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Knowing if a CD/wav comes from Ogg ?
Xrcr9709
post Feb 24 2012, 02:19
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Hello,

I some special tape in the past, like 10 years ago. I encoded it in Ogg Vorbis, accidentally deleted the .wav files.

Now I have juste found back a CD with the same content.
But I don't remember at all if the CD has been burnt from the original wav files or from the already encoded Ogg files.

I there a way I can be sure about that ?


Thank you for your help.
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saratoga
post Feb 24 2012, 02:21
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No. You're out of luck without the original to compare it to.
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DVDdoug
post Feb 24 2012, 02:47
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There are a couple of programs that try to analyze a file to determine if it's ever been lossy-encoded. I've never tried any of them... One is the Tau CD Authenticity Analyzer.

If the CD sounds obviously different, it's probably from an original (or from a different lossy copy smile.gif ). If it doesn't sound obviously different, you can't be sure.

If the OGG file sounds OK, maybe it doesn't matter... Often, we can live with "good enough".

If it's absolutely critical for you to have a non-lossy copy, I guess you'll have to buy the CD.
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AlexDDR
post Feb 24 2012, 02:49
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is more easy if the ogg file are in a low bitrate due to the differences are more evident with the original

if you analize in adobe audition for example in frecuency spectrum view and look for de lowpass limit, for q4 (128kbps) is 18000hz
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zima
post Feb 24 2012, 02:57
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Not necessarily, saratoga? How precisely defined is Ogg Vorbis decoding? I hear it is very carefully defined for MP3 - compliant decoders giving the same output, within rounding tolerances...

...if that's also the case for Vorbis, and if you, Xrcr9709, also still have those Ogg Vorbis files (sounds like you do; otherwise, there would be even no point in asking, since the found CD would be your only copy anyway) - wouldn't comparing the output of Vorbis files and CD possibly do the trick?
If the spectrum (or such) are identical - or very nearly identical, to account for rounding - then the CD came from the PCM output of those Vorbis files. If clearly not identical, then... well, we still can't know, on that information alone, that the CD came from WAV - but if Xrcr9709 roughly remembers what he was doing with those files (for example, that there was only one lossy encoding done), this info could be enough of a circumstantial evidence, I guess?

edit: but anyway, if you can't hear the difference... (this place calls for ABX testing after all tongue.gif )

This post has been edited by zima: Feb 24 2012, 03:02


--------------------
http://last.fm/user/zima
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Xrcr9709
post Feb 24 2012, 03:08
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I've just tried to ABX it but it seems that the ABX component I've user for Foobar2000 work terribly bad ... looks like it's always resetting the count ... Or there's something I missed ...
And anyway, it sound difficult to ABX.

Actually, there is no CD or any commercial way to buy this recording, otherwise I wouldn't bother.

The Ogg files are at very low bitrate, but the original was a tape that was also at rather low quality.

QUOTE
if you analize in adobe audition for example in frecuency spectrum view and look for de lowpass limit, for q4 (128kbps) is 18000hz

There, I'm lost ... And I don't have Adobe Audition, I only have Sony Sound Forge and Audacity.
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Xrcr9709
post Feb 24 2012, 03:15
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Trying to undestang something to spectrum analysis, but at least, I would need lowpass limit for q3 (112kbps). That the quality I used in those days ... sounds pre-historic to me now ...

This post has been edited by Xrcr9709: Feb 24 2012, 03:15
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Xrcr9709
post Feb 24 2012, 03:26
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Using Sony Sound Forge:

Zooming at the graphs in the basic sound editor, they look very very similar.

Now, trying stuff with the spectrum analyser, keep the same settings and switching for one version of a track to the other, I see differences, but I have no idea what they mean of if they are meaninful.
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saratoga
post Feb 24 2012, 03:37
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QUOTE (zima @ Feb 23 2012, 20:57) *
Not necessarily, saratoga? How precisely defined is Ogg Vorbis decoding? I hear it is very carefully defined for MP3 - compliant decoders giving the same output, within rounding tolerances...


Oh I thought he didn't have the Vorbis files anymore. If he has them, then yes, that will work. Decode the vorbis to wav, then compare it to the PCM from the CD. If its nearly identical, its lossy.
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AlexDDR
post Feb 24 2012, 03:57
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QUOTE (Xrcr9709 @ Feb 24 2012, 03:26) *
Using Sony Sound Forge:

Zooming at the graphs in the basic sound editor, they look very very similar.

Now, trying stuff with the spectrum analyser, keep the same settings and switching for one version of a track to the other, I see differences, but I have no idea what they mean of if they are meaninful.



in audacity i did the test with a tape recorded in 1973 (it's a child tale)

the menu in spanish is: Analizar --> Dibujar spectro

only the first 23.8 seconds are allowed due to audacity limits

wav captured



and q3 ogg transcode


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Xrcr9709
post Feb 24 2012, 04:24
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Ok, after analysing frequencies with Tau and Audacity. I think I can conclude that the CD was burnt out of Ogg Vorbis. Thank you all anyway.
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Xrcr9709
post Feb 24 2012, 04:27
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But actually, since it comes from a tape, ... what are the highest frequencies possible on a tape ?
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AlexDDR
post Feb 24 2012, 04:43
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QUOTE (Xrcr9709 @ Feb 24 2012, 04:27) *
But actually, since it comes from a tape, ... what are the highest frequencies possible on a tape ?



i think that high frecuency is only noise
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Xrcr9709
post Feb 24 2012, 04:48
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Probably, but if I'm trying to analyse if high frequencies are there ... I should first be sure that they actually should be there.
I mean it have lower "higher frequencies" than Ogg Vorbis, that test would be pointless.
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