hi and thanks for your posts! I made some progress thanks. I took a look at the abcdefg 3D-Mixer from IOhannes (great stuff), which was a little easier for me to understand: http://puredata.info/Members/zmoelnig/abcdefg
and it has a documentation(!): http://iem.at/~zmoelnig/publications/abcde/
I think this is much more fun than computing b-format files, because evrything can be done in realtime. I still have to check out which output channel gets asigned to what speaker. I think this must correspond to the order of the angles.mtx file, where the positions of the speakers are written, but I'm getting some funny sound positions. Most probably some mystake of mine. It was rather easy to set everything up until now. Just a few more questions.
- Is the cubemixer better (dispite of the gui) than the abcdefg-3Dmixer?
It looks more fancy, but is there some important feature I'm missing?
- IOhannes wrote: "you will also have to reduce the ambisonics order to 1st
order only (which is b-format) since the number of loudspeakers must be = the number of ambisonic channels which are (n+1)² (with n being the order)" How do I reduce the ambisonic order in the abcdefg? Is this necesary for the abcdfg? Is it just about reducing the number of output channels from the encoder, in the abcdefg.conf file?
- I've read in the documentation, that for sounds to come from the bottom,
one has to put loudspeakers on the floor. Are the elevation angles for the position of the speakers in the angles.mtx file negative? Like 0 -90?
The hdsp multiface seems to work fine with oss emulation. When I tried alsa, it distorted the sound from an osc~ in a peculiar way.
cheers, rodrigo
Roman Haefeli wrote:
hi rodrigo
afaik, the number of speakers for an ambisonic installation doesn't matter, since you first compute an ambisonic sound in the B-Format, which has always 4 channels, iirc. once you have the b-format computed,
yawn...who still uses the b-format nowadays? b-format is just a very small subset of ambisonics (otoh, when you are stick to 8 channels b-format will be the best you get...)
you can use it for several configurations of loudspeakers, but you'll have to measure the position of each loudspeaker and then compute the signal for each speaker accordingly.
i don't know the cubemixer of iem, but the website (http://iem.at/projekte/acoustic/awt/abcde/project_view) says:
"Dabei wird nach dem ambisonic-Prinzip eine mehrkanalige lautsprecherunabhängige Repräsentation eines periphonen Schallfeldes generiert (Encodierung), und diese anschlieÃend über ein bestimmtes Lautsprechersetting (Hemisphere) wiedergegeben (Decodierung)."
for me it sounds that you can use the cubemixer to compute ambisoncics b-format (encoding). so you could do the decoding afterwards for your special configuration, which has 8 instead of 16 speakers.
yes, that is what ambisonics is all about.
basically you should have a look at the decoder~ on the DSP-side. iirc, somewhere it should read in a matrix (or something similar) of loudspeaker positions: adapt that to your needs.
additionally you will also have to reduce the ambisonics order to 1st order only (which is b-format) since the number of loudspeakers must be
= the number of ambisonic channels which are (n+1)² (with n being the
order)
hopefully i'll have more time to answer your question better next week.
mfg.asd.r IOhannes