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un-deleted mp3's = lower quality?
rlbest
post Dec 21 2010, 20:37
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The other day I deleted about ten gig of MP3's by mistake. I quickly realized my mistake and was able to recover most using some undelete software. (I forget which. Laptop is at home and I'm on my phone right now.) The files play fine and sound normal, so my question is mostly academic as far my ears go. Does deleting and restoring audio files lower the quality? My guess is no, but I was curious.


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pdq
post Dec 21 2010, 20:40
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If any errors were introduced by undeleting the files, the change would not be subtle. I think your files are just fine, but there are software applications that can test mp3s for corruption.
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sauvage78
post Dec 21 2010, 22:12
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It depends on if wether or not the space used for the mp3 was overwritten by other data or not, even if you recovered just after the deletion, as the system regulary write small files to the system HDD, if the mp3 were on the system HDD, then yes there is a possibility of corruption. Then the longer you waited, the higher is the corruption possibility. Anyway as the files regulary written by the system are small the number of corrupted mp3 should be small. The problem is in case you have written additionnal data to the disk before trying to recover, then a lot of mp3 might be damaged (overwritten).

I had the problem once with flac, thks to MD5 I was able to recover 99% of my files (I didn't overwritte). Without checksums I doubt that it would be that easy, it might seems easy but you will not have the same confidence on your files anymore. With the right softwares, some stream errors might be checked but maybe not all possible errors, I dunno.

Last time I used them, recovery data softwares (Like GetDataBack For NTFS) just changed a 0 or a 1 in the file header, so it is not the recovery software itself that is faulty but the linked data which is not there anymore if it has been overwritten, well as far as I understood. Happily I didn't used this kind of softwares for years now wink.gif

PS: Anyway trying to recover doesn't lower audio quality, it only corrupts by recovering random data. Corrupted mp3 should have glitches, sound garbage, or not even play at all. It will most likely not just sound bad. ABXing is not really efficient here, on such a large scale its wether you have checksums ... or not.

This post has been edited by sauvage78: Dec 21 2010, 22:36


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Porcus
post Dec 21 2010, 23:01
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QUOTE (pdq @ Dec 21 2010, 20:40) *
If any errors were introduced by undeleting the files, the change would not be subtle. I think your files are just fine, but there are software applications that can test mp3s for corruption.


Indeed. However, a few applications seem to write fairly dirty mp3 files, so there might be a few false positives. Better find one which can distinguish between corruption and inaccurately reported length.


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