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Old 18th October 2006, 02:04 PM   #11
SY is offline SY  United States
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soongc, Ambisonics is different than other ambience schemes. The space it creates is not artificial or even derived, but built into the coding. It breaks out of the L-R-back-front paradigm in a very profound way. Peter Fellgett was way ahead on this one.
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Old 18th October 2006, 02:49 PM   #12
soongsc is offline soongsc  Taiwan
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Heater: I think I have just not seen any math that correctly describes preservation of the sound field. If seen some things show show you some fance 3D patterns generated by math, but none that describes the actual math from performer mic location to playback speaker lisenter location. If I have misted something, please by all mean point us in the right direction. I did all the search I could, but nothing meaningfull, only what normally you would see in promotion talk. Is there ans AES publication on this? If there is I would be interested in reading it.

Basic geometry shows us that in order to truly reproduce 3D you need at least four speakers with one speaker elevated from the rest of the three to recreate height allocation. This is the same way with GPS.

SY: I've always heard this kind of talk, but no real convincing expalantion or math. This just puts the dicussion in the "cables differences" category. Perhaps Peter Fellgett can point us to some information that will shed some light?

Edit:
I would like to refer to Wireless World November 1982 "Binaural Recordings and Loudspeakers" by J.H. Buijs. Now this article explains Binaural Recording and playback in a very understandable manner. If there is something on Ambisonics like this, it would let everyone understand how good it technically is.

Of course, if there is anywhere I can go to in this neck of the woods to have first hand experience, it would be even better.
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Old 18th October 2006, 05:06 PM   #13
SY is offline SY  United States
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Default ambisonics tech papers

Here's a short bibliography compiled by the late Michael Gerzon, a co-inventor.

http://members.tripod.com/martin_lee...nic/biblio.txt

edit: Basic equation of operation at wikipedia:

http://en.wikipedia.org/wiki/Ambisonics

Chemists will recognize the process as being the same one as mixing atomic orbitals, e.g., hybridization.
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Old 18th October 2006, 05:24 PM   #14
soongsc is offline soongsc  Taiwan
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Actually I found this site that probably provides more information.
http://audiolab.uwaterloo.ca/~jeffb/thesis/thesis.html
I think I'll sudy it a bit.

This makes me remember I was asked to quize a job applicant with a Masters degree in controls, I looked at his thesis and asked a simple question, "Why do you assume the sensor to be a constant?" His answer was "Because that's what they do in the books." That was the last of it. A simple answer would be that it can assumed to be constant within the well within the sensor performance bandwidth.

So lets see what we really understand from this thesis.
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Old 20th October 2006, 11:08 AM   #15
heater is offline heater  Finland
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Well I was thinking, if I'm going to do this at all it has to have 3-d capability, boring old 2-d is done to death isn't it? Now eight speakers seems to be enough to have to deal with. But an eight speaker cube as here http://www.york.ac.uk/inst/mustech/3...o/bdecoder.htm will never be a good fit in my home. Four speakers up is OK but four speakers down would have to fight with my sofa, tables, etc especially in the room corners.

Then the idea, why not tip the cube up on on of it's edges by 45 degrees?. So we have front left and right, back left and right. Then we have up-left and up-right near the ceiling. Then we have down-left and down-right in some available spaces near the floor, which can be easily kicked out of the way when not in use.

The magic of this is that there is a normal "front pair" for stereo (all be it with 90 deg between instead of 60 but they can be slid around a bit. Then a normal square rig for 2-d ambisonic and a 3-d rig with not to much junk on the floor.

So now, how to tweak the decoder parameters?
Hmmm well the wikipedia ambisonics page has the 3-d decoder equation. In to that I plug the angle of elevation of my up and down speakers, which if my rusty maths is correct would be inverse cos (1 / (root 3)) or about 54.7 degrees. Negative for down of course.

Any coments on this idea?

soonqsc:

Here is someone who doesn't want to just accept what the books say about ambisonics:
http://www.speech.kth.se/publication...inCarlsson.pdf
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Old 20th November 2006, 10:45 PM   #16
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There might be more material out there than is apparent; a number of people added a Calrec soundfield mic to their multitrack recording, and discovered that it didn't integrate any too well into the "improved stereo" multimic environment (try and record it as it ought to have sounded, but due to local acoustics,, dynamics between musicians, or the laws of physics, it didn't.) These "purist"track couldn't be released, as there was no accepted physical support to sell them on; and they still couldn't , because there still isn't (try and convince people they want a music/video room set up with 5.1 for video and those audio recordings specifically prepared in that format, and a second system with, at most two loudspeakers in common (and, even in that case, with the listening image rotated)
I basically live, work and occasionally sleep in a 5.1 studio, and though it's obvious that the standard was developed for picture support (there's a great big perforated screen in front of me) and is non-optimal for music reproduction (even ignoring the people who use the 5.1 just as stereo was used in the early sixties; effects for effects sake, movements, musicians all around you, I suppose it was predictable) but even so the difference when the music is flattened into stereo is every bit as impressive as the reduction of stereo to mono.
In the various surround sound forums I attend, it's generally accepted that present 6.1 and 7.1 systems aren't the be all and end all, and propositions of 10.2 (and even one Japanese gentleman proposing a 22.2 which could be matrixed down into practically any other standard - don't even ask what it would be recorded onto), in particular for eliminating the sweet spot (like waveform resythesis inside out)
But, while recommending clients to archive material in surround, I can't do as much for release; Most DVD players expect ac3, and the majority are connected to TV sets (neither a guarantee of quality) and, when they do run into a receiver, it's connected to loudspeakers the size of cigarette packets, that you woldn't accept in your car.
So, if there were a market for ambiosonic recordings, I'm sure the industry could be persuaded to release some of those old tapes (nothing they like better than selling something they already own and which will cos a minimum to remaster) but I can see no way of generating the market.
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Old 23rd November 2006, 09:45 PM   #17
Geoff H is offline Geoff H  Australia
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I find this quite a fascinating subject and past-time. My first venture into it was with 2 additional speakers connected in series, out of phase, with a w/w 50 ohm pot to adjust level. The whole lot connected to the + output of left and right.

It can add a true 2 dimensional effect, ie l-r and f-r. (There is no 3rd dimension unless you go up and down)

4ch vinyl with out 4 chan decoders sounded good, due to the fact they were recorded with 4 ch in mind. ie a good a-b mix, not ping pong.

Another scheme I have tried was an analogue decoder, where by difference signals are created, then mixed with left and right information. This allowed for greater control. This setup was used in the days when I was doing the sound for teen discos.

In a large area, this could provide an "on stage" atmosphere.

In a typical listening room, it will provide a good spatial effect, but not true ambience, I think that requires a time delay, or very mild reverb.

I find a lot of modern recordings are too discreet between the channels, and need a blend between left and right.

I haven't tried it yet, however, an extra speaker connected at the junction of the 2 rear speakers in the first example returning to ground or common will privide front centre. NB Don't try on bridged amps!

I have it on good authority that when Allan Parsons engineered "Dark Side of The Moon" he did so with 4 chan in mind, but with several standards for quad at the time, it was released as stereo.

The first track on "the other side of life" (Moody Blues) is also interesting, even if a bit "eighties"

I think one of the big issues with quad, is TWF. It's (was) hard enough to get decent front speakers into the lounge, let alone 2 at the rear or sides, and one in the centre.
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Old 24th November 2006, 04:33 AM   #18
el`Ol is offline el`Ol  Germany
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I find this is a link that should stand here:
http://www.ambiophonics.org
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