“Another Door” is my favorite track on the album (I love the interplay between the acoustic guitars and piano) and the quad mix is a revelation compared to the stereo. There’s an additional acoustic guitar part in right rear that I don’t recall from the stereo cut, and during the chorus there’s a very cool high harmony vocal isolated in the left front speaker. It's worth picking up the quad album just for this track, IMO.
Interesting addendum to this review: I received the quad reel in the mail this morning and listened to the whole thing as it recorded into my DAW. Everything's sounding great--just like the CD-4 LP, only cleaner and more discrete--until I got to my favorite track, "Another Door". For whatever reason, just this song appears to have an
entirely different quad mix on the reel. At first I thought there might be a swapped channel, but then I listened to each channel individually on the PC and noticed some key differences in the way the instruments are panned. Samples of the first 30 seconds, rear channels only, from both the LP and the reel are posted below.
CD-4 LP:
Lead Vocal: Front Center (with some bleed and echo in the rears - possibly a CD-4 separation artifact?)
Harmony Vocal: Front Left
Drums: Front Right (and maybe 10% volume in rear right - again, this could be the limitations of my CD-4 setup)
Bass Guitar: Front Left
Piano: Rear Left
Harpsichord: Rear Right
Quad Reel:
Lead Vocal: All Four Channels (dead center in the fronts, but in sort of echo-y stereo in the rears. It's hard to describe the effect)
Harmony Vocal: Rears
Drums: Rear Right
Bass Guitar: Rear Center
Piano: Fronts (sounds like a stereo image with the higher keys on the left and lower on the right)
Harpsichord: Rear Left
Interesting, to say the least. I've never heard the Q8, so there may yet be another version. How do you explain this?
@steelydave theorized upthread that this quad mix may have been done back in 1971 and sat unreleased until Elektra committed to a quad vinyl format. Maybe there were several attempts at the album - and when it came time to compile the 4-channel masters and begin production on the quad LPs/tapes two years later, staffers may have accidentally picked an alternate/rejected mix of this song. If that's actually what happened, I'm not sure which was the intended version - I think the CD-4 mix fits in better with the rest of the album, but both have their pluses and minuses.