I've read that the box set sounds better than the individual remasters. However, I alwats though they were the exact same thing. In fact, I can't image they're not. I'm sure there is plenty of insight on these boards.
Don't forget you get two extras song on the CODA box set. TRB was one and can't remember the other off the top (White Summer/Black Mountain Side?). I don't usually listen to CODA so memory is a little fuzzy.
I've learned to take the release dates listed on iTunes with some skepticism. I have yet to find one that is accurate. My suspicion is that the release dates they use are the dates things are released in the iTunes store. I always check additional resources if there is a question of release dates to influence my purchase.
As for quality of the complete recordings set, I'm torn myself and looking into this. I was all set to buy it, but then I came across a review mentioning the most recent remasters as superior in sound quality. As far as I can tell, only The Song Remains The Same and Mothership have been remastered in this manner. I have found excellent reviews of the sound quality and at the same time complaints about editing out beloved parts of songs (not to mention entire songs), particularly in the case of The Song Remains The Same.
My reading says the Led Zeppelin tapes were only converted to digital twice -- once in 1987 by a guy named Diamante (considered by some to be the best conversions because they were the original album pressing EQ's), and again in 1990 by Jimmy Page and George Marino. The Marino conversions were subsequently remastered to have more bass and treble and more compression, i.e. volume, to take advantage of the dynamic range possible with CD's. The Collector's set and the subsequent individual CD's are from the same Page/Marino sessions.
Complete remasters are the same as the original box-set. George Marino went over the whole catalog and the band picked which songs would be on box sets 1 and 2. Nothing's been done since except the work on Mothership.
The important thing is that with Mothership, the move to downloadable MP3 format meant a compressed file. The remastering was done to make sure that the best parts of the musical dynamics weren't the ones compressed, hence lost. A simple conversion to MP3 could turn out like crap when you leave it to the computer to interpolate the file, thus Shirley and Page selected the bits that would shrink the file size so it still sounded as best as could be presented.
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