When most people think of studio recordings, a simple recording with a microphone in front of a sound source usually comes to mind. A single microphone in front of a guitar, or in front of a vocalist recording their sound to later produce. However, this is not always the case. Stereo recording is also a common technique used in recording audio, and allows for a wider range of sounds to be picked up from a multitude of sources in a certain direction, allowing for a wider sound image to be heard on playback and manipulated when editing. Your typical, normal stereo setup would require an identical pair of mics set up in an XY pattern, like this;
This pattern traditionally is setup to mimic your own ears and “relies on the time delay of a sound arriving at one input milliseconds sooner than the other to localize a sound within a stereo field.”  (“Mid-Side (MS) Mic Recording Basics | Universal Audio”, 2018) and this concept works well as long as it is set up correctly and as long as both mics are evenly spaced and are either in a pair, or are of the same make or are very similar in make.
This is where the Mid-Side or MS technique comes in handy. This technique allows more control over the width of the stereo image and also allows for changes to be made to the width of the sound after it has been recorded where the XY technique does not.
To successfully setup and create the MS technique, two microphones will be needed. Unlike the XY technique, where a matched pair or two microphones of very similar make are needed, the MS technique requires two microphones of any kind, with the only requirement being that one must have the ability to record in a figure of 8 polar pattern (pictured below )
The ‘Mid’ microphone is set up facing the centre of the sound source. This microphone is set to the polar pattern of cardioid, and can range from dynamic microphones such as a shure sm58, or a condenser microphone of any kind with a cardioid polar pattern. The side microphone is required to be set up in a figure of 8 pattern and therefore requires a mic with access to this. This microphone is aimed 90 degrees off axis to the sound source. It is necessary that these microphones be setup practically on top of each other to avoid phase issues. Predominantly, the mid mic is setup on top with the side mic underneath, close, but not quite touching the mic above it (as pictured below ).
Now that the microphones are set up in their correct positions an extra step inside the DAW (Digital Audio Workstation) is required to enable the MS technique to work. To correctly hear a stereo image with this technique, the side microphone must have each side’s signal split onto two channels. From here, one side must be completely phase flipped and each channel must be panned hard left and hard right respectively. The result will enable you to hear what both sides of the figure 8 microphone are hearing. This step is critical in the successful application of the MS technique. If you’re interested to find out some of the things that can go wrong otherwise, have a read of my studio roundup blog where I go into depth about a problem I had myself when forgetting this step.
Anywho, now you have 3 channels of audio, a middle channel, a left channel and a right channel which must be balanced to recreate a stereo image and this balancing is completely up to you. If you are recording an orchestra using this technique and the instruments on the right hand side are a little loud and you want to let in some more of the instruments on the left, simply take some volume out of the right hand side or add a little more to the left and the stereo image and feel of the right hand side is lesser than the left.
 Auld, R. (2018). Recording the Classical Guitar: Stereo miking techniques for capturing a tricky instrument. Recording Magazine. Retrieved 5 April 2018, from http://recordingmag.com/recording-resources/recording-info/recording-the-classical-guitar/
 Mid-Side (MS) Mic Recording Basics | Universal Audio. (2018). Uaudio.com. Retrieved 5 April 2018, from https://www.uaudio.com/blog/mid-side-mic-recording/
 MICROPHONE DESIGN. (2018). thesoundscoop. Retrieved 7 April 2018, from https://thesoundscoopblog.wordpress.com/2015/01/10/microphone-design/
 UA WebZine “Analog Obsession” December 05 | The Mid-Side (MS) Stereo Microphone Technique. (2018). Uaudio.com. Retrieved 7 April 2018, from http://www.uaudio.com/webzine/2005/december/text/content4.html