Mid-side miking is probably the most underused of stereo miking techniques. It sounds complicated, but it’s really a pretty simple process.
Let’s tackle the “why use mid-side” question, and then we’ll get into how to effectively set it up. Mid-side offers the greatest control over the stereo image post-recording. With mid-side, you can control the amount of direct sound (from the mid mic) and the ambient sound (from the side mic) offering exceptional control over the stereo field width.
Mid-side also offers total mono compatibility. With the left and right signals combined, the summed output is solely from the mid pickup mic. And since you typically want less reverb with a mono signal than you’d want with a stereo signal, summing a mid-side recording to mono generates less of the natural ambient reverb from the side mic, making mid-side an excellent choice for stereo recordings that may eventually find their way into being broadcast in mono (like TV broadcasts).
First, you need the right tools. A mid-side setup consists of two microphones — one capable of producing a figure-8 polar pattern (the side mic), and one that has a cardioid pattern (the mid mic). You may also use another figure-8 or an omnidirectional mic in place of the cardioid mid mic. Feel free to experiment, as different polar patterns will produce different results. From here, the only additional tools needed are a recording medium, such as a DAW.
To set up a mid-side stereo configuration, place the cardioid mic where you would normally position it to capture direct sound from the source. Then place the figure-8 mic with its diaphragm at a 90-degree angle to the diaphragm of the cardioid mic. Now inside your DAW, route the mid mic to one channel, and route the side mic to a separate channel, and record.
To fully realize the mid-side you need to make a third, phase-correct track. Copy and paste the track from the side mic into a new track. To make the track phase correct you can use the “invert” command or reverse its phase or polarity in your DAW’s software. Pan the mid track to the center, pan the “side” track to one side, and pan the inverted side track to the opposite side. Then use your DAW’s “group tracks” (or whatever term your specific DAW uses) to set it so that both the original and copied side tracks change volume at the same time. Adjust the volume on the side tracks to add more or less stereo information to your tastes.
Mid-side miking is especially useful for miking small ensembles or any situation where a good amount of room sound is desired.