On 13/02/25 03:04, John Dyson via Sox-users wrote:
About the DolbyA thing...
All I could find was a mention of "about" 0.1s attack time, apparently
the same decay time,
12dB/octave shoulders to the filters (not an mcompand parameter at present;
I dunno what it uses, 6dB per octave seems to be usual)
measuring Ray's graphs in the paper with a ruler, and someone saying that
it gets up to 10dB difference most of the way (which corresponds exactly
to the linear lower section of Ray's graphs) and up to 15dB at 15kHz,
which I took to mean the combined result of the parallel 3kHz and 9kHz
filters,
forgot to include the 4db "knees" so that the curves are rounded instead
of having corners
and rounded the figures to no decimal places so that each line would fit
into 80 chars.
If you have more precise detail about what Dolby A should be, I would be
happy
to amend the example so that it's closer. I'll even include decimal
places ;-)
Adding a parameter to mcompand to specify the steepness of the filters'
shoulders
also seems necessary for this use case, if I can figure out how to do that.
(Also, the Q values for the band splitter are approx 0.42 for 8.8kHz,
0.45 for 2.7kHz
> and apprx 1 or 1.2 for somewhere around 75-80Hz??
Hmm. So filter shoulder steepness would need to be specifiable for each
frequency crossover point.
> Truly encoding/decoding DolbyA materials is a totally different world.
Yes. Emulating existing analog electronics is a totally different world.
Csound might be able to help;
it makes SoX look like a handcart, but then their application domains
are quite different.
It is probably very off topic for this mailing list...
Not if it affects needed changes (or, rather extensions) to SoX.
I need to know what people use it for and how it could be improved in
the light of that.
M
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