Is it possible to uncompress audio?

farss wrote on 1/17/2004, 5:42 AM
I suspect I know the answer to this and it's going to be "No" but I thought I'd ask the experts.
I have an audio track taken from VHS so it isn't too flash to start with audio or video wise, the video I can live with and the client isn't expecting miracles but it would be nice to give him a pleasant surprise.
It's full on opera, big orchestra and a dozen singers, looks like some effort was made to get a decent recording judging by the number of mics but it sounds like its been through more compression / limiting than was good for it, sounds like a wall of sound, not a wall of music.

I'm guessing that to have any chance of restoring any dynamics I'd have to duplicate the same set of parameters used in the compression. I've tried using Graphic Dynamics but before that seems to produce any improvement the audio starts to fall apart.

Any advice (including not a chance!) much appreciated.

Comments

Rednroll wrote on 1/17/2004, 9:49 AM
Try an "expander". A compressor, compresses the dynamics range, while an expander "expands" it. Don't expect miracles like you stated, but this may be your best stab at an improvement.
farss wrote on 1/17/2004, 2:05 PM
Thanks Red,
I am old enough to remember those compression/expansion ideas that were all the rage a few decades ago and I also remember that the trick was getting the expansion to precisely track the compression and even then there was much argument over the wisdom of doing such things.
zork1341 wrote on 1/17/2004, 10:56 PM
Sorry, but I can't think how an "expander" would improve your recording. As you describe, the dynamic range (ie. the level difference between the "softer" and the "louder" parts ) of the VHS recording is minimal.

An expander is not a "magical-dynamic range-expander", it just applies a fixed reduction in the signal level triggered when it goes under the "threshold" level. The amount of reduction is set with the "expansion ratio", being infinite the equivalent of a gate.

If your program level is flat (always loud) the expander would not detect any level change, thus not applying any level reduction at all.

I think the only solution is to apply some automated (level curves) dynamic changes to the whole program, trying to emulate the natural dynamics of the pieces. Maybe some eq'ing or filtering would add some more softness in the mix.
zork1341 wrote on 1/17/2004, 11:25 PM
I would recommend also the Waves Trans-X plugin (Trasform bundle), fantastic tool for shaping transients, even in stereo programs ... give it a try. It can bring some "air" back in very over-compressed material.

Good luck ...
farss wrote on 1/17/2004, 11:47 PM
Thanks,
I'll have a look at it.
Rednroll wrote on 1/18/2004, 10:37 AM
"I think the only solution is to apply some automated (level curves) dynamic changes to the whole program, trying to emulate the natural dynamics of the pieces."

Zork,
You just described what an "expander" tries to accomplish. A typical use for the expander was to get back some of the dynamics due to over compression.

"If your program level is flat (always loud) the expander would not detect any level change, thus not applying any level reduction at all."

Nothing is totally flat, so It would take some playing around with the right threshold value to get back some of the dynamics. With the use of Vegas's automated FX, you could even automate the threshold to give you better results.

"An expander is not a "magical-dynamic range-expander"
Thus, I said "don't expect miracles"
zork1341 wrote on 1/19/2004, 1:22 PM
Red,

What I meant was that if the music is very-over-compressed-and-limited, the expander would not find any useful "clue" to accomplish its work, as the original dynamics and transients are modified, surely obtaining only hard and machine-like results.

It's true you'll get better results using some threshold or parameter automation, but to deliver some real and musical results in this scenario, I'm sure you'll not find any better tool than your ears and personal musical sensibility ... and vegas ;)
farss wrote on 1/19/2004, 6:07 PM
Well,
I took all the advice on board and just added a volume envelope so the passages that obviously should have been a bit quieter are now a bit quieter and left the big finale where it was.
To my totally untrained ear it sounds a lot better, still far from perfect because so much of it got muddied along the way but now there is some dynamics to it.
Gievn my lack of experience and the amount of money in the job I think that's about as much as can be done.

One of the other tapes to go on this showreel had the audio 10 frames out of sync, fixing that sure improved the sound. Funny how the brain works, I didn't change the audio itself per se but getting it back in proper sync stops the brain focussing on something being wrong but not quite certain what.
tmrpro wrote on 1/20/2004, 7:21 AM
Try the Waves C4, it has a preset that is called decompressor. It is basically frequency and dynamically relative expansion. I've used it before and in certain cases, it works pretty well. It'll just depend on how much of an overall solution you really need.