On 12/02/25 16:35, Doug Lee wrote:
On Tue, Feb 11, 2025 at 07:49:38PM +0100, SoX NG wrote:
so I've replaced it with a different example: Dolby A compression and decompression,
which is probably also more useful as I think more people still have tape recorders than
need to compand for FM radio.
https://codeberg.org/sox_ng/sox_ng/issues/408 - The "mcompand" example doesn't work
I do get an error on the final element of the decompress mcompand though:
".1,.1 4:-41,-56,-21,-36,-23,-26,-14,-17,-9,-9"
does not increase monotonically.
Ah, thanks for reporting that.
Dolby does it with 3-20kHz and 9-20kHz companders in parallel,
which mcompand can't do in one invocation.
It was my attempt to make 5dB more to the difference ramped down
to 0db in four steps without using decimals and I got it wrong.
Now it adds from 4dB down to 0dB in 4 steps. Can't stand decimals,
can't hear 1dB difference, in fact can't hear above 9kHz any more, sigh.
# Dolby A compressor
sox_ng in.au dolbyA.au mcompand \
".1,.1 4:-56,-46,-36,-26,-26,-20,-17,-15,-9,-9" 80 \
".1,.1 4:-56,-46,-36,-26,-26,-20,-17,-15,-9,-9" 3k \
".1,.1 4:-56,-46,-36,-26,-26,-20,-17,-15,-9,-9" 9k \
".1,.1 4:-56,-42,-36,-23,-26,-18,-17,-14,-9,-9"
# Dolby A decompressor
sox_ng dolbyA.au out.au mcompand \
".1,.1 4:-46,-56,-26,-36,-20,-26,-15,-17,-9,-9" 80 \
".1,.1 4:-46,-56,-26,-36,-20,-26,-15,-17,-9,-9" 3k \
".1,.1 4:-46,-56,-26,-36,-20,-26,-15,-17,-9,-9" 9k \
".1,.1 4:-42,-56,-23,-36,-18,-26,-14,-17,-9,-9"
Not like I actually tried running it after the mod or anything.
Just too confident.
Thanks again
M
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