Duel (1971)

Speaking only of the mono tracks on each of these –

1990 MCA Hi-Fi VHS: The same mastering as the 1993 LaserDisc.

1993 MCA LaserDisc [41752]: As is, this sounds muffled, though there is still plenty of high-frequency detail that has been attenuated - presumably rolled off to reduce hiss. With some EQ, it sounds great: -1 dB (bell) at 2500 Hz, q 2.8; +1 dB (bell) at 3130 Hz, q 1.1; +6.2 dB (high shelf) at 4830 Hz, q 1.5; and -2 dB (high shelf) at 13600 Hz, q 2. (Images: 1, 2.) I've applied this EQ to the LD track in the clip below.

2004 R1 Universal DVD - Collector's Edition: Like the blu-ray mono but with additional global noise reduction. 

2015 Universal Blu-ray: The mono track here is a new reduction of the dialogue, music, and effects stems. There is moderate to strong hiss reduction on dialogue (the scene with the children and the school bus sounds especially bad), but less on the music and effects. A handful of the music cues are of significantly higher fidelity than the rest of the film. The effects are typically louder relative to the music, especially in the final five minutes. Some of the crude edits in the original mix have been made less jarring.