Here's a REW Graph of my Matrixed 6-channel stereo mode (i.e. matrixed front wides are partially active in that the mains are in them and the same with the dialog lift effect to the front heights, which equals six speakers playing stereo instead of two, although at reduced levels). I believe I have MRC turned ON as
What it shows is that Audyssey Flat and Reference are identical up until the last octave where they are quite different with the rolloff. However, it's NOT all rolloff, unfortunately.
Flat also has a nasty little upward kick in the curve for some reason that does not exist in the OFF (natural rolloff in room) curve. It's slightly up in reference and both are well above OFF. Reference is a bit more sibilant sounding with some recordings than OFF, but FLAT is awful sounding with high frequency nasties and high sibilance with many recordings.
Given my Carver ribbon speakers upstairs have a natural rolloff in the upper octave, I can't help but think all those years people said "CD sound" was "harsher" than LPs were hearing EXACTLY what this graph shows in the top octave, at least (i.e. much higher levels),although I don't recall hearing anything particularly nasty with headphones, so perhaps it's just that little 6-9kHz bump that does it, in which case I shouldn't blame the mixing guys. However, LPs are also naturally rolled off in the top octave and CDs are flat as a pancake. Most mixing guys in their late 30s or older probably cannot hear above 15kHz worth a damn if not even lower so they wouldn't even REALIZE they were mixing in digital nasties (i.e. too much high frequency content) on CD mixes since they bloody well can't hear it! Well, it's a theory (but my headphone listening seems to contradict it as they should be flat). I never heard it on the Carver speakers because the Carvers rolled off naturally. That reference rolloff, however sounds much better to my ears than flat. But the OFF setting isn't rolled off at all. It's the natural speaker/room response curve. So Audyssey is actually cranking up the natural rolloff to be perfectly flat where it wouldn't be naturally. No wonder it sounds harsh. I'm already sitting fairly near-field in the front row (8 feet from the speakers). I got even worse results the first time I ran Audyssey full range (too much sibilance even in reference mode),but adjusting the speakers and using slightly different mic points helped. I tried bass only to 200Hz, but it didn't help match the speakers anywhere else (i.e. pink noise definitely sounds more consistent between surround speakers with Audyssey turned on, despite all the speakers using identical or near identical drivers).
I could post 2-channel graphs, but they're rather meaningless for the Audyssey settings since Audyssey was set with matrixed sound ON (since that's how it's used normally) so they're not optimized for it. If I got to true 2-channel, I turn Audyssey off (since it can't store two settings).
Also keep in mind, although some mid-range and high frequencies look big, the overall range is still +/- 3.5dB for the most part with Audyssey turned OFF (and the Reference curve is +/- 3dB to all the way to 19kHz and +/- 2.5dB to 10kHz except for that one room dip) up to the final octave where it turns off. That suckout at 700Hz is uncorrectable with Audyssey. I'd need to find a room treatment, which at that frequency could be difficult. Fortunately, it's not something I notice. This room is quite dead of reverb at this point since putting up drapes in key locations (well they were doorways anyway so it also blocks light) and tapestries at the first horizontal reflection point. It sounds a little like a black hole in that room there's so little room reverb compared to how it used to be.
