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

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
Received on Wed Mar 14 12:15:06 2007