On 12/02/25 20:56, Doug Lee wrote:
Off-list communication on this one welcome so we don't stray too far. :-)
Me, I tend to write off-list messages and then sent to the list by mistake.
Fortunately I seldom say anything too outrageous :-)
However, as long as it's relevant to anyone interested in precise low-level
audio processing...
On Wed, Feb 12, 2025 at 08:21:34PM +0100, Martin Guy wrote:
Do the flow diagrams work for you
On paper yes those can work if brailled right; but on a computer, at least I personally don't usually follow those.
Thanks, I'll keep that in mind.
I understand compand and mcompand fairly well but am not an expert at crafting effects for specific
> purposes with them.
For that I had to dig out Ray Dolby's original paper plus a few other
descriptions
and measure his hand-drawn graphs with a ruler to figure out the curves'
coordinates
but was happy when one followed by the other produced something that
sounded the same.
The --plot output was very similar to the original diagrams so it went
fairly well.
Dolby B and C instead have a single sliding frequency band, not
something I think SoX can do,
but they are worse cheap versions for consumer boxes.
A recent example where I did not succeed was a recording someone sent me where the
volume cut way down at a certain point.
The new "softvol" effect may help here. It's a simple volume multiplier that
immediately reduces the volume when a sample would have clipped and
optionally increases the volume continuously so that it doubles every N
seconds.
I use it all the time to blast the quartiere with nonstop music as it
makes the
audibility of the result independent of the original recording volume
and stuff in the quiet passages as audible as in the loud ones.
Since I start at volume *= 400 (!) the very start of each track is
always interesting.
There's an extreme example of it at work under http://martinwguy.net/test -
the long filename full of sox effect names.
However, I'm not sure you *can* restore something like what you describe
to its original dynamics because information has been lost.
I did, though, just write a small Python utility for scanning files via sound very fast
using a two-stage SoX pipe and 1-10ms tones on a 256-frequency range to represent bytes
Do you mean a single tone that blips at one of 256 frequencies according
to its value and
recognizing certain characteristic sequences? Interesting.
One of my passions is for log-frequency-axis spectrograms, which
translate sound from
the audio domain to the visual one - not a lot of use to you but maybe
for deaf people to
let them see speech and music - however there are inverse techniques to
turn a spectrogram
back into the original sound, or a best effort at it. Peter Zinovieff's
tried this in the 1960s
and in one of his notebooks describes scanning a picture of a flower and
converting it into
sound as a particularly fascinating experiment. My own efforts in this
direction are documented
at https://wikidelia.net/wiki/Spectrograms#Inverse_spectrograms
That suggests adding JPG and PNG as input and output formats to SoX
as synonyms for spectrograms without axes, presumably with the lower and
upper frequencies and the pixel-columns-per-second and dynamic range
in image comments or as format parameters.
One thing at a time though...
M
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