Recording at home (yours or someone else’s) as opposed to a commercial studio has many advantages, cost, comfort and available time amongst them, but disadvantages too in terms of recording environment. One of the main disadvantages can be that the rooms performances are captured in are designed for living in rather than recording. This can cause some interesting issues when trying to record a stereo room sound with phase issues. Mid/side (M&S) recording can be a great way to deal with these issues.
M&S has several advantages,
- Bulletproof mono compatibility
- Equal focus on the center and sides
- Control over the width of the sound during post-production
- No need for expensive omni pairs
These advantages are very useful in a home recording environment. In an asymmetrical room complex phase relationships can develop, often frequency dependent ones. With M&S you have great mono compatibility with your middle channel. Mic placement still matters but there is always a fallback to pure mono. This can be a take-saver in a room that may sound great but is hard to record in with other stereo techniques like spaced omnis or XY stereo. The mono fallback allows you to make your mic placement decisions based on what sounds best rather than what minimises phase problems.
There are some issues to deal with though. The main one is that M&S can feel intimidating to set up and decode. The fact that the signal needs more done to it than just panning can cause panic. If you are a technophobe do have a go. There are good explanations of how to do it such as this M&S article by Brian Heller.
In summary you use a coincident pair of a cardioid mic for the middle signal and a figure of 8 for the sides recorded to discrete tracks. To decode the signal you mix together the middle and two tracks of the side, one in phase and one out of phase. The side tracks must be at exactly the same level for the technique to work. This is easy in a DAW and grouping the two channels allows for easy manipulation. The relative level of the middle and side signals controls the perceived width of the sound.
Another issue to bear in mind is that M&S can behave somewhat unpredictably in surround formats. The side signal automatically spills into the surround channels. I have met several dubbing mixers who don’t like the recording technique for this reason. In my experience it has worked well automatically, but if it was an issue you can always convert the M&S to A/B stereo to eliminate this issue.
I have had great success with this technique and even if you find it’s not for you all the time it’s a great trick to have in your armoury for any stereo recording situation. Natural room sound adds a real sense of place to a recording. No matter how expensive or clever your reverb unit is it’s not the real world. As long as you have a sweet sounding room to record in room sound is worth using and M&S is a great way to record it.