Middle Side microphone technique.

Being knowledgeable about stereo microphone techniques is a must if you are a recording engineer. There are quite a few techniques out there that's good to be aware of.

Many of these involve careful calculations of distance between mics and the amount of degrees they should be facing to or from each other. I like coincident pairs rather than the non-incident pairs because there is less worry about phasing issues. Although music is an art, miking techniques is a science. 

Coincident pair techniques like X/Y or M/S work really well close range as well, so when working in bad sounding rooms, there is less worry about the room playing a part in the sound.

The M/S(Middle/Side) technique is a great miking technique for recording acoustic guitar. Although it a little more complicated than X/Y, the pros completely outweigh the trickiness of learning the technique. Instead of ending up with a left and a right signal, you have a direct signal and a controllable stereo sound.

Using two microphones, a cardioid condenser and a figure 8 condenser, position them 30-50 cm from the twelfth fret. You should have the cardioid pointing to the twelfth fret which is often thought of as the sweet spot of the guitar. Then position the bi-directional mic as close to the cardioid as you can, either under or over the instrument.

Turn the figure-8 so that it is facing parallel to the instrument, effectively picking up the sound waves that are radiating from both sides of the guitar. Now the tricky part is that you have to route the bidirectional mic to a third channel via an aux(post-fader!) and invert the phase of the third channel.

So in effect,

• One channel has the cardioid, or the direct sound of the guitar.
• Second channel has the bi-directional, picking up the sides.
• Third channel has a copy of the bi-directional, but out of phase with the second channel.

With your desk, or recorder in mono, align both figure-8 channels so they completely cancel each other out. Two sound waves completely out of phase cancel each other out so you just move the faders together until you hear no sound.

Now if you revert back to stereo they appear again, but you should pan them hard left and hard right. If everything goes according to plan you should now have a full-bodied acoustic with a direct sound from the cardioid mic and a controllable stereo image from the bi-directional microphone.

Additionally, because you sent the bi-directional signal post-fader via an aux you only have to move the first fader and the second one follows suit. So although a bit tricky to figure out at first, in the end it's well worth it.

For more recording and microphone techniques, check out the recording page.

Check out the mixing page for tips on mixing your acoustic.

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