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De-clipping filter
https://forums.stereotool.com/viewtopic.php?t=3595		 Page 2 of 6
Author:  hvz [ Fri Mar 25, 2011 3:34 am ]
Post subject:  Re: De-clipping filter
The static is not completely gone yet, but it has been reduced quite a lot. (I still don't know exactly what's causing it, I just added some information about the input signal that I didn't use before).

Teaser #2:
Original: http://www.stereotool.com/temp/original ... PPEDx4.wav
After declipping: http://www.stereotool.com/temp/01_origi ... PPEDx4.wav

Note: The Original is the recording that I used - if you have another declipper that you use, you can feed it through that to see if it gives better (or worse) results. Clipping level is at 1/4th of the maximum level (+/-8191).

I've tried some 'real world' clipped signals, but due to the tilt in what I've tested so far that didn't work very well. I really need to figure out what this tilt is...
-- Edit: Ok, tilt seems to be exactly what 'Stereo: Stereo Image: Phase' does. So that's easy. :D
Author:  hvz [ Fri Mar 25, 2011 4:47 am ]
Post subject:  Re: De-clipping filter
Note: I have just re-uploaded the 2nd file after adding a static filter :-)

Sounds that are a lot (too much) louder in the restored version than in the original are reduced now.

This removes most of the static. But I still need to check:
- If I can prevent it from being created in the first place (probably not completely!)
- With or without you: Loud bass disturbs 'S' sounds too much (most other sounds are restored very well!). This is probably very difficult to solve (has something to do with the nature of 'S' sounds).
Author:  Bojcha [ Fri Mar 25, 2011 1:39 pm ]
Post subject:  Re: De-clipping filter
http://www.claessonedwards.com/forum/vi ... f=5&t=1754
Author:  hvz [ Fri Mar 25, 2011 11:42 pm ]
Post subject:  Re: De-clipping filter
Static problem is fixed! And that also seems to have improved the filtering itself.

I've re-uploaded the 2nd version, the result is now really spectacular!
Author:  hvz [ Sat Mar 26, 2011 12:07 am ]
Post subject:  Re: De-clipping filter
Quote:
http://www.claessonedwards.com/forum/vi ... f=5&t=1754
Hm, that's something completely different...
Author:  Bojcha [ Sat Mar 26, 2011 12:16 am ]
Post subject:  Re: De-clipping filter
well .. i can only say .. this is fantastic!
Author:  hvz [ Sat Mar 26, 2011 2:27 am ]
Post subject:  Re: De-clipping filter
What is left now is how to determine which samples are clipped and which are not. For these samples it's easy (I clipped everything at the same level). That's also what you get when you directly rip a CD. But in MP3s things may look very different.

Bojcha: About Nelly Furtado track: This thing has 'Tilt' again... :(

Anyway, I tried the following:
1. Boost the volume by 50% (this introduces a lot of extra distortion)
2. Then pass it through Stereo Tool's declipping filter

Result seems to sound slightly better than the original this way. So if I manage to get the distortion detection to function properly (handle tilt) it should really improve.

I've also tried Katy Perry - Firework, but I don't even see any clipping there :roll: Still it sounds horrible.
Author:  Bojcha [ Sat Mar 26, 2011 2:39 am ]
Post subject:  Re: De-clipping filter
That's what i say.. Nelly Furtado track, .. SeeDeClip also do nothing with that track!

Try Laddy Gaga - Alejandro .. There is one "drum" constantly in clip... what will filter do there... ?

What's important is to have "Tilt" aka "Phase Difference" on input.
Why?
If i play Some track on PC1 and that goes to mixer and master from mixer goes to another PC with ST.. Big chances is that "Tilt" is changed!
So, on input is easy to adjust that "tilt" with some test tone like 50Hz square, using "input scope"
That way we are sure that input signal has no "tilt" and "de-clip" filter will do better clip analyze.
Author:  hvz [ Sat Mar 26, 2011 2:48 am ]
Post subject:  Re: De-clipping filter
Hm, lacking a better idea I think I'll go for:
- A suddenly appearing and disappearing relatively flat area at a high amplitude.
I'm going to treat any pixels that match that description as 'clipped'. (Correcting tilt might be a better idea, but so far it seems that the tilt changes even during the same track... Either that or I'm doing something wrong - like using the wrong 'tilt' algorithm).
Author:  hvz [ Sat Mar 26, 2011 2:53 am ]
Post subject:  Re: De-clipping filter
Idea #2: Add a 'did I actually improve anything?' filter - if something was seen as clipping, and fixing it did not improve the audio (get rid of clipping noise), revert to the original signal.
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