Mind Stretchers
On Wed, 13 Jun 2012 05:55:18 -0700, KH wrote
(in article ):
On 6/12/2012 8:24 PM, Audio Empire wrote:
On Tue, 12 Jun 2012 04:07:31 -0700, KH wrote
(in ):
On 6/11/2012 6:07 AM, Gary Eickmeier wrote:
wrote in message
...
snip
Then quit asking questions like "where did the information go?". The
spatial information you are describing is left/right - that's it. That
information *is* encoded in the signal. Up/down, front/back, that
information is not present in two channel recordings. You can create an
illusion of depth and height - not the same thing.
I can't agree with you 100% here. Not the "stereo is an illusion" part. That
is certainly true enough, but the part about up/down, front/back, I have to
take serious issue with.
What part of the signal codes for these spatial effects that are not
temporal or level in nature? What am I missing?
Phase differences! They are critical to that perception.
Clearly, speaker
radiation patterns are designed to present this illusion, but as far as
I can tell, it is illusory relative to the recorded signal. Left/right
data is directly addressable since you have one speaker per channel.
I have been making true stereo recordings of
ensembles of all sizes and types, from small, jazz ensembles to large wind
ensembles (concert bands) to full symphony orchestras for many years and I
always use some kind of stereo pair. I either use A-B, X-Y, a coincident
pair
or a single stereo mike in M-S mode. All of my recordings have image height,
and front-to-back layering of instruments. How, you ask? It's simple, true
stereo is phase coherent. It properly captures the phase relationships
between two closely-spaced microphones that tells the listener (on playback,
through speakers) that one sound is emanating from in front of or from
behind
another. It can also tell via these phase cues that, for instance, the brass
are up in risers and the woodwinds are at stage level. Also, in a true
stereo
recording the triangle in the percussion section "seems" to hover over that
section just as it does in a real concert hall situation. These aren't
anomalies or "illusions" as in trickery, these are repeatable phenomenon
that
take advantage of the phase coherent nature of true stereo recordings and is
well covered by papers from Alan Blumlein et al.
Yes, but phase differences are simply temporal differences.
AS I have explained before, they are not temporal in that many different
phases that make up a wavefront can all arrive at the microphone diaphragm
(or the listener's ears) at EXACTLY the same time and yet be different enough
for the ear to reconstruct from the different phases entering the room from
the speakers a three-dimensional aural image containing width, depth, and
height cues.
Perhaps I
should've been clearer in my usage. I'm not suggesting that phase
differences cannot be used to convey some spatial information, only that
speaker radiation patterns must 'mimic' the source sufficiently to fool
our hearing. The depth and height is not really there, in a discreet
sense as is left/right information, front/back/high/low frequency "A"
comes from the same point - thus placement of such signals across a
soundstage is an illusion.
OK, I buy that. Yes, it is conveyed into our room as strictly a left and a
right component. It takes both components, merging in the air in the room
between the speaker diaphragm and one's ears to recreate a three-dimensional
sound field. Our ears do the interpretation of what these phase differences
actually mean. It's the brain that hears "within" that soundfield, phase
differences between the right channel signal and the same information in the
left channel and from those cues constructs the "illusion" that this
instrument is further back than that instrument or that this instrument is
playing from a position higher than that instrument. The info is all there
UNLESS the microphones are too far apart. In that case, I suspect the time
delay between the arriving phase variations from any given instrument or
group of instruments is too long for the ear to properly reconstruct
pin-point depth and height info. That has been my experience, anyway. I admit
that I'm guessing at why spaced omnis don't image as well as a real stereo
pair, but there it is.
Not "trickery", just making use of how we
interpret sound. And many, many illusions are repeatable (visual as
well as auditory). And you can certainly mess that up during replay.
Take a couple of sine waves, out of phase by some degree, and purposely
bounce them off a wall such that the phase relationship changes. How is
that accurate, or helpful, or realistic?
snip
Ignoring preference is as egregious an
error as ignoring the physics or engineering involved.
Especially since the BEST we can do is so far from reality. Audiophiles tend
to gravitate to some smaller part of the whole enchilada and obsess over it
to try to get it right - often at the expense of other parts of the complete
picture. This is 100% preference. One listener obsesses over imaging and
uses
small book-shelf speakers on stands because they image best, while ignoring
the fact that such speakers are often deficient in bass. Another listener
requires that the midrange be right, and the rest of the spectrum be damned.
Still another might be a bass freak with huge sub-woofers that pressurize
his
listening room in what he sees as a realistic manner. To pretend that these
choices that disparate audiophiles make aren't personal preferences, is, at
the very least, an arrogant approach to the question. Were it a question of
one speaker system designed according to the precepts of one man (such as
our
Mr. Eickmeier, here) then there wouldn't be thousands of different models
and
designs of speakers available.
Agreed, although Mr. Eickmeier sees the plethora of speaker designs as
clear evidence that "no one knows" what's going on, thus some "unified
theory" is needed.
That's where he errs. There is no "Unified Theory" simply because no speaker
is perfect, or even close to perfect, so each maker is going off looking for
the ideal "his piece of the puzzle". If perfect speakers existed, there would
be no need for these disparate design methodologies. One speaker design and
one design only would suffice. I don't see why Mr Eickmeier has so much
trouble with that concept.
snip
And where are all these audiophiles complaining about "hole in the
middle"? I've counted exactly one...you.
Hole in the middle? Then your speakers are too far apart. Put them closer
together until the "hole-in-the-middle" disappears. Easy.
Kind of my point. I don't hear people complaining about this "problem"
unless they know nothing about speaker placement.
Exactly!
Keith
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