Man of Marble (1977)

This one should make you angry... or at least mildly annoyed.

The audio restoration itself of the original mono mix was no doubt superb. The 5.1 "mix" that was made from it, though...

Somewhere in the authoring process (or possibly a bit before, given how all distributors licensing these Polish classics are putting out the films with multichannel 'upmixes') someone must have thought, "We've gotta make this 5.1! How else are we gonna sell them discs?! Fans of masterpieces of Polish cinema expect 5.1!"

So something very silly was done.

The DMMS BD:
The left and right channels are identical. Fine, not a problem. But they're each about 23 dB quieter than the center channel. That's insane! You can barely hear 'em.

And yes, the center channel was clipped beyond 0 dB and then made quieter, so its peaks are missing.

Otherwise, the center channel contains the exact same audio content as the left and right channels. They're all clearly just the mono track in different states of post-processing. But, the left and right channels then had ~all their bass frequencies removed (and presumably transferred to the LFE - see below). What's left sounds tinny and quite bad.

To verify this filtering visually, we must normalise both tracks according to their peaks before looking at their spectrals. ...But we can't do that very accurately, since, as I said above, the peaks of the center channel have been chopped off. Here's a decent approximation:

Center channel | Left channel    

And we can adjust our scale to look at just the lower frequencies:

...Close enough. You can see that everything from about 220 Hz and below has been attenuated. (Note: rarely anything exists below 20 Hz - not important).

And here's the LFE put against the same (0 to ~300 Hz) Y-axis:

It doesn't contain any information that isn't already in the center channel.

The left and right surround channels don't contain anything, really. If you listen closely enough, you'll hear just the original mono track played extremely quietly. And for whatever reason, the right surround channel is even quieter than the left one. Otherwise, they contain exactly the same information. ...Both are too quiet for us to actually hear at normal listening volumes or to be salvaged with the addition of a massive gain (its noise floor would be too high).

So my best guess is that the center channel presents the original mono mix with the least amount of digital tampering. It's clipped a fair bit, but isolating it is still the best option.