My proof is what comes out of the decoders.
I know about phase relationships causing accidental RM/SQ/EV/Dyna back channel information, but SQ back modulations, H back modulations, and UMX front and back modulations don't happen by chance very often.
The SQ left back and UMX center front are 90 degree shifts with the left channel leading the right channel (clockwise).
The SQ right back, H center back, and UMX center back are all 90 degree shifts with the right channel leading the left channel (anticlockwise).
These do not often occur by accident. And when they do happen by accident, they happen at certain frequencies, but not others. Since the parts stay in the same locations with different notes, it indicates that someone put these modulations into those recordings on purpose.
The musical arrangement also gives me clues.
I found all six fundamental SQ modulations on most of my Vangelis albums. The early ones do not have this. "Heaven and Hell" is striking in SQ, with different parts in the different positions. But there are no primary parts at center back, just reverb and pads. I even checked it with my oscilloscope to make sure. There are circular patterns visible that do not happen with ordinary stereo recordings. The same effect is in "Chariots of Fire" and "Opera Sauvage".
I don't have any Klaus Schulze albums.
The Abba albums are different. While both 90 degree modulations are present, the left leads right (clockwise) one is much more prevalent than the right leads left (anticlockwise) one. It is also absent in the earliest Abba albums. This suggests UMX, H, or early Ambisonic encoding, because that modulation is the encoding for center front. But since some of the albums are older than Ambisonic, I eliminated it. Again, I used my oscilloscope to confirm this. It could be SQ, but who would record a lot on the left back, but very little on the right back.
I am not "fixated on UMX," but it seems to be the most likely answer, given the evidence at hand.
I also know that this is not some anomaly in my equipment, because other records don't do it.
There are a couple of other possibilities:
- The synthesizer used in the Vangelis recordings might output quadrature signals from the oscillators for some reason.
- It could be another attempt of the 90 degree phase shift to eliminate the oversized soloist in mono play.
I used to have a magazine article telling how Dynaquad was used in that Beach Boys album. Unfortunately, I can't locate it now, because I was forced to dispose of most of my old magazines when I moved. I saved most of the quad stuff, but this was in either a general purpose audio magazine (e.g. High Fidelity, Stereo Review) or in a rock star genre magazine. All of those hit the dumpster when I moved, unless I marked them for saving due to quad articles or construction projects. Likewise, I had an interview with Meco Monardo in one of the '70s disco magazines.
Polydor may have not released any quad albums, but at that time, they were a subsidiary of a company that signed with CD-4 and made CD-4 albums. My copy of the Tommy soundtrack is on Polydor, and it is in QS.
Try listening to the movie soundtrack albums through decoders, rather than demanding proof from some documented source. The ones that are all music by one group of musicians probably have separate mixes done by the group. But the ones that contain cuts of dialog or action from the film have Dolby Surround, at least on those cuts.