Originally Posted by RWetmore
Huh??? You most certainly do not need to separately mic the whole orchestra to capture components above 22khz.
First off, what does "above 22 KHz" mean. Does it mean capturing from 22 KHz to 23 KHz? No, it can't be just from 22 to 23 KHz because that would be like 1/20 of an octave which is perceptually insignificant even at 5 KHz.
How about from 22 KHz to 44 KHz with negligable losses? That's a full octave and would be signficiant other than the (disputed) ultrasonic means can't hear, thing. So for the purpose of discussion, we want reasaonbly flat response up to 44 KHz, right?
But we're back at the point where the losses at 44 KHz over concert hall distances are pretty impressive. I mean like 10s and 10s of dB being lost. You'd be very unhappy if this was going on at say 10 KHz, and isn't the idea being proposed that losses at 20KHz are something like as signfigicant as losses at 10 KHz? Maybe less, but still like 1/4 or 1/3 as important?
First off, the dimensions of a seated full orchestra may surprise you. I previously mentioned > 100:1 loss of HF information over a 20 meter or 60 foot distance.
So how large is the onstage seating area in a good sized concert hall? The answer may surprise you - 60 feet wide (proscineum opening) and 50 feet deep (proscineum to back of shell) with maybe a 10-15 foot distance from the proscinium to the lip of the stage and another 6-10 feet to the first row of seats. BTW, did you notice that the percussion instruments tend to be parked towards the back?
Oh so you don't want to sit in the front row? Well add maybe 3 feet or more for every row back.
Now check out how people minimally mic orchestras. The first row of mics are probably in the area between the proscinium and the lip of the stage. There are probably some ambience mics suspended above the seating area, maybe 1/3 or 1/2 of the way back. All the mics are at least 10-15' above the floor.
So, that 60 foot number is pretty much ballpark for minimal micing of the orchestra. And, its more like 100 feet to a good seat in the house.
Again, presuming that ultrasonic overtones are audible, if you close mic with a good wideband mic (very rare and expensive BTW) then the mic is going to get an abundance, as in 10s of dB more ultrasonics than a person would get when seated in a good seat in the house. If the recording is a DACD or high sample rate DVD-A, then the medium is going to reproduce this gross excess of ultrasonics quite well. Finally, you've seated yourself 3-6 feet from your speakers and exactly on-axis so again the losses for ultrasonics are going to be minimal.
But didn't we just figure out that our close-miced recording is going to have 10s of dBs more ultrasonics than a really good seat in the house?
Why isn't it that people with really good speakers aren't running out of their listening rooms screaming having been deafened by this probable gross excess of ultrasonics on their close-miced SACDs and DVD-As?
The reason is quite simple. The ultrasonics are truely inaudible and we can't hear whether there is 10 times too much, or 10 times too little or that they are just right.
Hey, we're still having way too much trouble getting things right *below* 20 KHz. Let's not make this Hi Fi thing even more complex than it already is!