A Clockwork Orange (1971)

The 5.1 remix (the only mix on the blu-rays) is a legitimate, discrete mix that generally has much better fidelity than the original mono mix.

But it's far from perfect. For whatever silly reason, ambient sound has been added to EVERY scene that played mostly silent in the original mix, so scenes that don't contain music now have what sounds light street noise and wind underlying them. Bizarrely, this applies to both outdoor and indoor scenes.

The music also seems far too loud in the remix relative to the dialogue.

The original mono mix was issued in 1991 by Warner on LaserDisc and later on DVD (R1, R2, R3, and R4). The LaserDisc doesn't sound very good. Its high frequencies are attenuated and it sounds like it's an analogue generation removed from the old R2 DVD I was able to find.

The mono track on the DVD reveals that the original mono mix is a more cohesive, well-balanced mix and I prefer it overall despite its generally inferior sound quality (music, mostly). It has some crazy bass! If it weren't for the unusually heavy degree of compression applied to it (no doubt inherent in the mix itself), I wouldn't hesitate to call it truly excellent. Again, its music levels are better balanced relative to everything else, and the entire thing just sounds right.

The PAL DVD also plays at the correct pitch and tempo, so I assume it's an NTSC-to-PAL convert (I didn't bother to verify this).