A Clockwork Orange (1971)

Mono:

The UHD blu-ray's AC-3 mono track is exactly the same as the old 1999 Warner DVD's mono track, but 3.9 dB louder.

Recall that the 1991 Warner LaserDisc is veiled and less detailed.

5.1:

The 5.1 mix on the UHD is ostensibly a new mix, although it may well be the old 5.1 mix mastered (very) differently and with changes in various scenes. It's best to just refer to it as a new mix since it's different enough to be designated so.

The centre channel on the UHD is much less rolled-off than the old blu-ray centre channel, and it has a lot more real detail. The old centre channel is veiled and distant, but the new one, although more revealing of distortion (especially across dialogue), is more natural and lifelike. There's a lot of information above 8 kHz that simply didn't exist in the old surround mix's centre.

The left and right channels in the UHD 5.1 mainly differ from the old blu-ray's left and right channels in dialogue-driven scenes: dialogue from the centre channel is now spread ambiently to the left, right, surround left, and surround right channels. This is evident in the spectrals below - you can see that many sections that were empty in the old L/R and SL/SR channels now contain sound. The UHD has surround left and surround right channels that are louder relative to the other channels. The L, R, SL, and SR channels are darker-sounding (bassier) than in the old 5.1.

The LFE of both blu-rays isn't really a 'real' LFE; it contains a surprising amount of high-frequency content, and if one were to listen to it in isolation it often sounds like an ordinary non-LFE channel. The UHD mutes most sections of the movie but is otherwise similar.

Centre:

Left / Right:

Surround left / Surround right:

LFE:

I've read observations from people, some even from professional reviewers, that the new 5.1 track is flawed. Frankly, I disagree; I think it sounds good. Most complain about it being brighter, which I imagine is based on the new centre channel having its high frequencies much less rolled-off. I prefer it. I don't care much for the ambient dialogue now in the surround channels, but the centre channel's 'unveiling' is by far the biggest change here, and it is an improvement.

I wish the mono, on the other hand, sounded better. It's bizarre to read people wishing in the weeks leading to the UHD's release that Warner would include the "old DVD's mono" track, because while it does sound okay, it almost certainly could sound better. A company like Warner should be held to a higher standard and be expected to create a new audio transfer from their assets (which we have no reason to believe have simply disappeared!) after over twenty years since last doing so.

I'm curious if the analogue track on Warner's '80s LaserDisc sounds different.