I look forward to hearing that Fons - if you ever need a beta tester let me know
On 12 December 2012 22:25, Fons Adriaensen <[email protected]> wrote: > On Wed, Dec 12, 2012 at 07:20:31PM +0100, Natasha Barrett wrote: > > > 1. Proximity illusions on WFS at IRCAM: all four sides WFS arrays > > (BTW flat along the walls), sounds appear beside 'you', but then > > 'you' have to be in the right place. Kind of like one sweet spot > > for each sound point (and of course you have to be on the correct > > side of the traveling wavefront). Therefore there are mixing and > > composition tactics to get the best out of WFS proximity illusion. > > It sounds super, but as all spatialisation is in real-time you loose > > the advantage of HOA's encoding-decoding separation. > > The 'having to be in the right place' or at least the right side, is > probably unavoidable, whatever the system used. Focussing, no matter > how it's done, does not create a source. > > > 2. Proximity illusions on HOA at IRCAM: I worked with 7th order 3D > > over 75 loudspeakers and 12th order 2D over 25 loudspeakers. HOA > > alone will not, and is not supposed to, make *focused* sounds inside > > the array. HOWEVER, with the orders I worked with there are tricks to > > with sound motion, mixing, contrast, sound sources etc that gives the > > illusion of 'something' inside the array. But remember that this is > > to do with artistic use of the sound rather than embedded in the > > technology itself. And of course these high orders gave an enormous > > sweet spot / stable listening area! Completely different sound to WFS > > and it was great to use HOA and WFS at the same time! In fact quite > > depressing to return to my own lower order composition studio. > > > > I also made practical tests with implementations of published NFC-HOA > > theory (near-field compensated HOA). There is definitely something > > interesting perceptually - a 'kind of' focused source inside the array > > effect, not as spooky clear as WFS, but heard for the complete audience. > > With NFC the bass boost is still an issue even with compensation filters > > that end up removing the NFC effect (and so the technology still has some > > way to go). > > Indeed. HOA can actually produce focussed sources just as WFS can, but in > practice it is not an easy thing to do. > > The theory you'll find in Moreau's PhD thesis, dated 2006. > > A practical implementation is quite another issue. > > Let's trace the complete processing chain: > > 1. Mono source signal > > A. AMB panner with near field encoding of distance (optionally > compensated for the size of the reproduction array). > > 2. HOA 'B-format' signal > > B. AMB decoder > > 3. Speaker signals > > C. Speakers > > 4. Reconstructed sound field. > > (where 1,2,3,4 are 'signals' and A,B,C are 'processes' that convert > signals into some other form) > > The problem is that for focussed sources (2) and (3) will have very high > gain > resp. levels at low and mid frequencies, essentially the response rises by > 6 dB > per octave down per order. So for example a 10th order AMB signal for a > focussed > source will have components that rise in gain by 60 dB per octave as > frequency > goes down. Compensating for the reproduction array size in (A) instead of > doing > this in (B) mitigates the problem, but does not remove it. > > In practice that means that for focussed sources the speaker signals will > be at > extremely high levels, half of them in antiphase w.r.t to the rest, and > most of > the acoustic signals produced that way will cancel out in the > reconstructed field. > > That cancelling out means that most of the energy produced by the speakers > is > actually useless. To avoid this problem the frequency range of the higher > order > AMB signals (2) must be limited at the low end. And that must be done in a > way > that preserves their relative phase relationships. While the theoretical > near > field encoding filters are quite simple, adding the required high-pass > component > complicates them by some orders of magnitude, in particular if such > filters have > to be variable in real time as you would expect from a 'panner with > distance'. > > As shown by Moreau, such filters would actually limit the otherwise extreme > gains/levels to less than +6 dB, quite harmless in practice, while fully > preserving the focussing effect. Most of it is actually the result of the > _phase_ response of the filters, and not of the gain. > > I'm so far not aware of any existing implementation that actually achieves > this, except 'research' code for a fixed encoded distance and reproduction > array size. > > Some people (including me) are working on this, so maybe some day we'll > have > something that can be used for actual production work. > > 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 > -- 07580951119 augustine.leudar.com -------------- next part -------------- An HTML attachment was scrubbed... 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