Interesting points all...
How close to reality do you have to get for something to be real? The first time I heard someone talkig about suspension of dispelief it was a cartoon animator talking about e.g. running hard to get back to the cliff edge you'd just run off before you started falling. Clearly this requires a fair stretch of the imagination. However, I suspect a far smaller suspension is required to believe a) a 25-year old bimbo is still in high-school and b) she packs a punch sufficent to see off a load of vampires and demons - I certainly know a few well capable of believing that, and I'm sure I could be persuaded to investigate with the young lady in question (purely in the interests of scientific research

). (My...this calvaldos is good). Now where was I...oh yes hifi....
Pursuing the psychoacoustics a bit further, I think an important point is the accuracy and adaptability of our audio memory. I think I have a particularly inaccurate one (e.g. I find it very difficult to be consistent in comparing the sound of a system with one cable vs it with another :newbie: , unless I can do back-to-back switching) - or at least one that is fairly swayed by what my brain is telling it. I have now removed most of the impedimenta to me believing that what my system is telling me is real - unless I hear the real thing in fairly close proximity, when the system's abject failure is quite obvious. The following day though it starts sounding pretty good again.
Tying this in with the earlier point about the piano - a few weeks ago I was about 8 yards away from a piano palyed by Maurizio Pollini - i.e. the kind of distance reproduced by the hifi facsimile. The energy in the real attack was quite deafening - and playing some of the same pieces when I got home (about 1.5 hours after the concert finished) it was staggering how blunted the reproduced piano sound was in comparison (but even if I'm not a bleeding-edge merchant it's no slouch - sideshowbob jumped out of his skin when he heard the Chopin Etude I'm talking about).
Trying to fit a 200 piece orchestra in a 4x3m room? While this is clearly a major problem/feat of disbelief-suspension, I think the important point for me here is the ability to project the image from the speakers back through the wall behind them. Maybe again it's a matter of the brain fitting what it hears into its expectations, but I hear an orchestral recording more distant than a solo recording, such that the apparent width of the orchestra scales appropriate to the angle subtended at the listening position by the speakers. With a system able to do soundstage depth, the orchestra then goes happily through the far wall. Of course its perfectly possible for the recording engineer to mess things up (I have some very 1-2D sounding recordings). I guess this is the same point as sideshowbob's (which has just turned up while I've been writing this).
Which leads on to Bottleneck's point about miking. There does appear to be a religious divide here - mike everything separately, or use a minimal set of microphones. Mercury Living Presence reckoned to use no more than 3 mikes - and it comes out pretty well (although the sound of the one or two CDs I've heard is a bit on the historic side). I've also seen concerts (e.g. LSO Live) miked up with about 3-dozen. I feel the most realistic results would be achieved with a single crossed pair set somehwere above the central stalls, with maybe the odd touchup from the other localised mikes only when necessary. Since this is nothing more than gut feeling it could be way off beam though.
There's also an important point to consider about mastering: if the expectation is for a system with low resolving power, channel separation etc then the engineer is going to put in greater spotlighting/stereo spread etc, which will then sound dreadfully artificial on a system that can do the resolution thing.
The most insurmountable problem I see though is reproducing the hall ambience. I've a reasonable number of live recordings where this is done wonderfully (e.g. Friday Night in San Francisco - Lee summed it up nicely when he said "I feel like I'm on the stage and the audience are all 'out there'). This is also why I like live orchestral recordings: the little coughs etc and other ambient queues from the audience do give a feeling of a huge concert hall. However that's all from around the region of the speakers back and through the far wall. What it doesn't do is give the feeling of space behing and particularly above you, which is what you get in a real venue. The TACT system tries to remove the unwanted reflections that say "this room is 4x3, tough", but I'm not at all convinced it can do the full ambience thing. Maybe this is where properly done surround would help. The only time I've tried this though was at those Classe/B&W demoes, where I've never been in the right place to get the proper front-back balance (which I see as one of the big problems with surround hifi), and so didn't really get the right effect. (The "put-you-in-the-middle-of-the-band" effect that the Meridian people did was a complete turn-off though.) So it's all round to Merlin's when he gets his TACT surround in - and he said he was done with box-swapping

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