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Topic: Removing (or reducing) clipping with Audacity, Adobe Audition or the l (Read 39028 times) previous topic - next topic
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Removing (or reducing) clipping with Audacity, Adobe Audition or the l

I'm looking for a good tutorial (for Audacity, Adobe Audition or any other program like that) that would help me to remove or reduce clipping on albums such as Metallica - Death Magnetic or Rush - Vapor Trails.

Anyone can help ?

Thanks !

Alan

EDIT: The missing part in the topic title is "or the like"

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #1 –
Audacity has the ClipFix Plugin. I'm not sure how good a job it does, but you can find out, i guess.

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #2 –
http://help.adobe.com/en_US/audition/cs/us...3598d-8000.html

Here is the Adobe page with "De Clipper" for CS6. The info for Audition 3 is very similar. I have used it the way you're asking just with different material. In Audition 3 you'd select  Effects>restoration>clip restoration(process). Select how badly it's clipped. "Lightly" drops the level 4 dB and then 'fills in the blanks'. "Heavily" does the same but with a 12 dB gain drop. In my opinion it's not dramatically different but an improvement in the dynamics. Play with it. It's how you learn. Once the audio is clipped there is no 'correct' way to undo the damage but you can reduce the side effects.

G²

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #3 –
Thank you both for the replies, much appreciated.

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #4 –
Relife is a little VST plugin that does a very good job at restoring the dynamics of heavily clipped audio. It can be used with Audacity, Audition, etc.

And it's free.

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #5 –
ReLife is useless: it makes the waveform appear better, but does not change the sound: all the distortion is still there.

I recommend the Declipper from iZotope RX.

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #6 –
Quote from: Alexey Lukin on
I recommend the Declipper from iZotope RX.
surprise  (being a DSP developer at iZotope Inc)
Alexey, are there methods to objectively test declipper quality ? IME most restoration engineers base their judgements on how the result sounds to them. That's fine but this is HA

Would this be a fair test?:
1-deliberately clip an unclipped signal
2-restore clipped parts with declipper DSP
3-compare declipped signal to original (level matched)

There will most likely be an audible difference, so how can we objectively judge its relevance ?

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #8 –
Quote from: Alexey Lukin on
ReLife is useless: it makes the waveform appear better, but does not change the sound: all the distortion is still there.


That's my experience with the clipping corrector in CEP 2.1/Audition.

If I think about the problem that is being solved, I can see how effective solutions may be elusive.

Basically, a chunk of signal is chopped off and gone forever. Our challenge is to guess what it was.  Problem being, the source of the chopped-off info is a variety of sources, each with its own harmonic structure, etc.

Back in the day people used the saturation of analog tape for a similar purpose, and it could work.  They would overdrive analog tape so that its fairly soft perhaps even euphonic saturation curve which was both frequency and amplitude sensitive replaced the sharp-edges effects of electronic clipping.

My other thought is that intelligent software could make some determinations about the target response by analyzing non-clipped segments.


Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #9 –
Quote from: Arnold B. Krueger on
If I think about the problem that is being solved, I can see how effective solutions may be elusive.

Basically, a chunk of signal is chopped off and gone forever. Our challenge is to guess what it was.
...same as declicking old records, and that's a solved problem.  Difference is, clicks are rarely systematic, whereas clipping is.

This declipper might be useful...
http://www.hydrogenaudio.org/forums/index....c=99917&hl=

Cheers,
David.

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #10 –
Declipping, as an interpolation/reconstruction problem, will never give you perfect results. We do have audio interpolation algorithms that do a reasonable job but I think it's an exaggeration to call any such thing a "solved problem."

The audacity clip-fix plugin others have mentioned, which Ben Schwartz wrote as a one-off back in his undergraduate days, will do a moderately reasonable job for mild clipping but that's it. It just fits a cubic spline to the edges of the clipped regions. That takes little very little context into account-only a couple samples before and after each clipped region- and a cubic spline is not a great fit for e.g. sinusoids except over a very short window. It is also rather slow for what it does (memory management issues, limitations of Audacity's Nyquist interpreter).

If you only had isolated instances of clipping you'd likely get better results by using Audacity's repair tool, which uses least squares autoregression to interpolate.

Postfish, from Monty of Xiph.org, does a vastly superior job of declipping and has a number of other useful tools too (for instance, I've usually used compression/soft limiter in conjunction with declipping so I can get a less-distorted version without reducing the gain all that much). The only downside is that it only runs on *nix and so if you're on Windows you'll need to use a VM.

I haven't looked into it enough to understand its declipping algorithm well; Monty gave a brief blurb in his original announcement.

Monty hasn't had a lot of time to work on Postfish in recent years, and sure, it could use some polish, porting, and documentation. But it works well, and despite his lack of time Monty still fixed a bug I reported within a day.

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #11 –
Quote from: Kees de Visser on
Would this be a fair test?:
1-deliberately clip an unclipped signal
2-restore clipped parts with declipper DSP
3-compare declipped signal to original (level matched)

Yes, this is totally fair! It would be nice to make an objective test of declippers. In practice, clipping is not always “digitally perfect”: sometimes there's some ringing around the clipped parts, sometimes clipping is “soft” or asymmetric in level. But this simple test still makes sense for evaluation of interpolator quality.

