[linux-audio-dev] 2-channel stereo compatible ambisonics...

[Joern Nettingsmeier]

Steve Harris wrote:
> 
> On 13 Mar 2007, at 09:15, Valent Turkovic wrote:
> 
>> Hi,
>> is it possible to record multi channel speech audio and down sample it
>> 2 stereo channels BUT with horizontal audio positioning of each audio
>> channel ie. like dolby surround effect.
> 
> Sure, but you might be disappointed by the results, Pro Logic is not 
> very sophisticated (eg. there's no separate rear left and right channel, 
> and the bandwidth is limited). Also the only free software 
> implementation that I know of is not state of the art, partly due to 
> patent problems, and partly due to lack of interest.
> 
> There's a LADSPA plugin: 
> http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html#id1401
> which does Pro Logic matrix encoding, you will need some other software 
> to mix your independent streams into LCR channels (you can do it by ear 
> with a 3+ variable send bus mixer), but once you have that you can feed 
> it to the plugin and get a pro logic compatible stream out.
> 
> PS ignore the documentation, it has been tested, and it does work, just 
> not brilliantly. You will get better results if you EQ the mics a bit to 
> cut the level of the highs and lows a bit, especially in the rear channel.
> 
> You would get much better results with an ambisonic stream, but I don't 
> /think/ you can make stereo-compatible ambisonic streams, and not many 
> people have ambisonic decoders. Other people on this list know a lot 
> more about ambisonics though.

i'm very new to ambisonics, so i may be wrong, but i think there are 
indeed stereo compatible first-order ambisonics streams. iirc, the 
format is called UHJ, and it matrixes WXY (lossily) into L/R (i.e. no 
height information).

i've changed the subject to bait fons :-D
if we're lucky he knows an implementation of 2-channel UHJ.

i found this article: http://www.ambisonic.net/ambi_AM91.html
but it does not give details as to how the matrix encoding is accomplished.


regards,

jörn