[Gary Eickmeier]

"Audio Empire" wrote in message
...

True, but since the microphones, in a correctly miked stage performance,
are
up on the stage (or hanging over it), that is the perspective that you are
capturing - "the closest seats". I have some British made AmbiSonics
recordings where the mikes are quite distant from the stage. The effect
isn't
very appealing

Not quite. As I alluded in one of my quaint analogies, we do not perceive
the sound from the perspective of the microphones. We place the microphones
closer to the soundstage than a good, typical listening position, not
because we wish to hear the concert as if suspended nine feet above the
conductor's head or two feet from the lips of the mezzo soprano, but because
when we play it back we will be playing it from speakers that are placed at
some distance from us, so that the perspective becomes correct again. As I
have also said, this is the opposite of binaural theory, in which you want
to place the head at a good listening seat, because you are going to be
capturing just that perspective, and recording the entire ambience of the
original hall from that position.

In stereo, a field-type sytem, we are going more toward the capturing of the
direct and early reflected sound from the region of the proscenium, and just
enough of the reverberant field to give the "flavor" of the original hall,
but realizing that it will be mixed with the listening room acoustics
because of this distant placement of the speakers. And this is not an
error - it is intended that both ears hear both speakers, and that we hear
the total sound field from the speaker/room interface. THAT is the area that
needs to be studied further, as I have suggested. That is, how to make the
speaker/room interface sound more like the live field than typical "hi fi"
has done so far.

You are also correct that in a concert, the members of the audience are
not
aware of the hall acoustics per-se as they blend-in as part of the
performance, but believe me, they'd notice if they suddenly went away!

Yes - and here we also run into large vs small room acoustics. In the large
room, the reverberant field is much smoother and all around you. This is how
we perceive the timbre of the instruments - the total sound power output
combines in the reverberant field so that we hear what it sounds like in its
full radiation pattern. It is the early reflected sound that gives the
spaciousness and separates the good halls from the bad. The direct field is
but a very small portion of the sound heard at a good seat.

It is the opposite in hi fi. In a search for "accuracy," we attempt to
direct the recorded signal all toward our ears, and diminish the nasty
reflections from the listening room - which already has no appreciable
reverberant field! The difference in these two sound fields is obvious. Some
of us have buttressed the missing reverberant field at home with surround
speakers on delay, so that is addressed with some degree of "modeling" the
repro field after the original, but the frontal soundstage shape has been
all but ignored.

The recording contains all of the sound I have just described - if done
right - but in the reproduction we force it all from the same direction as
the direct sound, which is an error. The effect of a spatial broadening of
reflected sound has been well reported in the literature, but not tied to
any particular reproduction theory as to how it can cause the early
reflected sound that was recorded to come from a more correct set of
incident angles. Keith can't understand how reflecting some of the output
can decode the early reflected contained in the recording and separate it
from the direct part that was recorded, but I am reporting that it can and
does work. The direct sound part undergoes a harmless image shift toward the
side and rear of the speaker, while the later and more sustained tones take
on a spatial broadening effect that can make the recorded early reflections
seem to be coming from the appropriate wall of your room. A greater
impression of depth of image is caused by the simple fact that the speakers
are pulled out from the front wall into free space, and the reflected sound
comes from behind them. All of these effects have been reported in speaker
tests in the magazines, but they have no idea what causes them.

Gary Eickmeier

PS - I have to make a trip up to Michigan for a week, and not sure I will be
able to respond to any additional comments on this in Google Groups, so may
have to delay for a week if anyone is interested.