‘Mid-Side’ (MS) is a coincident recording system that employs a center mic (usually cardioid) and a side mic (figure eight, bi-directional), right on top of one another.

As it is a coincident system, the signals picked up from the mid and side mic are in phase, and the system is mono compatible once decoded (but not before).

After recording, a mid-side system allows one to mix the center and the left and right signals separately from one another. The left and right signals are decoded from the positive and negative bias recorded from the 2 sides of the bi-directional microphone.

This technique gives the engineer a lot of options to play with the stereo field. In order to create the final left and right stereo channels, the mid and side signals have to be decoded. Depending on the orientation of the side mic, one channel will be M + S, while the other will be M – S.

Mid-side can be a useful technique when recording sound effects as well as it makes for a very compact but versatile microphone setup.

Below is a diagram of a mid-side microphone that contains both mic capsules in one microphone.

image courtesy of bhphotovideo.com
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