left and right, and phase invert the second.
If you can’t find a phase invert button – open an eq plugin and look for a Ø symbol

Use the middle mic to set the level, and then fade up the side channels. The level and tone of the guitar won’t change that much if at all, but you will hear the stereo image spread out from the middle as you fade up the side. The really great thing about this technique is that you can use it very subtly with just a touch of the side mic, or have it faded right up to get an enveloping but very natural sounding stereo image.

Listen And Adjust

Once you have got the mics rigged and the mixer set up, listen closely to how it sounds before you hit record. The chances are that one side of the image will sound stronger than the other, so move the mic pair in the opposite direction to compensate.

If you have trouble getting the left/right balance right without compromising the tone, then try moving a couple of inches further away. Alternatively you can rig the fig. 8 mic horizontally so that it looks straight up and down across the front of the guitar, rather than left to right. This will mean that you get more separation of the high and low strings across the stereo image, which is why I prefer having it vertical, but it is much easier to rig and balance.

When To Use M/S Stereo

The versatility of m/s recording means that you can use it in a variety of applications. A tiny bit of side will give the guitar a full sound but won’t overcrowd an already complex mix. In something like an acoustic track or a solo piece where the guitar is more dominant, you can use a lot of side to get the full stereo sound. If you’re not sure whether you will use it or not in a mix, then you have nothing to lose by rigging the side mic because you can always leave it out and stick with mono.

When Not To Use M/S Stereo

If you are recording an acoustic guitar with another instrument at the same time, m/s might not be suitable because the side mic can easily pick up spill from the other instrument and cause problems in the mix later.

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