[opus] Antw: Re: Antw: [EXT] Opus merging streams

Sampo Syreeni decoy at iki.fi
Wed Apr 6 06:36:33 UTC 2022

On 2022-04-06, Ulrich Windl wrote:

> Incidentially I came across a Dolby Atmos demo that had about 118 
> channels wirh 24bit audio at 48kHz, all in one huge WAV file 
> yesterday.

Is that even a legitimate encoding?! What the fuck.

> When I tried to play that (in plain stereo) with audiacity, even my 
> fast computer (i7 at 4GHz) had dropouts. So I can imagine that 
> decoding a large number of channels and mixing those seems to be a bad 
> idea.

It is. Which is why my favourite ambisonics exists (sales pitch): it's a 
principled and nigh entropically speaking optimum way to fold down a 
static central soundfield down to a number of channels. Third order, so 
sixteen channels, seems to be upto the task for *any* central isotropic 
soundfield at all, and the system yields to static optimization.

I cannot for the life of me understand why Atmos exists. Except for 
patent patent law or something like that. If it was used to express a 
live gaming or augmented reality setup, with arbitrary auditory 
parallax, I could get the point. But that's not what Atmos or even Dolby 
AC-4 are about. They just encode a static scene -- in a way *much* more 
complicated and heavier on the processor than a "simple" third degree 
periphonic ambisonic HOA signal set would be, and in a manner not 
amenable to low resource optimizations in surround sound. The object 
based encoding simply seems stupid and superfluous.
Sampo Syreeni, aka decoy - decoy at iki.fi, http://decoy.iki.fi/front
+358-40-3751464, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2

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