COMM - iTunes Normalization Settings (class 3)

iTunes writes a standard comment with a description of iTunNORM. This contains the normalization information it uses. A sample is:

• 00001E86 00001E86 0000A2A3 0000A2A3 000006A6 000006A6 000078FA 000078FA 00000211 00000211

Discussions on the values:

• http://robinbowes.com/projects/flac2mp3/ticket/30

• http://www.hydrogenaudio.org/forums/index.php?showtopic=24620 (with code at http://studwww.ugent.be/~jdebock/ipod/ipodrg.cpp)

• http://svn.slimdevices.com/trunk/server/Slim/Utils/SoundCheck.pm?rev=10330&view=markup which says:

  The iTunNORM tag consists of 5 value pairs. These 10 values are encoded as
  ASCII Hex values of 8 characters each inside the tag (plus a space as prefix).
   
  The tag can be found in MP3, AIFF, AAC and Apple Lossless files.
   
  The relevant information is what is encoded in these 5 value pairs. The first
  value of each pair is for the left audio channel, the second value of each
  pair is for the right channel.
   
  0/1: Volume adjustment in milliWatt/dBm
  2/3: Same as 0/1, but not based on 1/1000 Watt but 1/2500 Watt
  4/5: Not sure, but always the same values for songs that only differs in volume - so maybe some statistical values.
  6/7: The peak value (maximum sample) as absolute (positive) value; therefore up to 32768 (for songs using 16-Bit samples).
  8/9: Not sure, same as for 4/5: same values for songs that only differs in volume.
  iTunes is choosing the maximum value of the both first pairs (of the first 4 values) to adjust the whole song.