[music-dsp] Reversing dynamic range compression in music

[James Chandler Jr]

----- Original Message ----- 
From: "Bogac Topaktas" <bogac at bteaudio.com>
> James Chandler Jr wrote:
>>If a lot of your modern final mastering gain-boost, depends on a multiband
>>compressor with program-adaptive release, feeding a final lookahead 
>>peaklimiter
>>with program-adaptive release-- Maybe that would be tricky to reverse without
>>knowing the parameters of the original mastering chain?
>
> Even knowing parameters may not help since almost every multi-band compression
> algorithm has a unique frequency-selective/program-adaptive response. It would 
> be
> great if CDs contain a phrase like: "Heavily compressed with xxx 
> device/plug-in with
> the following parameters" in the inside cover:)

Yes, perfect reversability might be impossible even if you did know what 
equipment did the original squashing.

A deadly-effective peak limiter might eliminate all traces of clues which one 
might use to recover the original.

I'm not familiar with the current crop of limiters. Awhile ago devised a 
peaklimiter that works good enough for my desires, and always use that one, but 
I don't have time lately to do much audio. All time is spent programming.

Mine uses program-adaptive envelopes such that even if the gain is high enough 
that the unit is always in limiting, in that case the release time will become 
long enough that there are still some dynamic cues in the music.

That extreme amount of limiting would pump obnoxiously in my plugin, but some 
dynamic variation in the signal would leak thru. And the side-effect of that, is 
that my peaklimiter won't ever get quite as loud as a device that is always 
balls-to-the-wall. Completely flattening the dynamic range wasn't ever a design 
goal (grin). I just wanted to avoid accidental clipping and not sound bad.

Just saying, that some compressor/limiters might allow enough variation to leak 
thru, that an expander could successfully widen the dynamic range. But the 
expander output wouldn't necessarily resemble the original signal.

That was also the case with the old Vinyl expander gadgets.

Back in the 1970's, did an elaborate stereo install gig for a wealthy audiophile 
who had one of the DBX dynamic range expanders which had several sliders, 
several opportunities for adjustment. The customer prized the box, but to my ear 
it just made the records sound 'ragged and uneven', not 'better'.

>>Perhaps the best one could do, would be to make a plugin or program with
>>multi-band expansion, and lots of knobs to play with?
>
> Here is a small list of commercially available multi-band 
> compressor/expanders:

Great idea, to use an already-existing plugin/program. I was probably thinking 
that if trying to sell a 'dynamic range recovery' product to audiophiles, maybe 
it would be configured a differently than a generic compressor/expander. More 
'specialized' or 'easier' for the task.

jcjr