Newsgroups: rec.audio
Subject: Re: Carver and the FAQ
From: MATGBB@LURE.LATROBE.EDU.AU (BYRNES,Graham)
Date: Sun, 27 Dec 1992 05:35:37 GMT
Organization: La Trobe University
X-News-Reader: VMS NEWS 1.24

In <1992Dec25.015004.1013@cmkrnl.com> jeh@cmkrnl.com writes:

> In article <11900011@hpmwnpd2.sr.hp.com>,
>  allana@hpmwtd.sr.hp.com (Allan Armstrong) writes:
> > [...]
> > And then there's "Sonic Holography." In college this was considered the
> > ultimate piece of gear to have if you were going to take acid and play
> > Dark Side of the Moon past the clipping threshold of your amplifier. I
> > actually never heard sonic holography. Can anyone report on what it
> > really is? How does it actually work?
> > [...]
> 
> Carver's "Sonic Holography" is an imaging-enhancement mechanism.  
> 
> Suppose your system reproduces a sound that is supposed to be heard as coming
> from only the left speaker.  Your left ear hears it first, and then (because
> your right ear is a bit farther from the speaker) your right ear hears it also.
> So far this is all demonstrable fact.  
> 
> The theory behind "Sonic Holography" says that hearing the sound in both ears
> muddles the soundstage. 

There is an obvious refutation of this. Use headphones. According to "sonic
Hol" theory, the sound stage should be perfect. But unless the recording is
binaural, ie designed to be listened to this way through using dummy head
recording techniques, the soundstage is all in your head... not exactly
realistic.
>         [cut].....
> - When we hear sounds in nature, obviously both ears hear each sound, and 
> there is no "cancelling" signal to help us out.  
> 
> The standard rebuttal from the Sonic Hologram defenders is that stereo
> reproduction is not even close to how we hear sounds in real life anyway.  And
> this point is absolutely correct.  It seems to me that the absolute best that a
> stereo system can do is to reproduce the sound you would hear in a room
> adjacent to the one where live music is being played, with two speaker-sized
> cutouts in the common wall.

NO! This is not how stereo works, at least not usually. This would be the case
if the so-called "spaced omni" mic technique was used, that is two omni
directional mics hung  a few metres apart in front of the orchestra, but this
technique has many problems. More popular is to use a variation on the Blumlein
technique, where two closely spaced directional mics are used, pointing
in different directions, usually supplemented by some other spot mics. See
Lipshitz' article in the JAES (1986?) for an overview.

In any case, what is Carver's argument: stereo is unrealistic, so is sonic
holography, so it must be better?

  Would you expect to hear a realistic sound stage
> (similar to the one you would hear without the wall) from this arrangement?  Of
> course not!
I always have doubts about rhetorical appeals to common sense... which is quite
often wrong. In fact stereo does a pretty good job of reconstructing the sound
field IN A SMALL REGION about the listeners head, without any "tricks".

 It's a lot better than you'd get from just one hole, of course, but
> it doesn't come close to the real thing.  So, since stereo is already playing
> tricks (like exaggerating the level differences between the channels) to fool
> us into thinking there's a soundstage, it should be okay to play a few more
> tricks so that we can be "fooled better". 
> 
> However, my ears and brain must like to be fooled in this way.  I found the
> Sonic Hologram circuit to be very effective at doing "something" to the
> perceived soundstage.  The effect varied widely with different recordings
> (which is only to be expected).  But at no time did it produce what I would
> consider a realistic soundstage. 
> 
> For example, in a simple imaging test where a sound is panned from one speaker
> to the other, the Sonic Hologram made the "image" better defined, but it
> wandered all over the place when it was supposed to simply move from left to
> right and back again. 
Because the effect is frequency dependent. Does wonders for Cello sonatas,
with the highs over here, the lows over there and the mids... comb filtered
by the delay effect.
                    
Mind you, for Dark side of the Moon, who would notice the difference...?
Have fun,
Graham B
(And if more knowledgeable persons wish to barbecue me for my relative
ignorance of mic techniques, go ahead please....)
Newsgroups: rec.audio