Optimum

The film was originally mixed in Dolby Stereo (matrixed LCRS). For the 4K restoration, this mix has been transferred from the original magnetic elements and remastered with Lynch's supervision. Unfortunately, the fidelity suffered in the process, with many sections ending up significantly less detailed due to a noise reduction pass. This track has been altered compared to the original, with reverb added to some dialogue, different ambient sound effects, changed panning, and extended bass.

For the unrestored mix, there are two major options, each with its own merits and flaws. The 2001 Paramount DVD, which I would say is the best well-rounded mastering, and the 1999 Japanese LaserDisc, which has noticeably better clarity and high-end detail, as well as better dynamics, but suffers from occasional distortion and has less bass than the DVD.

The LD also has some ambiance buried too low in the mix, and some dialogue panned more to the centre than the DVD. There are no content changes I was able to find. Unfortunately, I don't know what accounts for those differences.

The other available tracks all have more significant flaws. The Italian and Japanese BDs use the same base mastering as the DVD, but with some patching in a few shots. HD-DVD is sourced from an inferior transfer, the same as the Momentum DVD.

The 5.1 remix, originally introduced on the 2002 DVD, and carried over without changes to the 2009 BD is a light and mostly faithful remix, with fairly minimal LFE and surround use, but still potentially worthwhile as the only discrete track.

The DV/HDR grade is tasteful and not overdone. SC has better compression, though not flawless; encoded by FiM, but Criterion also holds up quite well. Both releases claim to be approved by Lynch.

SC has a missing fade that Criterion reinstated.

(preference)

Criterion 4K Blu-ray > StudioCanal 4K Blu-ray. The HDR grading has messed up highlights, so some may prefer the 2020 remastered StudioCanal Blu-ray

Criterion's subtitles seem to be better than StudioCanal's which omits too much IMO.

The 2.0 on the 4K Blu-ray is a downmix.