For as long as ambisonics has been around, there were also ideas of
active decoding. Even "infinite order decoding", actively. There's been
Harpex for two specular sources, derived from the theory leading upto
Dolby Pro, and then there's been DirAC, which additionally tries to
separate the reverberant field from the specular sources, which it then
at "infinite order" renders onto a rig via VBAP. So it's nice in all and
might work, but I'd say this work is not too principled or
generalizable.
I mean, none of this theory or technique actually seems to take the
ambisonic framework seriously. For example, none of it generalizes to
arbitrary order, or works with the harmonical functions. None of it
really works with spherical harmonics as HOA of does. For some reason
this kind of analysis leaves me...lacking.
So tell me, researchers, professors on-list, and your post-docs, might
you maybe delve into a couple of my amateur ideas and questions?
1) Express any active decoding solution in an infinite series of
spherical harmonics, utilizing only them. Becaause this kind of solution
would necessarily solve the active solution problem for any distribution
of sources, instead of just one, two, or in periphony even, four.
2) The mixed order problem. Years back I thought it'd be optimal to just
sum first and higher order order ambisonic signal sets together, and
decode them en masse, using a single decoder.
I was wrong: the optimal decoding for first and second order sets is
different. So, since people obviously mix first and higher order signal
sets, the optimal decoder needs to separate the contribution of each
successive order from each other, in order to optimally decode them. All
of the orders, overlapping slightly, to a degree.
This all can be systematically implemented via some variant of
non-negative matrix factorization, or a couple of related methods. I
believe.
Please try it out, or make someone try out.
--
Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front
+358-40-3751464, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2
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