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midwinter · Jul 15, 2002, 12:04 AM

Hi all.

A friend of mine came over this weekend with one of the craptacular bootlegs of Lord of the Rings in hopes that I could make it playable for her. While I could care less about the quality of that bootleg (my order for the DVD is already in place), one of the problems with it is that the audio is *horribly* overdriven, and I had absolute fits trying, just for my own edification, to make it sound better.

Most of my experience with dealing with audio comes from multitrack audio recording, and so I rarely run into a problem with audio being overdriven (i.e. I always just go back and re-record the track if there's a problem with gain). And while I'm pretty handy around a studio, I'm no *real* studio engineer....

And so I ask: *is* there any way to correct overdriven audio? I realize there's no way that it will ever sound perfect again, but is there some combination of filters, compression, and EQ that one uses to correct this kind of problem? I suppose I'm really asking whether or not overdriving a signal introduces certain correctable and reproducable elements that can then be filtered out.....

Just curious.

Thanks in advance.

Cheers
Scott

[ 07-15-2002, 01:06 AM: Message edited by: midwinter ]

nutbits · Jul 16, 2002, 01:35 AM

As far as I know, once the sound levels have gone over the max, you have noise not information. You've lost all the details that made the sound distinctive. From now own all the tweaking in the the world will only give you tweaked noise.

Dan Szwarc · Jul 16, 2002, 06:27 AM

If the audio was overdriven when recorded then it was probably clipping. Once it clips, there is no going back to a clean signal.

Clipping is when the signal hits a max and becomes distorted. If you reduce the volume of a clipped signal, you are merely make it quieter. The clipping is a part of the recording and cannot be removed.

Spheric Harlot · Jul 16, 2002, 08:09 AM

<blockquote>quote:<hr />Originally posted by Dan Szwarc:
If the audio was overdriven when recorded then it was probably clipping. Once it clips, there is no going back to a clean signal.

Clipping is when the signal hits a max and becomes distorted. If you reduce the volume of a clipped signal, you are merely make it quieter. The clipping is a part of the recording and cannot be removed.<hr /></blockquote>That said...

Part of what makes clipping so unpleasant is that clipped waves get nasty higher-harmonic components.

So, while you will never be able to restore to acceptable quality, running the audio through a low-pass filter may at least make it slightly more bearable, if muffled.

Best would be an inverted amplitude-following envelope, i.e. Filter wide open at low audio levels (which aren't distorted), then kicking in on louder passages to reduce the overtones produced by the clipping.

I have no idea if this is possible using standard VST plug-ins, but it darn well *should* be.

Reason, perhaps?

midwinter · Jul 16, 2002, 10:19 AM

<blockquote>quote:<hr />Originally posted by Spheric Harlot:
 <blockquote>quote:<hr />Originally posted by Dan Szwarc:
If the audio was overdriven when recorded then it was probably clipping. Once it clips, there is no going back to a clean signal.

Clipping is when the signal hits a max and becomes distorted. If you reduce the volume of a clipped signal, you are merely make it quieter. The clipping is a part of the recording and cannot be removed.<hr /></blockquote>That said...

Part of what makes clipping so unpleasant is that clipped waves get nasty higher-harmonic components.

So, while you will never be able to restore to acceptable quality, running the audio through a low-pass filter may at least make it slightly more bearable, if muffled.

Best would be an inverted amplitude-following envelope, i.e. Filter wide open at low audio levels (which aren't distorted), then kicking in on louder passages to reduce the overtones produced by the clipping.

I have no idea if this is possible using standard VST plug-ins, but it darn well *should* be.

Reason, perhaps?<hr /></blockquote>Thanks all! I knew there was no going back...I was just curious about how one might go about making the best of a bad signal. I'll play around with some low-pass filters to see what happens.

Thanks again!

Cheers
Scott

Spheric Harlot · Jul 16, 2002, 05:55 PM

<blockquote>quote:<hr />Originally posted by midwinter:
Thanks all! I knew there was no going back...I was just curious about how one might go about making the best of a bad signal. I'll play around with some low-pass filters to see what happens.<hr /></blockquote>Mind, I was just firing stuff off the top of my mind...there may be a better way of going about it (IANASEngineer).

Don't expect much, though.

-spheric*