On Wed, Feb 29, 2012 at 5:19 PM, Sampo Syreeni <de...@iki.fi> wrote: > Personally what I find a bit worrisome is that this sort of optimization > retains the blackbox leanings of machine learning as a general discipline. > None of the ambisonic specific, closed form optimization literature, or the > derived specifics of the base optimization problem, are being utilized. > Instead the two (sometimes simultaneous, sometimes even not that) Gerzonian > equations are being fed into one or another optimization framework, with no > regard to what happens then, and without feeding in all of the age-old > mathematical-physical knowhow of how those systems of equations behave. Like > for instance psychoacoustical sensitivity estimates from the BBC era.
Indeed. But in 100 lines of fairly simple code or so — you have something that produces usable matrixes. > I'm also a little bit of a skeptic towards the > stuff. At least as far as the math I know and love suggests I should be. It's not magic, for sure— but the problems we solve here are small (few dimensions), and relatively smooth (except where they aren't as you note there are singularities)... and you can usually afford throw billions of cycles at them. While we weren't looking computers got _fast_. > I don't think going with the easy route and just using blackbox optimizers > does the job best, here. Absolutely not. But it gets you something right away. Theorizing about the best psychoacoustic criteria doesn't— and it seems like most of the people who have invested a lot of time thinking about this problem go the closed source opaque route thus failing to advance the public science... even many people who do proper research in this space only output papers, which while informative often don't do much to advance the _practice_ of surround listening (perhaps the closed source folks implement their techniques). > That isn't being done now. Even to accelerate convergence, or to give a > global, smooth starting point for the optimization procedure(s), or to > regularize the eventual outcome. Why not? Are we really that lazy (well I > am, but are the researchers in the feel as lazy as me as well?) Dunno about you, but I'm pretty darn lazy! >> https://people.xiph.org/~greg/ambisonics/ambi_opt.c > > Under xiph.org? Ooh! Please, more of that. And then more reseach plus > application in how to optimally code/decode even first order using Vorbis > (or some derivative?). Back in 2007 I created a special Vorbis mode for coupled first order b-format. I thought I posted about it here, but I can't find the message with a quick search. I don't have a surround reproduction rig .... so I was unable to listen to it, and I just wanted feedback about how it sounded. IIRC I didn't get any feedback. ::shrugs:: I doubt I still have the modes or files anymore. My general belief is that (with carefully constructed formats and encoders) fairly modest bitrate perceptually compressed audio can sound excellent— and if we want to increase quality further with more bits what we should be doing is going to (increasingly high fidelity) surround before decreasing lossyness. Unfortunately, high quality surround content and playback rigs are still scarce. ... and the ITU/MPEG crowds approach to lossy surround coding appears to be excessively parametric— very few bits but its mostly only good for creating ping-pongy effects and motion sickness. (probably a catch 22 with the non-existence of good content and playback rigs, why make lossy codecs for acoustic holography when people are only doing quadrophonic-redux pingpongy stuff?) In any case, the lack of practical deployment of really surround systems has made surround coding stuff stay low on my priority list even though I care about it personally— work in that area, for me, has fairly little improve-the-world bang for the buck. _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
