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Improving ext4: bigalloc, inline data, and metadata checksums

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Nov 30, 2011 15:35 UTC (Wed) by pr1268 (subscriber, #24648)
In reply to: Improving ext4: bigalloc, inline data, and metadata checksums by Trou.fr
Parent article: Improving ext4: bigalloc, inline data, and metadata checksums

From that article: Mp3 to Ogg Ogg -q6 was required to achieve transparency against the (high-quality) mp3 with difficult samples.

I used -q8 (or higher) when transcoding with oggenc(1); I've done extensive testing by transcoding back-and-forth to different formats (including RIFF WAV) and have never noticed any decrease in audio quality or frequency response, even when measured with a spectrum analyzer. I do value your point, though.


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Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 1, 2011 22:54 UTC (Thu) by job (guest, #670) [Link]

Just to clarify for everyone (who perhaps stumbles in via a web search): converting from mp3 to ogg, or indeed any time you apply lossy compression to something already lossy compressed, can only make the quality worse. The best case here is "at least not audibly worse".

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 10, 2011 1:04 UTC (Sat) by ibukanov (subscriber, #3942) [Link]

When one approximate another approximation it is possible the result will be closer to the original than the initial approximation. So in theory one can get better result with MP3->OGG conversion. For this reason if tests show that people cannot detect the difference with the *properly* done conversion, then I do not see how one can claim that it can only made the quality worse.

Lossy format conversion

Posted Dec 10, 2011 15:20 UTC (Sat) by corbet (editor, #1) [Link]

Pretty far off-topic, but: it is a rare situation indeed where the removal of information will improve the fidelity of a signal. One might not be able to hear the difference, but I have a hard time imagining how conversion between lossy formats could do anything but degrade the quality. You can't put back something that the first lossy encoding took out, but you can certainly remove parts of the signal that the first encoding preserved.

Lossy format conversion

Posted Dec 12, 2011 2:54 UTC (Mon) by jimparis (subscriber, #38647) [Link]

You can't replace missing information, but you could still make something that sounds better -- in a subjective sense. For example, maybe the mp3 has harsh artifacts at higher frequencies that the ogg encoder would remove.

It could apply to lossy image transformations too. Consider this sample set of images. An initial image is pixelated (lossy), and that result is then blurred (also lossy). Some might argue that the final result looks better than the intermediate one, even though all it did was throw away more information.

But I do agree that this is off-topic, and that such improvement is probably rare in practice.


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