On 2010-11-04, f...@kokkinizita.net wrote:
Seems you are completely out of touch with the context of this thread.
That more than possible. But still, if you don't mind my asking, why be so harsh about it, all of a sudden?
There's nothing 'naïve' about in-phase. It may look as something fundamental to you but it isn't.
To me in-phase is one of the fundamental decoding cases because in Stanzial et al's energy propagation sense it minimizes the standing part of the field within the array wrt the propagating one. Or rather it comes close to that: without lots of extra symmetry I'm not willing to say this is the minimum, or even a local minimum, but I'm still willing to claim that it's within a bounded distance of the optimum in absolute complex magnitude integrated over the inside of the rig, where the distance should be able to be bounded above by one or another asymmetricity metric wrt the rig geometry.
My comment started with my age-old disagreement with Filippo about how free-field mic arrays interact with soundfields. Originally I was thoroughly certain that a sphere of mics in the free field could always capture the entire soundfield, if properly spaced and processed right. In the end, Filippo showed that I was wrong, on physical grounds: this is not possible using just a curtain of monophones, because the boundary conditions needed for the wave equation were not there in this case. After that I privately convinced myself that it couldn't really be done in theory even with directional microphones, eventhough arrays of directional microphones could still come increasingly close to what Philippo and the literature said was the primary condition: a boundary within the array.
Now, we all know from the ground up that mics and capture on the one hand, and speakers and playback on the other are very much dual within the ambisonic framework. If something goes amiss with one, it pretty much always goes amiss with the other as well, and for the same reasons. So, I've mulled for a long time over what might go wrong with a rig, analogously to that mic example Filippo gave me.
I am not sure whether this acute problem has anything to do with what I've been thinking about. As such, I presented a simple test to try it out: does the problem go away if the array diameter is sunk, while the directional aspects stay the same? That would suggest it has something to do with diameter above directionality. So would the possibility that the problem shifts to a different frequency band.
In particular, this kind of problem would manifest itself audibly with very regular, rotationally symmetric arrays, which pretty much nobody outside of this list has. If somebody else heard them, they would likely mistake them for room modes or somesuch.
So I think a mere question and a simple suggestion for a test is justified here.
-- Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front +358-50-5756111, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2 _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
