Mixing 4-channel files from Zoom H2 into Stereo

On my Zoom H2, I accidentally recorded 4 channels instead of stereo. I’d like to use my Audaicty 2.1.3 on Windows to mix it back into stereo.

The files I have are filenameMS.wav and filenameXY.wav
I’m not sure if that meant the mic switch was set to “4 channel” or “Mid-Side”

Any advice on how to mix these down?

If you only used two microphones, you can just ignore the mid-side file. The XY file should be normal stereo.

Mid-side is the L+R sum (mid) and the L-R difference (side). It’s the same information and it still uses 2-channels, but it’s in a different format. It’s simple math and formats can be converted back-and-forth losslessly.

There are microphone techniques that allow you to record the L+R and L-R directly on a regular stereo recorder, but it requires a figure-8 microphone to pick-up the left & right sounds out-of-phase, while rejecting the center. Then at some point it gets converted to regular stereo. M-S allows some “tricks” such as equalizing the “center” differently than the left-only and right-only sounds.