Mid-Side Miking
A rather underutilized approach to stereo miking is MS, which stands for ‘mid-side’. It is an interesting approach, since correctly done, MS will give a variable width stereo image that is absolutely mono compatible. It gives you more control over the width of the stereo spread than any other microphone recording techniques, and it allows you to make adjustments at any time after the recording is finished.
Mid-Side microphone recording is not a new concept. It was devised by Alan Blumlein, an EMI engineer and an early pioneer of stereophonic and surround sound. Blumlein patented the technique in 1933. It works like this: Mid-Side miking uses two microphones – one set to a cardiod pattern and one set to a Figure 8 (also called a ‘bi-directional) pattern. Multi=pattern microphones like a pair of AKG 414XLS or Shure KSM44A work very well. The cardioid microphone (the ‘mid’) should be pointed directly at the sound source. The capsule of the Figure 8 mic (the ‘side’) should be placed as close to the capsule of the cardioid microphone as possible, but pointed at a right angle to the sound source. Traditionally, the front, or ‘positive’ side of the microphone points to the right. As recorded, these two tracks won’t create a stereo image; a decoding process is required.
The decoding of this two channel source involves three channels of a workstation. Assign the ‘mid’ track (the cardioid microphone) to one channel of the workstation, panned to the center. Duplicate the ‘side’ track, and assign each track to its own fader, grouped so that any volume change made to one of the ‘side’ channels will change the other side as well. Pan one the ‘side’ tracks hard left and the other pan the other hard right. Finally reverse the polarity (commonly called phase) on one of the ‘sides’.
There are several ways to reverse the polarity on this channel, depending on how you work. If you’re working with a well equipped console, you can simply hit the ‘phase’ switch on one channel strip. If you’re working in a workstation, you can use a plug-in which reverses polarity, (for example, several of the plug-ins from Waves have an MS decoder as a preset) and on a simple console, you may need to build a patch cable wired with reverse polarity and use this cable to reverse the polarity on one channel.
Once you’ve figured out a method and reversed the polarity, turn up the ‘mid’ channel for the main signal, then bring up the ‘side’ channels equally. The level of the two side channels will determine the width of the stereo signal. But you’ll find that if you listen to the combined signal in mono, the two side channels cancel each other out and only the ‘mid’ signal is present. This makes an MS recording 100% mono compatible, and is one of the reasons the technique used so extensively for broadcasts and for live recording.
If the opportunity arises, spend some time playing with Mid-side miking; it’s a great tool to have in your arsenal.