Cinderella (1950)

Mono:

1995 Disney LaserDisc [4964 CS]: The mono analogue track sounds very good. It's exceptionally clean, with very few ticks or pops, and has no hiss reduction. Although it sounds comparatively bass-anaemic next to the blu-rays, it is actually quite detailed - continue below.

2005 R1 Disney DVD: This sounds poor. Extremely strong noise reduction and overly trebly. 

2012 Disney Blu-ray: The mono track here seems like the DVD mono but with significantly less hiss reduction and slightly more natural EQ. But it's still quite NRed, especially during quiet scenes which sound weird and warbly. Both this and the DVD mono may be new mono reconstructions created from the dialogue and music/effects stems, but as there are no new effects, whether they are/aren't means little. The blu-ray mono has an annoying distortion (remnant high-frequency artefacts that escaped the noise reduction applied to the frequencies just below) that isn't audible on the LD.

The blu-ray mono gives the impression of having more detail than the LD, primarily due to its greater bass; however, after playing around with the LD track, I was able to EQ it to resemble the blu-ray quite easily: +6 dB at 250 Hz, q 0.9 (low shelf); +6 dB at 5400 Hz, q 1.0 (peak); +6 dB at 9000 Hz, q 2.8 (peak).

Stereo:

1992 Disney LaserDisc [PILA-1125]: The 2.0 PCM track sounds terrible - very strong noise reduction. Horribly muffled.

1995 Disney LaserDisc [4964 CS]: The 2.0 PCM track has less noise reduction than the 1992 LD, but it's still murky.

Multichannel:

The 7.1 track on the blu-ray and the 5.1 track on the UHD seem like the new mono track surrounded by the mono music stem - i.e. the mono track from the blu-ray occupying the centre channel, with mono music spread (in varying amounts of reverb) between the surround left, surround right, back left, and back right channels. The front left and right channels occasionally possess voices, simulating  directional dialogue.

For the images below, I've volume-matched the centre channels at 1 kHz to the blu-ray mono to show how alike they are - virtually the same, apart from select moments in the centre channels that dip in volume when said dialogue shifts to the front left and front right channels.

The UHD 5.1 has more reverb on its surround channels than the blu-ray 7.1. It also looks like a lossy transcode. 

7.1/5.1, L

7.1/5.1, R

7.1/5.1, C

7.1/5.1, SL

7.1/5.1, SR

7.1/5.1, LFE

7.1, BL & BR