ReplayGain2

Writing ReplayGain track and album gain tags with an intentionally different reference loudness is a very bad idea. It breaks existing players.

It is fine to use a new calculation method with a new reference loudness, but the values must be converted to the original reference loudness before being written to ReplayGain tags. That way, loudness matching will work on all ReplayGain compatible players across all ReplayGain tagged files.

An extra tag can be used to tell new players how to convert back to the new calculations' reference level if required, without breaking compatibility with old players. That way, you get the best of all worlds.

Consider an album with a loudness of -17 LUFs containing a track with a loudness of -16 LUFs
Assuming the 5dB conversion is used (i.e. assuming -23LUFs is 5dB quieter than the (83+6)dB SPL reference of ReplayGain), then...

This is good...
REPLAYGAIN_TRACK_GAIN=-2.0 dB
REPLAYGAIN_TRACK_PEAK=1.0000
REPLAYGAIN_ALBUM_GAIN=-1.0 dB
REPLAYGAIN_ALBUM_PEAK=1.0000
REPLAYGAIN_ALGORITHM = EBU R128
REPLAYGAIN_CONVERT_TAG_VALUES_BACK_TO_THAT_ALGORITHM = -5 dB
(might need to think of a better name for that tag )

While this is bad...
REPLAYGAIN_TRACK_GAIN=-7.0 dB
REPLAYGAIN_TRACK_PEAK=1.21822226
REPLAYGAIN_ALBUM_GAIN=-6.0 dB
REPLAYGAIN_ALBUM_PEAK=1.21822226
REPLAYGAIN_ALGORITHM = EBU R128
REPLAYGAIN_REFERENCE_LOUDNESS = -23.00 LUFS


The idea is that existing players should work as they always have, while new players have the option of doing something different.

If you write track and album tags to a new reference level, but only mention that new reference level in a new tag which existing players ignore, you prevent all existing players from using those ReplayGain tags to match loudness. This is a bad thing.

Cheers,
David.

P.S.
EBU R128 GAIN = REPLAYGAIN_TRACK_GAIN + REPLAYGAIN_CONVERT_TAG_VALUES_BACK_TO_THAT_ALGORITHM
EBU R128 loudness = -23 -(REPLAYGAIN_TRACK_GAIN + REPLAYGAIN_CONVERT_TAG_VALUES_BACK_TO_THAT_ALGORITHM)