[linux-audio-user] anti-compressing?

[Martin McCormick]

	What you are describing is the process of companding as in
COM-pressing and EX-panding.  It is certainly possible and is done in
lots of applications such as Dol bey sound systems of various types and
in communications systems.  It is a neat way of faking out the ear in
to thinking there is less noise on the system than there really is,
assuming one doesn't have too much noise.

	In order to properly expand the sound, however, one has to
know the characteristics of the level compressor such as the attack
and release times.  What you are doing is a mirror image of what the
compressor did.

	If you know that information, then you should be able to
restore dynamic range to the original recording.

	Sometimes, this technique backfires and you can get some
effects that are worse than nothing at all.  If the input level to the
expander is wrong, it will not track the compression and may cause a
booming effect to speech or music that wasn't originally there.

	If there is a lot of noise on the channel that wasn't on the
input signal, the noise will appear to puff or pump along with the
audio.  

	If one gets the level compression ratio and or the attack and
release times wrong, there is a whole boatload of weird effects that
can happen.  Your mileage will definitely vary.

Martin McCormick WB5AGZ  Stillwater, OK 
OSU Information Technology Division Network Operations Group

Andrew Gaydenko writes:
>Few days ago there was discussion in the list about mastering-CD/compressing/
>limiting/gain-upping and so on. I have strange feeling from the discussion.