As I've become more comfortable with mid-side stereo recording and matrixing it as LR in post, rather than at capture time, I'm wondering about the ability in various plug-ins to encode LR into MS. Has anyone found this to have practical use?
I've used it on rare occasions, and I do mean RARE, to process the center part of a stereo image. The few times I've done it was when there was something in a track that obfuscates a piece's dialog in some way. If you do it carefully, you can "attenuate" a few frequencies here and there without destroying the left/right image...or replace a tiny segment with surrounding audio (kind of like clumsy manual interpolation) which can help prevent a short loopy sound, because the other "side" information gets left alone. I suppose you could edit the "side" audio instead of the "mid," but I've never done that.
Like I said, it's pretty rare that I do it. But when it works, it's a useful noise reduction trick to have in the bag.
It's quite commonly used in (music) mastering. You can obviously widen/tighten the stereo image, clean up specific "areas" of the mix, and push for more volume (like that's needed!). I've only tried it a few times for interest sake.
Just on a (mid)side note, I'm a HUGE fan of Voxengo's MSED plugin, which allows you to pass your already decoded sound inline through the plugin and work on the matrix again in post. And Michael Maroussas introduced me to the Brainworx bx_solo, which is cool cause you can solo each element of the matrix.
I've done this before to narrow the width of a stereo recording to give it more center focus and mono punch. If you pay close attention to phase, it can be useful sometimes to EQ the M and the S of a signal differently (IE, rolling off some of the lows in the stereo field while keeping the center bass heavy). You could also use it to extract a phantom center from a stereo image.
But now I'm using various imaging tools like Waves Center, S1 Imager to accomplish this. I'm guessing that they might be encoding LR-MS-LR under the hood of these plug-ins anyway.