It's a Wonderful Life (1946)

1985 3M LaserDisc: Sounds very dupey; subpar analogue source.

1987 Criterion LaserDisc: Decent; extremely clean and free of distortion, but it doesn't have much bass detail. Segments with music sound very anaemic. Certainly not sourced from the best extant element(s). This edition has no digital track, contrary to what its LDDB entry says.

<1991 Republic Pictures LaserDisc: Generally the most detailed of any of these editions, but also riddled with distortion in many scenes. (I think I have a high tolerance for noise, but even I think it's intrusive!) Very likely an untouched transfer without any mastering work. It's difficult to say whether the distortion is due to transfer issues or if it was all (pretty impressively) attenuated for later editions. This was probably released in the late '80s.

1991 Republic Pictures LaserDisc (45th anniversary): Distortion-free and sourced from the best extant element(s), this is probably the edition that would sound best to most people. Unfortunately, some high-end detail has been removed and can't be recovered with EQ – the previous Republic Pictures LD sounds noticeably more immediate in many places and even the Criterion LD sometimes sounds better in scenes with just dialogue.

1992 IVC LaserDisc: Very dupey-sounding, even more so than the 3M LD. Probably sourced from some nth generation Japanese print they had lying around.

1996 Republic Pictures LaserDisc (50th anniversary): The first LaserDisc to sound like a modern archival release – digitally scrubbed and muffled. It sounds like the 1991 LD but with more hiss reduction and is nearly identical to most of the later DVDs and the StudioCanal blu-ray. 

2004 Paramount R4 DVD: This (unique?) Australian DVD sounds different to the R1 DVD I compared; it's basically the <1991 Republic Pictures LD but with slightly worse (rolled off) EQ. (To make this disc easier to identify: it has a tonne of subtitle options, including Hebrew and Icelandic.)

2006 Paramount R1 DVD: See here. It sounds like the 1996 Republic Pictures LD. I remember that all the R1 DVDs (released in different years) that I checked years ago shared the same audio track.

2009 Paramount Blu-ray: See previous post. By far the worse sounding version, with some additional downstream noise reduction applied at the ~authoring stage.

2013 StudioCanal Blu-ray (Germany, colourised): See previous post. Identical to the 2006 DVD but lossless.

2019 Paramount Blu-rays: The audio tracks on the UHD and non-UHD blu-rays of the 4K restoration are identical. They sound like the StudioCanal blu-ray but slightly brighter -- whether from EQ (post-hiss reduction) or from less hiss reduction in the first place, I don't know. I think it does sound a bit better, but they're similar overall.

Many thanks to the person who captured all the LD tracks and sent them to me, without whom I never would have produced a comprehensive analysis.