[LAD] Attenuation of sounds in 3D space

[Ralf Mardorf]

On Thu, 2010-07-22 at 14:15 -0400, Gene Heskett wrote:
> On Thursday, July 22, 2010 01:07:57 pm fons at kokkinizita.net did opine:
> 
> > On Thu, Jul 22, 2010 at 10:35:15AM -0400, Paul Davis wrote:
> > > On Thu, Jul 22, 2010 at 10:29 AM, Chris Cannam
> > > 
> > > <cannam at all-day-breakfast.com> wrote:
> > > > Question that just occurred to me.  I'm very ignorant about spatial
> > > > audio, and although I'm sure several of my colleagues could tell me
> > > > this, I thought it might be sort of on-topic here.  Is it possible,
> > > > or easy, or sensible, or worthwhile, to reduce a B-format recording
> > > > into stereo in multiple different ways in order to achieve
> > > > different subjective "listener position" results when using
> > > > headphones?
> > > 
> > > my limited understanding  is this: the B-format data encodes the
> > > source position relative to some defined point in space. the decoder
> > > can map the "origin" used to define the positional space however it
> > > wants to. whether or not any decoders actually offer any control over
> > > this is another matter.
> > 
> > The first order B-format consists of four signals:
> > 
> > W:      equivalent to an 'omni' microphone,
> > X,Y,Z:  equivalent to figure-of-eight microphones
> >         pointing forward/back, left/right, and up/
> >         down respectively.
> 
> And interesting scenario, Fons.  But it leads this simple minded broadcast 
> engineer with 45 years experience to ask a question.
> 
> 1. How are the signals brought into phase such that electronically, all mic 
> ribbons or diaphragms seem to occupy the same space, just facing in 
> different directions?
> 
> If this is not addressed, then this will lead to some interesting comb 
> filter effects if the signals are not kept from mixing, which they will of 
> course do in the ear.
> 
> Granted, the PV of sound in normal air would require separations of inches 
> till the stuff above high C comes into play, but at the snares and cymbals 
> frequencies, I would have to assume some coloration of the sound from this 
> effect alone.  And of course the same concern comes into play at the 
> speakers since they are generally placed around the listener which in no 
> way approximates the nearly single point reception these mics will hear.
> 
> In my own mind, the placement of a PZ microphone in each of the places one 
> would place the playback speakers would seem to be a superior method, at 
> least for a listener sitting in the nominal center, who will be so 
> overwhelmed by (supposedly not important sonically we are told) the phasing 
> errors that he cannot single out a single largest cause for the lack of 
> realism.
> 
> In my history of electronic repairs for a living over the last 60+ years, 
> one instance of truly hair raising realism took place when I was about 21, 
> and working one of the service benches at Woodburn Sound in Iowa City IA, 
> USA.  I had bought some car parts at noon, and when I left about 6 for 
> dinner, I forgot & left them on the corner of the bench.  Having a key to 
> the back door I let myself into the back door about 8, which was pretty 
> dark by then as only one 25 watt bulb out in the display area was on, and 
> half way to the door to my bench area & right in the door to the front, 
> display room, the Dukes of Dixieland marched by, going right over me.  It 
> seems that Woody and Saul Marantz were out in front, had pulled a 2nd JBL 
> Hartzfield speaker out of Saul's econoline van, setting it just inside the 
> front door opposite to ours in the other front corner of the display floor, 
> along with a Berlant/Concertone tape deck capable of running at 15 and 30 
> IPS.  And the tape was the master that had cut the Dukes then current hit 
> record, running at 30 ips.  SNR was a good 70+ db, and there was no tape 
> hiss audible unless you walked directly in front of the JBL 075 ring 
> radiator tweeters that had been added to both our Hartzfield and to the one 
> Saul was carrying around.  No tone controls, and only a 30 watt Marantz 
> stereo amp., those Hartzfields were then, and may be yet, the most efficient 
> speakers ever made, never used more than 3 or 4 watts/channel to get SPL's 
> that would have done Joshua's trumpets at Jericho proud.
> 
> Truly a total immersion in the sound, from about 35hz to nearly 30khz.  
> Those tweeters could do a fairly good job of reproducing a 25khz square 
> wave.
> 
> It took till I had been introduced to Saul Marantz and shook hands, and for 
> that tape (on 14" NAB reels) to run out before the hair on the back of my 
> neck was truly relaxed.  Saul it turned out was an endless source of 
> technical knowledge sprinkled with BTDT stories.  And needless to say, I 
> did not manage to get that hydromatic transmission I had just stick shifted 
> back together till a day later.  Yeah, I'm a JOAT. :)
> 

As an ape (of course I'm an ape like every human is an ape) and troll (I
don't see myself as a troll) I suspect phasing too, that's why I
overstated argued with the next generation Cochlea-Implant, or needles
in the brain.

Visual 3D, by a surround projection + 3D glasses isn't perfect, but
there is just one picture and not several pictures that needs to be
phase synced in the eye. Perhaps a week analogy.

When having 4 or 8 or more speakers I fear phasing at the position of
the ears. But perhaps it isn't that much. I'll try to listen to
ambisoncs :).

The 5.1 I know sounds bad.

Cheers!

Ralf