Aaron Heller wrote:
On Thu, Apr 21, 2016 at 12:14 AM, Trond Lossius <trond.loss...@bek.no>
wrote:
On 20 Apr 2016, at 21:16, Marc Lavallee <m...@hacklava.net> wrote:
I wonder why using uncompressed PCM instead of compressed AAC...
Is there a risk of compressed audio altering the phase between the
channels, affecting the spatial image?
Marc and I looked at this informally when he was developing ambisonic.xyz.
We took panned first-order B-format (e.g., AJH-eight-positions.amb),
though an encode/decode cycle with candidate codecs, and then looked at the
spatial spreading of energy with a simple parametric decoder. No listening
tests, just visual comparison of plots of spatial energy.
We found very little spreading with low-complexity AAC, but a fair amount
with HE-AAC.
Aaron Heller (hel...@ai.sri.com)
Menlo Park, CA US
HE-AAC: You could not use certain "tools", such as SBR and (parametric)
joint stereo.
Otherwise, HE-AAC (two versions...) is still significantly more
efficient than LC-AAC. (TNS is < one > of the new tools somebody could
use for Ambisonic channel compression)
http://www.img.lx.it.pt/~fp/cav/Additional_material/SPM_Standards_HE_AAC_Final.pdf
(introduction)
Best,
Stefan
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