Yes it seems I had a ‘brain fart’. The source file is Ambisonic and the pre-processed file is for an Ambiophonic ‘PanAmbio’ arrangement of speakers.

The speaker geometry I am using for this is a narrow rectangle, 30cm. across (between speaker centres) and about 2.5 metres between the front and rear pair.

Additional information to Raph’s http://www.ambiophonics.org/ can be found here:
http://wwwnew.isvr.soton.ac.uk/FDAG/vap/html/sd.html
http://ambisonic.info/info/ricardo/ambiophonics.html
http://www.filmaker.com/papers.htm
http://www.princeton.edu/3D3A/

My present filters are more optimised for intensity stereo than the pure X-talk cancelling filters described, which are aimed more towards recordings using some sort of microphone which includes a real, or simulated head shadow effect, and interaural delay, This should make them well suited to Ambisonic recordings. How it it is that it seems to reproduce height is a bit of a mystery, but I have some crackpot theories to work on..

David.

Do you mean ‘ambisonic’ instead of ‘ambiophonic’ in the second paragraph above … I’m confused (I’m not familiar with ambiophonics at all).

I can take the blame for both soundofspace.com and the UA format … both are my work. I know it is all under-documented. I’m a one-man-band and open-source support keeps failing me.

I think you are right about the difference between ambisonically recorded vs encoded sounds. Whilst the maths for encoding point sources of sound ambisonically appears quite simple, actually encoding the behaviour of sound in space is very complex (and requires pretty good knowledge of psychoacoustics).

You are right that I haven’t tried it….. but …. yes OK … I will try it on the iPhone app.

It took me most of a day searching the mass of Ambiophonic ‘stuff’, and trying various audio editors, to discover in the small print the simple fact that renaming a file from .amb to ,wav enables it to be read into AudioMulch and that c:/wvunpack.exe y:/jhroy_rain-over-the-tent.ua will make the four channel wav file y:/jhroy_rain-over-the-tent.wav

It does not seem that anyone has tried, or is likely to try, an alternative way of decoding Ambiophonic files

http://electro-music.com/forum/topic-49067.html
“I have recently made an Ambisonic to Pan-Ambiophonic-thingy decoder. I hope you can try this Pre-processed files as you are probably one of few people set up to do so.
Stereo-dipole – front channel 1.2 , rear channel.5,6, Channel 3.4 empty.
Source file from here:
http://soundofspace.com/ambisonic_files/58
My dual Ambiophonic file here:
http://www.megaupload.com/?d=7MX2W3FR
AmbiFusion-DW-jhroy_hot-air-balloons.aac
You should hear 3D ie. including height. ”

Ambisonic recordings are just fine, but the idea that the maths supports the idea that one can recreate the soundfield, at even for a small blob of space, by making standing waves and interference patterns , is either wishful thinking, or somewhat dishonest. The process is irreversible, IMO.

David.

I think all spatialisation technologies will be knocked about a lot by the acoustic of the performance room … especially if it is reverberant. You probably know more about the subtleties of the various technologies than I do … but in this instance it turned out that only a semi-circle of speakers was used (limited to the stage). Ambisonics would not have fared well here … perhaps that is the principle advantage of VBAP … sounds can be localised within restricted layouts.

The impression that the localisation was stronger than it would have been if done ambisonically was subjective… but I think I can explain it. Given the limited number of speakers (I think 4) I was surprised at how focused the sound source was. If 4 speakers had been used ambisonically (covering a 360 area … instead of a 180 deg area) the focus of the sound source would have been less. In this sense I guess you could say that I was projecting my expectation of the focus of sound location on what I knew was possible (ambisonically) with 4 speakers. To get that level of sound source focus on a 180 deg stage, with 4 speakers, in a reverberant environment, was impressive.

Of course, the Ambisonic decoder is a big barrier currently, which is why Ambisonic audio should be presented and distributed as speaker feeds…..the audience then need never know that it’s Ambisonics or VBAP or Pro-tools 5.1 panner, or Reaper’s or whatever. In they end they don’t, and shouldn’t care (generally). We’d never ask a comsumer to install pro-tools to listen to a mix made with their panner, we shouldn’t ask people to install anything to listen to Ambisonics either…..Ambisonics should be (and is in some circles!) a production format only at the moment.

cheers

Bruce