On Thu, Oct 11, 2012 at 11:23:11AM +0200, Fabio Kaiser wrote: > So that means, for sound source directions in the near of the > horizon, speakers below the horizon also contribute and if I > leave them out I am missing something and get a false localization!?
Yes. Typically everything will move up. > So, Ambisonics in the end is also just creating phantom sources, > just using a little fancier approach!? What do you mean by 'constant > bandwidth'? Do you mean spatial bandwidth dependent on the order? Yes and no :-) At LF it reconstruct the field that would be created by a real source - there's no difference. It's a matter of terminology if you call that a 'phantom' source or not. For mid and higher F, the real field is not reconstructed, only some aspects of it that matter. At higher orders, what AMB does in this frequency range is not so different from VBAP, except that the directions corresponding to the actual speakers will not be reproduced by just one of those speakers, but get the same spatial lowpass filtering as any other. 'Constant bandwidth' is the name used to refer to a class of high quality interpolation or resampling algorithms. They are equivalent to applying a near 'brickwall' lowpass filter (with the cutoff frequency just below half the sample rate) to compute the values between the samples. The delay of the filter is modified in function of the position of the output sample w.r.t. the input samples, but the magnitude response is always the same, hence 'constant bandwidth'. So even if the output sample coincides exactly with one of the input samples it will be filtered. Compare this to 'geometric' interpolation (linear, cubic, etc.) where this is not the case. > Still, practically I cannot place source below the horizon, I even have > to shift the horizontal ring in elevation by somewhat 15°. So, is my > approach still valid for the layout and I just have to take care of > that in the decoder design? What decoding approach would you recommend? In practice, to preserve the AMB nature of the decoding you need the first 'below the horizon' ring also for an hemisphere. For the 3rd order layout I described earlier, that means you need the ring of 6 at -45 degress elevation. At higher orders you would have more rings, the first one would be closer to the horizon, and you could leave out the others. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
