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Topic: Inverting Dynamics Compressor (Read 3586 times) previous topic - next topic
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Inverting Dynamics Compressor

While ReplayGain may solve the problem of overcompressed tracks coming out too loud, it doesn't solve the problem that those tracks are still ripped off all their dynamics.

My question is: is it possible to invert a dynamics compressor? I.e. make a dynamics expander.

A problem would be that you don't know the exact settings, however, what if you would just assume 'industry standard' compression and figure out the amount by looking at the ReplayGain output?

Possible? Usable?

--
GCP

Inverting Dynamics Compressor

Reply #1 –
It seems possible to me in theory as long as you know exactly the kind of compression, the ratio, the threshold, the attack and the release.

In practice I don't think it's possible. Major problems would be multiband compression (you need to know the above parameters for each frequency band), and multitrack compression (maybe each track was compressed differently before being mixed together).

Inverting Dynamics Compressor

Reply #2 –
Well, there really is no "industry standard" compression settings, it's completely on a case by case basis, and up to the desires of the producer.

Overcompressed crap, unfortunately will remain overcompressed crap.  You could go through yourself with an expander on a song by song basis and try to play mastering engineer on the stuff you really like, but again, you might make some difference, but once the damage is don, it's done.  Kind like trying to make a 64Kbps mp3 sound like the original CD again.  Nice dream, but it won't happen.

Read www.digido.com for more on the subject of the new industry standard overcompression.  The real solution is for the producers and everyone involved to stop playing the "My CD is louder than your CD," game.

Inverting Dynamics Compressor

Reply #3 –
Quote
Originally posted by gdougherty
Well, there really is no "industry standard" compression settings, it's completely on a case by case basis, and up to the desires of the producer.

Overcompressed crap, unfortunately will remain overcompressed crap.  You could go through yourself with an expander on a song by song basis and try to play mastering engineer on the stuff you really like, but again, you might make some difference, but once the damage is don, it's done.  Kind like trying to make a 64Kbps mp3 sound like the original CD again.  Nice dream, but it won't happen.


There are multiple stages of compression.
The last stage should be invertable.
You can make statistics and find an inverse
compressor or hints where to use LPC prediction
to estimate real sample.

http://www.uni-jena.de/~pfk/mpc/clipping.html

<<Note that inserting URL do not work. I must
connect a mouse to the computer and must press the [Ok] button instead of pressing ENTER>>

Typical hard clipped CD:



Typical soft clipped CD:


Last is a sampler, and the original CD titles are taken and compressed once more.
--  Frank Klemm

Inverting Dynamics Compressor

Reply #4 –
Quote
Originally posted by Frank Klemm


<<Note that inserting URL do not work. I must 
connect a mouse to the computer and must press the [Ok] button instead of pressing ENTER>>


I just tried it and it works fine with Mozilla 1.0 RC2, IE6, and Netscape 4.7.  Not sure why you can't get it working.  Are you still using Netscape 4.x on Linux?

You can always just type the url code in also.. it's pretty simple:

[ URL=x]y[ /URL] (without the spaces)

Where x is the url and y is the link text.

Also, you can just paste the url and the php will parse it into a link automatically.. you only need the url tag if you want to use special text for the link instead of the actual url.

Inverting Dynamics Compressor

Reply #5 –
You can gain a cpl of dB of headroom by expanding the <200 Hz. It is very tricky. If you get it right, it may sound as a kickdrum.
Oh and all those mastering engineers and producers should be hanged!:diabolic:

Inverting Dynamics Compressor

Reply #6 –
i know this may be somewhat off topic, but it has to do w/ dynamic audio compression.  i was wondering if there is some way to reverse the dynamic audio compression that is applied by FM radio stations when broadcasting?  is this feasible or not, and if it is, how might i be able to do this?
 

Inverting Dynamics Compressor

Reply #7 –
Quote
Originally posted by ProtectYaNeck36
i know this may be somewhat off topic, but it has to do w/ dynamic audio compression.  i was wondering if there is some way to reverse the dynamic audio compression that is applied by FM radio stations when broadcasting?  is this feasible or not, and if it is, how might i be able to do this?
I'm guessing that each radio station keeps a constant amount of compression going on their signal (rather than changing it for each song) so theoretically you could extract the original (over-compressed) recording of the song by reverse-engineering and undoing the compressor.

The problem comes from radio's really stupid "Zero Headroom Policy" (I don't know the right term for it). All radio stations pump the signal as high as possible, with a ~3 second release time, so whenever a quiet passage is played, the gain goes way up (so the loudness is the same), and then when the source gets loud again there's a whole lot of clipping until the signal recovers. In my opinion this is the worst part of mainstream radio broadcast, and I don't think you can use dynamic expansion to recover the clipped and distorted sound, nor could you really fix the "Zero Headroom" because you wouldn't know how much to attenuate the signal to keep the volume true to the original.