Re: [LAD] Attenuation of sounds in 3D space

On Thu, 2010-07-22 at 14:15 -0400, Gene Heskett wrote:
> On Thursday, July 22, 2010 01:07:57 pm fons@email-addr-hidden 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@email-addr-hidden-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

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Received on Fri Jul 23 00:15:02 2010