On Thu, 2010-07-22 at 14:15 -0400, Gene Heskett wrote: > On Thursday, July 22, 2010 01:07:57 pm [email protected] 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 > > > > > > <[email protected]> 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 _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
