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Q: improving sound of old .mp3 files by filtering artifacts?
Porcus
post Jan 3 2012, 16:33
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Before shouting «no, you cannot know what has been deleted»: this is not about knowing, it is about guessing better than one could once upon a time in the previous millennium.


Back in the 90's, you could way more often than today single out an mp3 file by its artifacts (for given bitrate in suitable range [*]). Of course we could not know without the original whether a certain signal is an encoding artifact or is part of the music, but back in those days we could fairly often make an educated guess by listening -- doing «ABX except without the A and B».

So, the last 15 years have brought forth lossy encoders which are better at avoiding audible artifacts: Not only do we know better what to avoid, we also know better how to avoid it. And in principle, it might very well be possible to use this improved knowledge to (i) detect in an old mp3 file «what would have been avoided today», and (ii) filter it out. Not to achieve the impossible certainty that this part of the signal was not in the original source, but to achieve fewer audible nuissances more often than not.


Q: Has this been attempted, successfully or not?


(Any such tool could be easily testable if one has an old encoder and a lossless source and a few good ears.)




[*] I presume that http://listening-tests.hydrogenaudio.org/s...8-1/results.htm should keep TOS#8 moderation off my back.


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Gumboot
post Jan 14 2012, 11:07
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For badly encoded voice you might try recompressing it with a speech codec to see if that is forced to throw away some artefacts it considers unencodable.
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