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This article, Microphone Basics - Part 3, covers the M/S Pair (Mid-Side) microphone placement and decoding techniques. Recording engineers can gain a significant improvement in their results, through a solid understanding of the principles surrounding microphone selection criteria, and microphone placement, relative to a sound source, when they possess a firm knowledge of the design of each type of mic, and intended applications for them.

continued from Part 2

Microphone Basics - Part 3

Finally, let's review the Mid-Side pair, or M/S pair. Here, we will use both a bipolar mic, and a single cardioid condenser. Place these so that the bipolar is facing “across” the source – you want each “hot” side of the mic to face 90 degrees away from the direction of the source. Then, place the cardioid mic, so that it “fills” the centre space between the “sides” of the bipolar, and aim it straight at the source, right through the middle of the bipolar's cross-axial orientation. The objective, is to blend both mic's inputs, so that the “mid” mic (the cardioid) will pick up the “centre” information from the placement, while the bipolar will pick up each of the “sides”, or the room sound, due to its double-faced design and positioning. The issue that presents itself here, is that, because the bipolar's capsules are faced in reversed directions to each other, they are also exactly 180 degrees out of phase with each other (described in other articles on this site), which is the cause of their excellent null-point rejection, however, as such, audio from one side of the bipolar, which mixes well with the centre mic, will most definitely not mix properly, if it arrives at the capsule on the opposite side, because the two sides will be out of phase with each other. So, to fix this, we would have to find a way to “split” the bipolar mic, and reverse the phase of one side of it, so we could get the same in-phase mix from both sides, with the centre mic added in.

The solution? First, take the bipolar mic's signal, and split it into two separate signals, so that each “side” can be connected to its own input channel. Then, reverse the phase of one of the sides, either with the phase reverse switch on one of your input channels, or, if you don't have these, by using a specially-wired cable to switch the “hot” and “cold” components of the circuit. Either way, once this is done, the two sides need to be panned left and right, and the mid mic can then be mixed into the centre, creating a roomy stereo image, plus a strong, 100% mono-compatible centre spot. Balancing the mix of the mid and side signals will “widen” or “narrow” the stereo image presented. This is probably the best configuration for doing solo acoustic guitars, or any soft and dynamic instrument, especially in a nice-sounding room.


By choosing the right mic or mics for the job, and then positioning it/them correctly, the vast bulk of possible problems in recording will be immediately eliminated, allowing you to concentrate on the performance your are capturing, rather than on problems with the sounds you are getting.

 

Go to Part 1 or Part 2 of this article.

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