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Re: [Bug-gnupod] SoundCheck/ReplayGain


From: chris.com
Subject: Re: [Bug-gnupod] SoundCheck/ReplayGain
Date: Sat, 06 Jun 2009 10:10:16 +0200
User-agent: Thunderbird 2.0.0.21 (Windows/20090302)

This time I added the RG values (-9, -6, ...) to the mp3 files and told foobar to apply non-losslessly the RG to the files and I removes all the ReplayGain tags
I loaded the files in iTunes for it to add the SoundCheck data.
I noted the Volume correction iTunes applied for each song add came up with the following table:

file    rg      Volume  iTunesSD        (decimal)
------------------------------------------------------
m9      -9      +3.1    00 00 03        +3
m6      -6      +0.2    00 00 00        +0
m3      -3      -2.4    ff ff fe        -2
p0      +0      -5.0    ff ff fb        -5
p3      +3      -7.8    ff ff f8        -8
p45     +4.5    -9.3    ff ff f7        -9
p6      +6      -10.1   ff ff f6        -10
p75     +7.5    -10.8   ff ff f5        -11
p9      +9      -11.8   ff ff f5        -11

where
file:   m9 for -9, m6 for -6
rg:     the ReplayGain applied with foobar
Volume: Volume correction by iPod (Get Info function)
iTunesSD:
        The hexadecimal value found in the iTunes created iTunesSD file

All files sound (more or less) the same
The p75 and p9 files don't sound exactly the same because they get the same volume correction applied even though they don't have the same volume.

I only recovered the hexdumps of the iTunesSD that I join
If you want more information I'll redo the experiment

So, it seems than *ipod 2nd gen shuffle* uses the integer ReplayGain value with some crude rounding up algorithm. Rather crappy By the way, http://www.ipodlinux.org/wiki/ITunesDB#iTunesSD_file doesn't speak of a SoundCheck field but of a Volume field!
The range specified (0x00 - 0xC8) doesn't seem to correspond.

What do you think?
Cheers
        Chris

P.S. Do you happen to have an algorithm lying around that can convert the SoundCheck value to ReplayGain? I'm not that good at maths :(



H. Langos wrote:
Hi chris,

On Fri, May 29, 2009 at 12:36:30AM +0200, H. Langos wrote:
...
As you see the gnupod file allways contains 00 00 64 in the volume field while the iTunes generated field contains:
ff ff f7 for the -9dB file,
ff ff fb for the 0 file (are you sure it is realy 0? soundcheck 3E8 or none at 
all?),
00 00 09 for the +9dB

Unfortunately this is not the format documented in http://banshee-project.org/~gburt/itunesdb.html so we'll have to
investigate a little further.

Are you sure that the manual volume adjustment in iTunes was +/-0% for all
files?

It would be great if you could send me some more examples with +6dB and -6dB
and maybe +3dB and -3dB.

Did you get around to run those additional tests? If you did, please post
those to bug-gnupod.
cheers
-henrik



00000000  00 00 09 01 08 00 00 00  12 00 00 00 00 00 00 00  |................|
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00000230  00 00 00 00 00 00 00 00  00 00 00 00 00 01 00 00  |................|
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000002a0  00 65 00 64 00 5f 00 72  00 67 00 5f 00 6d 00 36  |.e.d._.r.g._.m.6|
000002b0  00 2e 00 6d 00 70 00 33  00 00 00 00 00 00 00 00  |...m.p.3........|
000002c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
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00000460  00 00 00 00 00 00 00 00  00 00 00 01 00 00 00 02  |................|
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*
00000af0  00 00 00 00 00 01 00 00  00 02 2e 5a a5 01 00 00  |...........Z....|
00000b00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
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00000b70  00 33 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |.3..............|
00000b80  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000d20  00 00 00 01 00 00 00 02  2e 5a a5 01 00 00 00 00  |.........Z......|
00000d30  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
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00000d60  00 2f 00 4d 00 75 00 73  00 69 00 63 00 2f 00 46  |./.M.u.s.i.c./.F|
00000d70  00 30 00 33 00 2f 00 67  00 30 00 5f 00 61 00 70  |.0.3./.g.0._.a.p|
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00000da0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000f50  00 01 00 00 00 02 2e 5a  a5 01 00 00 00 00 00 00  |.......Z........|
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00000fa0  00 31 00 2f 00 67 00 30  00 5f 00 61 00 70 00 70  |.1./.g.0._.a.p.p|
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00000fc0  00 70 00 37 00 35 00 2e  00 6d 00 70 00 33 00 00  |.p.7.5...m.p.3..|
00000fd0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00001170  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 01  |................|
00001180  00 00 00 02 2e 5a a5 01  00 00 00 00 00 00 00 00  |.....Z..........|
00001190  00 00 00 00 00 00 00 00  00 00 00 00 64 00 00 01  |............d...|
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000011d0  00 2f 00 67 00 30 00 5f  00 61 00 70 00 70 00 6c  |./.g.0._.a.p.p.l|
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000011f0  00 39 00 2e 00 6d 00 70  00 33 00 00 00 00 00 00  |.9...m.p.3......|
00001200  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
000013a0  00 00 00 00 00 00 00 00  00 00 00 00 00 01 00 00  |................|
000013b0
00000000  00 00 09 01 08 00 00 00  12 00 00 00 00 00 00 00  |................|
00000010  00 00 00 02 2e 5a a5 01  00 00 00 00 00 00 00 00  |.....Z..........|
00000020  00 00 00 00 00 00 00 00  00 00 00 00 03 00 00 01  |................|
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00000230  00 00 00 00 00 00 00 00  00 00 00 00 00 01 00 00  |................|
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00000690  00 00 00 00 00 00 00 00  00 01 00 00 00 02 2e 5a  |...............Z|
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*
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*
00000f50  00 01 00 00 00 02 2e 5a  a5 01 00 00 00 00 00 00  |.......Z........|
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00000fc0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00001170  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 01  |................|
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000011f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
000013a0  00 00 00 00 00 00 00 00  00 00 00 00 00 01 00 00  |................|
000013b0

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