Fixing audio distortion

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Fixing audio distortion

Postby TVVCR » Thu Mar 27, 2008 1:56 am

I have a song that is badly distorted. Looking at the waveform reveals that the audio is so loud that it clips (this is just a small portion). If you're wondering it sound awful (http://cid-2c7b1875b1797362.skydrive.live.com/self.aspx/Audio%20-%20Public/distorted.mp3)

Image

How would I lower the gain and apply an amplitude modulation for the clipped waves?
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Postby DougDbug » Thu Mar 27, 2008 1:15 pm

Well... There are clipping repair programs. There is a free one called DeClip, I think Sony Sound Forge has a clip repair tool, and maybe Adobe Audition has one too.

I've never actually tried any of these. You may get some improvement, but I doubt they will be able to "fix" your file. Once a wave is clipped, information is permanently lost and there is just no way to know the amplitude or shape of the original waveform. These repair tools can make estimates, approximations, and assumptions, in order to restore some missing peaks, but if the waveform is severely clipped, I'm not sure how much "restoration" can be done.
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Postby TVVCR » Thu Mar 27, 2008 2:24 pm

DougDbug wrote:Well... There are clipping repair programs. There is a free one called DeClip, I think Sony Sound Forge has a clip repair tool, and maybe Adobe Audition has one too.

I've never actually tried any of these. You may get some improvement, but I doubt they will be able to "fix" your file. Once a wave is clipped, information is permanently lost and there is just no way to know the amplitude or shape of the original waveform. These repair tools can make estimates, approximations, and assumptions, in order to restore some missing peaks, but if the waveform is severely clipped, I'm not sure how much "restoration" can be done.

I downloaded DeClip but I can't get it to work.

Microsoft Windows [Version 6.0.6000]
Copyright (c) 2006 Microsoft Corporation. All rights reserved.

C:\Users\*****>cd C:\Users\*****\Desktop\declip_2_3-0

C:\Users\*****\Desktop\declip_2_3-0>make.exe
DeClip FreeV2.3-0 written by Graham Wilkinson
Copyright (c) Graham Wilkinson 2004-2008, GPL licensed version.
Go to www.cutestudio.net for more information and programs.
Usage: declip -[nvqR] -[tmTpP(num)] [in.wav [out.wav]]
Declipping options
-tN: Only declip if there are more clips per minute (dflt: -t100)
-n: No declipping (dflt: false)
-mN: How flat is a clip, relative to a 16bit wav. (dflt: -m300)
Level options
Misc options
-v: Verbose (dflt: false)
-q: Quiet mode (dflt: false)
-R: Reverse the whole track so it plays backwards. (dflt: false)
-TN: Wdiff: audio file signal compare, with threshold (dflt: -T0)
-pN: Printing (start) (dflt: -p0)
-PN: Printing (stop) (dflt: -P0)

C:\Users\*****\Desktop\declip_2_3-0>declip Ham - New Style2.wav Fix.wav
'declip' is not recognized as an internal or external command,
operable program or batch file.

C:\Users\*****\Desktop\declip_2_3-0>
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Postby JackH » Thu Mar 27, 2008 7:13 pm

One thing you can try in Goldwave is its Compressor/Expander. You first need to lower the peak level to give yourself some headroom, something like -6dB for starters. You can then play around with the Compressor/Expander, using "Boost loud parts" preset as a starting point. The idea is to set the threshold slightly below the peak level, then fiddle with the multiplier setting to see if you can find something that sounds reasonably natural.

DougDbug is corect, though, there's only so much you can do. Your file might be too badly clipped for anyhting to help.
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Postby DewDude420 » Thu Mar 27, 2008 8:08 pm

While it is possible to technically fix the clipping, it won't help. Somewhere this file didn't just clip, it distorted..and it distorted on mostly the low-frequency high-power stuff..ok..bass.

While I've yet to run it through Adobe Audition's declipper and the Sony package I've got..I ran it through iZotope RX which has given me nothing but outstanding results the few times I've used it...and it's fixed the digital clipping on badly mastered CD's before...I ran both extreme digital and extreme analog clipping filters on this..and it's just so badly clipped and distorted you can't get a clean repair out of this. I'd trash the file and try to re-record...and if you can't...well this this as a lesson in dynamics and don't try to keep your VU meters so close to the red all the time.
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