Re: speaker layouts You might be interested in some work I did on choosing the right positions for loudspeakers to minimize the spatial aliasing (actually spatial imaging is a better name in the case of rendering, keeping with the DSP terminology). With these designs you can use some sort of least-squares + regularization technique for decoding without too much trouble. Spherical sampling above 1st order is a tricky problem and very interesting that seemingly good layouts (such as Fliege or minimum energy designs) are sometimes really poorly conditioned for spherical harmonic analysis/synthesis.
I can provide MATLAB code (that requires the optimization toolbox) to anyone interested. The code also allows you to bias the array towards better horizontal reproduction (say for a 1st order 3D, 3rd order 2D design). The paper is: J. Atkins, “Optimal spatial sampling for spherical loudspeaker arrays,” Acoustics Speech and Signal Processing (ICASSP), 2010 IEEE International Conference on, pp. 97 – 100, 2010. link: http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5496174&tag=1 Josh 2011/5/2 Jörn Nettingsmeier <[email protected]>: > On 05/02/2011 11:50 AM, Marc Lavallée wrote: >> Mon, 02 May 2011 06:59:40 +0200, >> Jörn Nettingsmeier <[email protected]> wrote : >> >>> not native, but here's a very simple one that has been shoehorned >>> into a third-order workstation: >>> http://cec.concordia.ca/econtact/11_3/nettingsmeier_ambisonics.html >> >> I'd like to understand the "Versatile (and Quite Luxurious) Speaker >> Setup" part of your article, and how it relates to your recommendation >> on the number of speakers: > > first of all, this example was picked more or less out of thin air in > order to show that there are really no limits on the type of layout, as > long as it's more or less regular. it's no standard, and i must confess > i have never mixed on exactly this setup (although i created a similar > setup once, for a temporary installation). > >>> in production, use HOA. in reproduction, use as many speakers >>> as you can afford, up to a limit determined by the order of the >>> source material: >>> 1st OA: no more than six >>> 2nd OA: six or eight >>> 3rd OA: eight, twelve if necessary >>> >>> it's now an established fact that too many speakers degrade >>> the result for any given order. >> >> Is your "versatile" setup appropriate for 1st, 2nd and 3rd OA? > > if you can afford eight speakers on the horizontal plane, you get some > kind of native 5.1 that is not totally wrong, certainly no worse than > what you find in most homes (if you find 5.1 at all). > and you can do native quad, you can do first order over four speakers, > and first, second and third over all eight. lots of opportunities for > a/b comparison. > > when i mix, i always run several decoders in parallel, with subsets of > my maximum setup, to see how the mix degrades. so i work in third order > (if i can - my home setup only does 2nd), but i will frequently fall > back to first order on all speakers or just a subset, or even UHJ stereo > - my goal is to find a middle ground that delivers good UHJ stereo to my > customer and also retains ambisonic goodness for the future. > > so yes, i do care how it sounds in first order. but it's like a mono > compatibility check, not like it's my primary target. > > almost all recordings i do, i think in surround and fold down to stereo, > even if it is clear that the customer won't ever care for surround at > all. only in cases of emergency will i use stereo-specific tweaks. > >> Does the elevated hexagon work with FOA, or is it only for HOA? >> Is the octagon good for FOA, even if you don't seem to recommend it? >> Finally: is it a good setup for domestic listening? > > this setup is very likely overdone for first-order. i haven't explored > first-order periphonic much, but i swear by the regular hexagon for > first-order horizontal (and it's also very nice for second order). > > in my experience, first-order horizontal over eight speakers is slightly > but noticeably worse in the sweet spot than six, so not recommended for > homes if you seldom if ever listen to third order material. > > for larger audiences, the game seems to be a bit different, although i > don't quite understand why. i find 1st order over eight speakers covers > a larger area more easily and uniformly than six, but the theory says it > shouldn't, because outside the sweet spot, rV reconstruction is mostly > not happening and everything relies on rE, which is degraded by using > more speakers than necessary... > > if i were to build a periphonic rig at home (which i might, when i have > the spare cash), it would be three on the floor, six at ear height, > three on the ceiling, i.e. a slanted dodecahedron. should be good for > second order periphonic, still small enough to be able to enjoy native > soundfield recordings without ruining the rE too much, and no compromise > for horizontal-only material. > > if you're not interested in sounds from below the equator (which means > you'll miss all those exciting footsteps and running water sounds), you > could try a hemisphere with eight and four and maybe an added zenith (or > just six and three), but then you need some spherical harmonic alphageek > to compute a decoder for you that doesn't pull upwards like crazy. > i'm trying to learn how to do it, but i'm only beginning to understand > the problem, nowhere near to getting it done myself. > > many people swear by stacked rings, and i can say that the one time i've > had the chance to work on three rings-of-eight, i was amazed to find no > noticeable phasing issues, even though the room was almost dead (rt60 of > 0.3s down to at least 150hz, the lovely SPIRAL rig in huddersfield). > stacked rings still feel a bit wasteful to me, and they have these holes > at the bottom and up top (where the SPIRAL has recently added a zenith > speaker), but the absence of phasing was quite striking. i have too > little experience with rings to conjecture a general rule from this, but > i'm looking forward to my next stacked ring setup... > > -- > Jörn Nettingsmeier > Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487 > > Meister für Veranstaltungstechnik (Bühne/Studio) > Tonmeister (VDT) > > http://stackingdwarves.net > _______________________________________________ > Sursound mailing list > [email protected] > https://mail.music.vt.edu/mailman/listinfo/sursound > -- Joshua Atkins Ph.D. Candidate Dept. Electrical Engineering Johns Hopkins University 3400 North Charles Street Baltimore, Maryland 21218 _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
