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Xing Header - Quality Indicator, Understanding VBR Quality
Iggy64
post Nov 23 2013, 19:28
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I rip CDs to FLAC and to mp3. For mp3, I use LAME with -V0 (best quality VBR). Generally, I find that the mp3 sound pretty much the same to me as the FLAC for the rock and even the jazz I typically play -- even on my better equipment.

Recently, I started looking more closely at the headers in my mp3 files, and got interested in learning more about the LAME header. The associated XING header - which is added with VBR encoding - contains a "Quality" indicator. When I use mp3diags to examine the XING headers for my files, it generally says quality=100, or sometimes as low as quality=97. At first I thought this was good. However, when I read up on the XING header spec, the I found that this 4-byte field is

"Quality indicator as Big-Endian DWORD
from 0 - best quality to 100 - worst quality (optional)"

I found similar references elsewhere. That is, there is agreement that 100=worst and 0=best.

I am baffled. I used the -V0 option. My files sound great (to me). How can they be "worst quality"?

Am I misinterpreting something here?
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lvqcl
post Nov 23 2013, 19:35
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http://gabriel.mp3-tech.org/mp3infotag.html#quality
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Iggy64
post Nov 23 2013, 20:51
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Thank you very much, lvqcl.

Very interesting! I'm glad that you have a reference with the reverse rating. It makes more sense, given how I encoded my files.

Several references have it the other way:

On that very same page you cited, just a couple of paragraphs above, it says

// ZONE A - Traditional Xing VBR Tag data
// 4 bytes for Header Tag
// 4 bytes for Header Flags
// 100 bytes for entry (NUMTOCENTRIES)
// 4 bytes for FRAME SIZE
// 4 bytes for STREAM_SIZE
// 4 bytes for VBR SCALE. a VBR quality indicator: 0=best 100=worst


And here

http://www.codeproject.com/Articles/8295/M...io-Frame-Header

it says

8, 12, 16, 108, 112 or 116 4 Quality indicator as Big-Endian DWORD
from 0 - best quality to 100 - worst quality (optional)

Strange.

Many thanks for your kind reply!
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