Hello, I wanted to find out more about square polar mapping, cause that whole stuff is a bit tricky - to me - and not so easy to understand. Searching the web did't get me any results, so I wonder what the background of square polar mapping is. Is it derived from some mathematical publications or just the result of a brilliant intuition of a Vorbis programmer ? ;) Thanks. Stoffke <p>--- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
On Friday, May 23, 2003, at 01:56 am, Stoffke wrote:> I wanted to find out more about square polar mapping, cause that whole > stuff is a bit tricky - to me - and not so easy to understand. > Searching the web did't get me any results, so I wonder what the > background > of square polar mapping is.I assume you've seen http://xiph.org/ogg/vorbis/doc/stereo.html ? It describes the transformation fairly well (for the 2d case, anyway).> Is it derived from some mathematical publications or just the result > of a brilliant > intuition of a Vorbis programmer ? ;)I always assumed this was something monty came up with independently. I suppose it's a bit like a polar version of the manhattan metric, but I've never seen a reference to it elsewhere. The whole point is just to avoid the trig functions. Hope that helps, -r --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
> I assume you've seen http://xiph.org/ogg/vorbis/doc/stereo.html ?Yes I've read the specs, but it's not quite easy for me to understand .> It describes the transformation fairly well (for the 2d case, anyway).Does that mean there're more than 2 dimensions possible in SPM ? <p>Let me recapitulate the things that I understood from the specs: The encoder separates the spatial audio information (how exactly is not said in the specs ) into a "point" and a "diffuse" component. These two components are than coded into a vector. The magnitude of the vector represents a "point image". A point image is a sound that can clearly be located somewhere in the stereo field. What if there are more than one "point images", for example two intruments, one clearly on the left and the other clearly on the right side ? The angle of the vector represents a "difuse image" - that seems to fill a larger area with a diffuse sound, like reverberation. The L/R channels can be restored by a simple algorithm, based on subtraction and addition of the magnitude and angle values. Bits are saved by allowing only a few discrete angle values But i think the whole SPM is discrete, right? It was said in the specs, that there are 121 possible vectors. Or was that just an example ? With the quantisation of the vector to only a few possible angle values, some "diffuse image" information are thrown away - at least the higher frequencies above 4 kHz. But this is little noticeable to the human ear. Hope I got it all right. Regards Stoffke <p>--- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.