h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

This is an interesting Guide entry. It opens up the whole area of "post-production", which I understand is the practice of tarting up an otherwise finished product to make it sound better, add sounds that weren't originally there, and taking out things which are out of place, (like the inconvenient background rumble of traffic noise from the nearby motorway that wouldn't have been there in 1800 and which coems across just loud and clear enough in your film adaptation of Jane Austen)

I wonder about how far this goes and how prevalent it is. For instance, watching "The World at War" for the umpteenth time, I suspect a lot of the original WW2 film has been "enhanced" with effects from the sound library. For instance, obvious amateur footage taken on the move by a German tank crewman with a hand-held super-eight camera (but which perfectly captures the feel of the Blitzkrieg into France) somehow also manages to have a soundtrack of the roar of the engine and the rattle and creak of tank tracks. Surely not many cameras available to the amateur enthusiast in 1940 would have allowed for sound recording?

Similarly, grainy and slightly out-of-focus film footage taken in combat still manages to have a FAR better soundtrack, right down to the zip and ping of individual bullets, than the picture quality would allow for: and if the photographer has picked up this amount of weapons noise, why aren't the shouts of the participating soldiers audible, even faintly? It's like having the film in mono and the soundtrack in stereo... another example is what surely must have been film-only footage of the London Blitz, where a wall collapses on cue to a roaring and rumbling noise, but there is hardly any crackle of the raging fire causing it to fall.

Somebody, I think, was seeking to improve on the original footage by adding relevant noises from the sound library?