Ugetsu (1953)

1991 Daiei Video LaserDisc [PILD-7030]: The least adulterated presentation of the film's soundtrack, revealing all the shortcomings of the 35mm optical print used for every release except possibly the Criterion LaserDisc. High-frequency detail isn't particularly abundant, but the bass here is impressive. 

1994 Criterion LaserDisc [CC1375L]: This might have been struck from a subpar source, as it's the most muffled by far. The initial clipping in the opening is probably a capture-related issue, but from the rest of the film it's obvious just how bad this disc sounds.

2005 Criterion DVD: Additional hiss and bass reduction compared to the Daiei LaserDisc and a slight ~2 kHz treble boost. 

2012 Masters of Cinema Blu-ray: Similar to the Criterion DVD.

2017 Kadokawa Blu-ray: I was wrong about this one. There is more detail here than on the Criterion blu-ray, but most of the perceived difference comes from the sizable treble boost - around 7 dB at 6500 Hz, q 1.2. This corrects for deficiencies in the source elements and makes some dialogue more lifelike, but it also makes other sounds screechy and of course emphasises the overlying hiss rather unnaturally. The mastering itself also has sections that are lossy transcodes. The Daiei LD in sync with the Kadokawa BD: 1, 2.

2017 Criterion Blu-ray: A bit more noise reduction than the Criterion DVD.

Ugetsu (1953)

I was correct in thinking that the 2017 Criterion blu-ray wouldn't sound anything like the 2017 Kadokawa blu-ray, but I was surprised to discover that the Criterion blu-ray doesn't even use the new sound restoration, despite claiming to.

While Audio Mechanics is credited for the audio in Criterion's booklet...:

The original monaural soundtrack was remastered from a 35mm optical soundtrack print and restored by Audio Mechanics in Burbank California.

 ...the actual track doesn't sound anything like the Kadokawa audio track.

Unlike the Criterion blu-ray of Rashomon, where a superb Audio Mechanics sound restoration was neutered, the Criterion Ugetsu blu-ray audio seems to use a completely different A/D transfer. Not only do the spectrals look nothing alike (the scene-specific fluctuations in high end visible in the Kadokawa spectrum--consistent with the BFI and Kadokawa's presentation of the Audio Mechanics Rashomon resto--are nowhere to be found), but their waveforms also don't remain in sync: after delaying the Criterion track by -20020 ms (the equivalent of 480 frames at 23.976 fps -- the exact duration of the opening Criterion logo), the Criterion track slowly drifts out of sync with the Kadokawa as the film progresses.

The track on the Criterion blu-ray does, however, remain in sync with the track on the old Criterion DVD after taking into account a ~40 ms discrepancy (i.e. ~one visual frame) in the middle of the film. This suggests that Criterion decided to use that mastering (or a less processed version upstream of it) as the basis for their blu-ray track instead of using Audio Mechanics' version. 

Of course, these technical observations don't really matter in the grand scheme of things (other than to suggest that the Audio Mechanics credit is misleading) because the two audio tracks sound totally different. The Criterion is stuffy, muffled, and devoid of all the vibrancy I was impressed by in the Kadokawa track. The Kadokawa/Audio Mechanics may sound like someone's frying bacon offscreen most of the time, but the underlying detail is remarkably lifelike. And that hiss is constant and clean -- it doesn't fluctuate in volume or timbre like an old 78 would. After a minute, your mind tunes it out.