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://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.