A student, Mike (?) Evans, of colleagues of mine from the Department of Electronics at York did some work on a spherical harmonic representation of HRTF's back in the 1990's. I haven't got the paper handy but I seem to remember he ended up concluding you'd need something like 15'th order to get the errors low enough, but quite what his criteria were I don't recall. See "Evans, M. J., Angus, J. A. S., and Tew, A. I., (1998) "Analyzing Head-Related Transfer Function Measurements Using Surface Spherical Harmonics", Journal of the.Acoustical Society of .America., vol. 104, no. 4, 1998, pp. 2400-2411"
Dave On 26 January 2016 at 23:23, Politis Archontis <archontis.poli...@aalto.fi> wrote: > Hi Fons, > > I think I see your point, but I still believe they are equivalent in any > case? > In the end by having a lower-order sound field recording (eg B-format), > than the expansion order of the HRTFs at some frequency, the spatial > product is going to be limited by the sound-field order. If there is a > decoding stage in the middle, again a fully directional sound will be > spread to multiple speakers with an amplitude distribution determined by > the order of the decoder, and will be convolved with multiple HRTFs from > the respective virtual directions, essentially limiting the spatial > resolution of the HRTFs in the same way and to the same order. Are you > referring to any other effects of going through the virtual loudspeaker > case that would affect that? > > I see though the point of Jorn and Joseph’s of using dual-band (or any > other more perceptually-tuned) decoder. But i think that can be done also > in the spherical harmonic domain with no need for virtual decoding, as it > would be essentially a weighting of the components of each order (or a > convolution/ smoothing over the sphere). > > Regards, > Archontis > > > > On 27 Jan 2016, at 00:27, Fons Adriaensen <f...@linuxaudio.org> wrote: > > > > On Tue, Jan 26, 2016 at 10:05:07PM +0000, Politis Archontis wrote: > > > >> yes that is correct. I think however that the virtual loudspeaker > >> stage is unnecessary. It is equivalent if you expand the left and > >> right HRTFs into spherical harmonics ... > > > > True, but the problem with this is that it requires quite high > > order at HF (which is where all the binaural magic happens). > > > > But then you could say that any small set of virtual speakers > > would be inaccurate as well as it can't capture the high order > > dependency of the HRIR. This is true of course. The only reason > > why it works is that it relies on amplitude or ambisonic panning > > between the virtual speakers, just as reproduction via real > > speakers does. > > > > 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 > > Sursound@music.vt.edu > > https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, > edit account or options, view archives and so on. > > _______________________________________________ > Sursound mailing list > Sursound@music.vt.edu > https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, > edit account or options, view archives and so on. > -- As of 1st October 2012, I have retired from the University. These are my own views and may or may not be shared by the University Dave Malham Honorary Fellow, Department of Music The University of York York YO10 5DD UK 'Ambisonics - Component Imaging for Audio' -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20160127/4b3c798b/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, edit account or options, view archives and so on.
