But wait- there's more!
It seems that the mediumrecords guy wrote to the Webmaster of the Danish site he took the clip from to ask what the source was, and was told that it came from the TV movie
Rudy! The Rudy Giuliani Story.
I hunted up a copy of the DVD through Amazon, brought it to work (we have DVD players in the lounges, while I don't even own a TV) and started fast-forwarding it from the beginning.
The clip in question turns out to be in chapter 7, at about 37:00 into the movie, and the audio the mediumrecords guy thought proved the use of explosives is there as well.
This explains some things about the video clip as seen on the Web.
The "10:28" time title- the producers used the Trinity Church footage of the collapse of WTC2 (which fell at 9:59) as a stand-in for the collapse of WTC1 (which fell at 10:28).
The reverberation on the second "explosion"- the sound designers were looking for SFX suitable to suggest the sudden breaking of a massive structure (after still more listening I'm leaning to the opinion that the SFX are actually thunderclaps rather than explosions, obtained from some commercial SFX library) and added a load of digital reverb to the second one, which suited their sense of the dramatic but also made it obvious to an experienced listener that the audio was not authentic.
I've also noticed some things which suggest that the sound/picture sync of the clip on the Web and that of the original DVD are not identical. Pulling everything together so that I can do good direct comparisons of the two is a bit problematic (the video from mediumrecords won't play with sound on the Macintoshi at work, which lack the AAC codec, I have no TV or DVD at home and only a dial-up connection there and both of the studios where I work are uncharacteristically busy for December), but I hope to be able to give that proper scrutiny sometime in the near future. While it's possible that the DVDs sold in the USA and in Europe have different video edits, it's also possible that someone has monkeyed with the audio before putting it on their Web site.
As of now, one thing can definitely be said of mediumrecords' "analysis":
He got fooled by a Hollywood movie!
