[flac-dev] R128gain & metaflac

[Ian Nartowicz]

>The use of R128 also raises the question about "REPLAYGAIN_REFERENCE_LOUDNESS"
>tag. Currently flac/metaflac writes "REPLAYGAIN_REFERENCE_LOUDNESS=89.0 dB"
>but doesn't use it when decoding (it seems that nothing uses this tag).
>R128 defines reference level differently, so this tag makes little sense for
>it. IMHO it's better not to write this tag when (meta)flac uses R128 algorithm.
>
I use it :)  To optionally allow adjustment of tracks containing different
types of gain tag to a similar overall loudness.  Admittedly this isn't
common.  Files using the original replaygain algorithm with a reference
loudness of 83dB are now very rare, but R128 tags are starting to show up
(eg. in Opus) and these play at a significantly different (quieter) level to
tracks adjusted with the 89dB reference loudness tags.  However the volume
changes between the two different tagging systems are so dramatic that it is
helpful to provide an automatic method of normalising them at least
approximately.

While adding the option for R128 gain into metaflac (and/or flac) would
certainly be useful, I consider that scheme to be poorly suited to music
playback.  I certainly wouldn't want it to be imposed, or even the default.  As
the original, and still far more widespread, replaygain quickly discovered
using a gain specification designed for movies leaves far too much headroom and
hence is too quiet for music, far too quiet for standard commercial rock and pop
recordings.  R128 is even slightly worse in this respect, being more than 6dB
(nominally 9dB, but possibly closer to 6dB in practice) quieter than
replaygain.  What that means is around 8 of the 16 bits in a typical music
recording are unused, and I suspect most people would (rightly or wrongly) be
horrified if you told them all their music was suddenly 8 bits. Turning up the
volume cannot correct for that, although applying a preamp gain could.

Music players that have adopted R128 or are planning it have often adjusted it
by several dB to avoid the "too quiet" issue.  With no standard in place
concerning this and R128 itself being revised it isn't at all clear just what
metaflac should do.  Personally I think it would be better for players to
automatically apply a preamp gain on top of R128 replay gain tags, but unless
and until that is widely adopted, it would be unwise for encoders to reply on
it.

>The use of R128 also raises the question about "REPLAYGAIN_REFERENCE_LOUDNESS"
>tag. Currently flac/metaflac writes "REPLAYGAIN_REFERENCE_LOUDNESS=89.0 dB"
>but doesn't use it when decoding (it seems that nothing uses this tag).
>R128 defines reference level differently, so this tag makes little sense for
>it. IMHO it's better not to write this tag when (meta)flac uses R128 algorithm.
>
>(David Robinson, the author of ReplayGain, thinks that such tags are useless:
It's useless only because nobody uses it :)  To be honest there is very little
need for it today.  99%+ of replaygain tags use the newer 89dB reference and
99%+ of players expect that (at least in their latest versions), so specifying
the reference loudness really is useless except for a minuscule minority of
situations, and almost certainly the players in those situations don't do
anything with the tag anyway.  So the only real purpose of the tag would be if
it said something other than 89dB.  I still parse it, if present, because it
does no harm.

--ian