On Wed, 2007-03-14 at 11:10 +0100, Joern Nettingsmeier wrote: > 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.
There's a supercollider implementation in the joshugens packages (UHJ.sc). It is meant to be played in stereo (ie: you "sorta" decode ambisonics b format to stereo). It's here, you can download the source from svn: http://sourceforge.net/projects/sc3-plugins/ -- Fernando