On Tue, Jun 04, 2013 at 01:52:57AM +0300, Sampo Syreeni wrote: > On 2013-06-03, Fons Adriaensen wrote: > > >Note the sqrt(k) factor in eq.(4). This the 3dB/oct factor I > >mentioned before. It arises because in the derivation of the > >driving function vertical line sources are replaced by point > >sources, and NOT because the resulting line array of secondary > >sources behaves as a line source. > > True. But isn't that precise thing also happening within pantophony, > if not in WFS's cylindrical symmetry, but in ambisonic's toroidal > one, too?
No. > ... > ... > Or so I think. What am I missing? You're mixing up so many things in a single paragraph that it becomes impossible to decode what exactly what you are saying, and even more impossible to respond. Please stay focussed and follow a clear line of reasoning instead of pulling in something new every two lines. > >There is no similarity at this level between AMB and WFS, because > >even if the speaker arrays can be the same they are being driven > >in an entirely different way. The two systems do _not_ converge in > >the limit. > > In the 3D limit they do. So isn't that yet another reason to believe > what I'm saying is true? I mean, they'd pretty much *have* to > converge even here if it was only about amplitude by distance, when > the distance was set to the pantophonic array radius in the > ambisonic case, and as the same radius for the circular variant of > WFS. No? No they don't converge, and as long as you assume they do you will be deluding yourself and come to the wrong conclusions. Compare a WFS system and an AMB system using the same secondary sources, at an order compatible with the number of speakers. Both systems recreate the sound field up to some point. Since this can't be perfect there have to be trade-offs, and those are very different for WFS and AMB. * WFS recreates the field in almost the entire interior area, but only up to the aliasing frequency. * AMB recreates the field for the entire frequency range, but only in a limited area having a radius proportional to wavelength. So the _results_ are quite different. No look at the signals driving the secondary sources. If you calculate the WFS signals it turns out you need the 6dB (3D) or 3dB (2D) per octave filters. If you calculate the AMB signals no such filtering turns up. So the driving signals are very different as well. The difference, in simple words, is that WFS is using the line (or planar) array as a line (or planar) array (and that's why the normal to the line or surface turns up in the equations), while AMB does not do this. Imagine a circular array. For a single distant source, AMB will use only two or three speakers, those closest to the direction of the source (the contribution of the others will be *very* small at high order). WFS will use half of the circle, with a cos(angle_to_source) distrubution. Now show me how those two converge to the same... They simply don't. 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
