The Mellotron Group

from Wikipedia (i'd read this elsewhere several years ago):

In 1978 the album was remixed due to deterioration of the master 
tapes. The original 1967 stereo mix, which is generally considered 
superior by fans, has never seen a CD release. All CD versions, even 
remasters, use the later mix. However, the 1990 greatest hits 
package "The Story Of The Moody Blues/Legend Of A Band" CD 
compilation, seems to contain the original mix of "Nights In White 
Satin".

The ways in which the later mix departs most noticeably from the 
original are:

After the orchestral intro, "Dawn Is A Feeling" begins more abruptly, 
and there is less echo on Mike Pinder's vocal on the bridge, making 
it stick out. 
The orchestral intro "Lunch Break" goes on about 20 seconds longer 
before fading out. 
The transition from the band to the orchestra in "Forever Afternoon" 
is cleaner, making it almost seem as if one flute is playing 
throughout. 
The bridges to "Time To Get Away" have John Lodge singing alone; all 
the backing vocals on that part have been lost. Also, at the end of 
the piece, the words "Evening, Time to Get Away" are repeated only 
twice where they were repeated three times on the original mix, and 
the mellotron overdub, which was essentially the same as the one in 
the middle section, is absent. (In the quad mix, the mellotron is 
also missing from the middle section.) 
The piano in the instrumental sections of "Sunset" is gone. Also, the 
reverb on the last word ("Through the night") is very different. 
The backing vocals on "Twilight Time" are heard through the entire 
song instead of only coming in at strategic points. 
After the :13 orchestral prelude to "Night In White Satin", the 
rhythm section (Moody's instruments) comes in right on time and in 
step, following the correct meter of the orchestra. This seems to 
correct the seemingly "off-step" segue of the two pieces on the 
original mix. 
There seems to be a noise-reduction filter overlaying the rhythm 
section of the original mix, resulting in a more murky, ghostly sound 
quality. 
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also, if you have a cassette copy from the 80's "Peak Hour" is almost 
twice as long (a goodly section of the tune is repeated).

i like the newer mix as it cleaner but the original mix, overall, is 
my fave.