Ahoy there,
FWIW the Involve decode is actually the Dolby compatible surround mode. We did a bunch of testing with a few Dolby techs and their encoded files, particularly PL-II we did a more even circular decode of their stuff than their own decoder. Involve particularly does well on Pro logic / PL-II stuff as well as regular stereo, and we have found some examples of our decode being more enjoyable (and sometimes accurate) than the deliberate 5.1 mix that came with the DVD release.
Our SQ mode does do a great job with the rear content in PL-II created content, but that's largely because PL-II has an SQ basis anyway. Truthfully though I find the regular Involve mode better anyway as the resulting extraction of ambience is just more...I dunno - I hesitate to say "involving" without my company shirt on - let's just say pleasing. Or encompassing. Yes. That.
~D
Thank you for the response and apologies my delayed reply- Lots of work currently on my plate, and more unexpectedly dropped in after my post.
SQ as you noted is much closer to the Dolby MP matrix. The only x-factor for me is Dolby's somewhat nebulous ("nebulous" as documentation is limited) interior channel. In the original Dolby MP matrix, material encoded with a 90 degree phase shift was designed to emanate from all channels, and most interestingly for me, also was not supposed to interfere with the logic action of most full logic Dolby decoders.
Overture, do you know how your SQ decoding handles this? I know SQ uses 90 phase shifting for hard left rear and right rear, but not much after that.
Before Dolby ever came out with consumer logic decoders, decades ago I had used SQ full logic in my beloved but long gone Marantz 4400 quad receiver on Dolby MP encoded laserdiscs. The catch there (besides the lack of a center channel out) was Marantz's given implantation of full logic decoding. While Marantz's full logic SQ circuitry could occasionally offer exciting separation, it also often introduced very noticeable pumping artifacts and reduced fidelity in a number of areas.
What I know of the given quad formats is from the published equations and interviews of those who designed them. Given I no longer have full logic SQ or QS decoders, the closest thing I could presently test to find out is doing the reverse, by running QS and SQ test tones through a DPL-2 decoder and looking at the wav files in Audition. It was very very interesting (and can eventually provide screenshots if anyone is interested). When it came to the decoding of QS test tones, DPL-2 decoding essentially decoded the rear portion of the QS sound field almost perfectly, while the front part of the sound field showed noticeable leakage / smearing in the three front channels. On the other hand, SQ decoding was the opposite via DPL-2, offering essentially perfect decoding in the three front channels, but the SQ encoded rear sound field channels were smeared, with the exception of SQ's center back, thankfully being the same as Dolby MP's (DPL-1) mono surround channel.
Based on these tests it appears with DPL-2 encoded material, SQ and QS decoding each would bring something to the table, just not all in one system. SQ would seem the most accurate with DPL-1, while QS would correctly decode the split surrounds of DPL-2, while still having leakage issues with DPL-2 in the front.
Thanks again for the previous reply, as I've always found the matrix formats fascinating.