I can propose a couple of samples that I used for my own tests. One has been manually clipped @ –12 dBFS from a clean ground-truth recording. Another one is a real-life clipped recording that has been sent in for restoration and does not have a ground truth. Would anyone like to process these with –12.1 and –9.3 dB thresholds and submit here?

Sarah.wav
Sarah_clipped.wav
Piano_clipped.wav

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #12 –
Although it isn't always true, most clipped material is clipped at 0dBfs. 0dB is the  target amplitude across the entire track. If the maximum amplitude of the clipped material is 0dB + XdB, the entire track needs to be amplified by -XdB before "fixing" the clipping if the goal is to make any pretense of restoring what was there before it clipped. Without that step, the process can be nothing more than just the introduction of some different, but hopefully better sounding, distortion in the local of the clip.

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #13 –
I intentionally reduced the level of tracks to allow for level matching of ground-truth vs. clipped vs. declipped tracks. If some declipper requires a 0dB clipping point, please return the output signal to the original level for comparison.

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #14 –
Careful level-matching must be done when comparing versions.

I suspect that RG and R128 values will be useless in this endeavor.  Undoubtedly someone will probably calculate these numbers anyway, in which case please also supply DR values.

Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #15 –
Quote
Metallica - Death Magnetic or Rush - Vapor Trails.
I don't know the details of how those albums were mastered, but typically it's not only volume-boost clipping.    It's not like there was just some accidental clipping, and you need to restore peaks...      There's probably a ton of compression (probably multi-band compression) and limiting.  Then, there's probably some EQ to hide some of the damage.    I assume the hard-clipping is the result pushing too much gain into the limiter, but it's also possible that as the last step they add a couple more dB, pushing the peaks into  (or further into) hard-clipping.

Quote from: Arnold B. Krueger on
Back in the day people used the saturation of analog tape for a similar purpose, and it could work.  They would overdrive analog tape so that its fairly soft perhaps even euphonic saturation curve which was both frequency and amplitude sensitive replaced the sharp-edges effects of electronic clipping.
Interesting!!!!  Adding more clipping (but soft clipping) to repair hard-clipping!  But, that approach is unlikely to improve the overall sound of a "loudness war" CD.

Re: Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #17 –
Better late than never.

Your question needs to be more specific, i.e. clipping can produce any number of undesired effects (distorted sound, crackling audio, loss of fidelity/intelligibility, etc.), so it depends on your desired end result.

In Audition I often use several options:
1.  Use the "frequency splitter" function, split the track(s) in question into several different different tracks of different frequencies.  This will allow you to manipulate the individual bands, reducing volume of offending bands, or applying filters to remove the undesired effect from clipping.  Works well for crackling noises, and/or overloaded frequencies.
After repairing the individual bands, remix the several tracks of individual bands back into one single track.

2.  Another fix for crackling noises from clipped digital audio in Audition is to use the Restoration ->Remove Clicks/Pops feature (usually for removing clicks/pops from records, but works well on crackling from clipped audio too).

I can't speak enough of the "frequency splitter" function in Audition.  It takes a little time, but you can work wonders.

  

Re: Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #18 –
My success with declippers seems to be inversely proportional to the necessity, and obviously, severity of clipping.

But I have a somewhat related if inverse question.  I occasionally need a clipper, ideally one with adjustable threshold and "hardness". Yes, deliberate clipping.  Like the DSP equivalent of a pair of biased diodes. Basic search hasn't turned up much. Any ideas? As always, low cost is nice, free is great but it still has to work.

My crude solution is to apply gain until peaks I want to clip get forced above 0dBFS, then take the gain back out (Audacity does this better than Audition). But there's no hardness control, it's just a hard technical clip.

Re: Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #19 –
Audacity's limiter was improved recently, and there are now 4 basic options (and some other settings).   The old limiter was basically a clipper and that option is still available as  "Hard Clip".

If that doesn't work for you, there are lots of compressor/limiter plug-ins and you should be able to find something you like.

Re: Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #20 –
Apologies for the thread resurrection, in answer to the

"or any other program like that)"

bit of the question and in view of the audio declipping mention in the thread, there is a new version of SeeDeClip now available, called SeeDeClip4.

The useful (free) thing this offers is a total analysis of your music library in terms of 'mastering quality' so you can choose the best tracks to play. Many tracks are duplicated in 'Best of', 'Greatest Hits', 'Driving Rock Songs' and 'Remasters' (usually the ones to avoid), so this quality measure can be very useful to allow you to avoid the heavily damaged tracks and pick the good ones.

It does other stuff too - but in practice - as noted above - the best method of declipping is 'avoidance' - by listing the quality of all  tracks it's very useful for that. Note that it analyses stuff in the background so you'll need to leave it a while to analyse your whole collection.

Available here: http://www.cutestudio.net/

Please note: It's new so some bits may still need fixing and most people seem to struggle to install it for reasons I'm still investigating. The depressing part is how low the general quality of digital music is these days so careful you don't end up just listening to old 'Floyd and Genesis :D
Creator of the SeeDeClip4 multi-user Declipping Music Server.
Download your free copy now.

Re: Removing (or reducing) clipping with Audacity, Adobe Audition or the l

Reply #21 –
Quote from: CuteStudio on
,,, The depressing part is how low the general quality of digital music is these days so careful you don't end up just listening to old 'Floyd and Genesis :D

I don't see a problem with that. :D
Regards,
   Don Hills
"People hear what they see." - Doris Day