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What? Ffp not reliable??


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I always thought that FFP (FLAC fingerprints) was a reliable and tested way to check if my music files were backed up properly, and not degraded in any way I use them. I put great emphasis on that, since I already, in the past, lost all my music files due to simultaneous two disk drives malfunction. Since then, I've become Mr Back-up personalized. But how to be sure that my back-ups are OK? FFP was it for me.

 

Couple of days ago, I experienced something really disturbing. I bought a couple of hires albums on Qobuz, Jackie McLean's One Step Beyond to name one of them. FLAC files. Began to play them. Big problem occur at the 2:45 mark on the 1st file, then again same kind of problems (like a sampling problem) on the 2nd file.

 

Not very happy, I downloaded the same files again, in WAVE. Played them. Perfect. OK. Encoded them in FLAC. Probably some problem on the Qobuz side. Or so I thought.

 

Before replacing the old downloads with the new ones, I decided to run the FFP of the old downloads on the new ones, just to see if the other files of the album had the same kind of problems as well.

 

Well well. For my FFP checker (Trader's Little Helper), the FFP of the faulty file was the same as the "sane" file.

 

To be sure, I played each of them again. The faulty one continue to have the same weirdness at the same spot. The new one continues to play well. But for TLH, they have the same audio content.

 

Wots the buzz???

 

Since you may be curious about it, I use Windows 10 and JRiver 19. And Trader's Little Helper 2.7.0 (build 172)

 

PS

Further analysis. Both of my faulty files returned an error with the "Test encoded files" function in TLH. "File is corrupted or otherwise corrupt" is the message.

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But what disturbs me is that it still returns the same checksum as a sane file.

 

The sane file could be corrupted but a glitch in the wav file would probably be inaudible (one bad sample, may be ignored / compensated in the DAC)? While it may prevent proper decompression of the flac? And still have the same checksum.

 

G.

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Only corrupted files, during coding (I doubt... in theory it is possible if the Verifiy function is not activated) or download.

 

What happens is that flac fingerprint files are not as suitable to verify data integrity. See here:

When you generate a flac fingerprint file, it is merely a readout and compilation of the internally stored checksums from each of the flac files.

-In FLAC files the md5sum of raw audio data is stored as metadata

-When you create fpp files, just copy this metadata in a text file

-"Verification" consists of comparing metadata "md5sum" embedded in the FLAC files, with which it is written in the fpp file (I think it was designed for P2P networks)

-As seen this "verification" says nothing about the actual content of the file. Just comparing two lines of text...

-To verify the integrity of the audio data must use the test function (compares the md5sum metadata with the md5sum of real audio decoded - decoding is in memory, no data is written - ) with the program you use, with flac command line, shntool, etc...

 

Sorry for my english

[...] "Do fathers always know more than sons?" and the father said, "yes". The next question was, "Daddy, who invented the steam engine?" and the father said, "James Watt." And then the son came back with "- but why didn't James Watt's father invent it?"

Gregory Bateson

Steps to an Ecology of Mind (...)

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