Mid/Side mode for multi-channel visualization

[TF3RDL]

Instead of visualizing left/right channels, we can visualize in-phase and out-of-phase FFTs (I'm sure that this thing is used in music production context, but I'd would imagine that M/S spectrum visualization on a consumer audio player would be useful because some songs can sound different when listened in mono and I wanted to know which is "problematic" by looking at Mid and Side spectrums)

Here this could look like on a properly-mixed song:

And here's a stereo spectrum for comparison: