[vorbis-dev] Normalization of ogg vorbis file / tweaking the floor ...

[Sebastian Gesemann]

On Mon, 2 Jun 2003, John Morton wrote:

> > [...] without full reencoding
> > (Ogg Vorbis->PCM->Ogg Vorbis) of the file?
> Use replaygain[1], or specifically vorbisgain[2]. It will calculate gain 
> [...]
> This is what people usually want when they say 'normalization'. AFAIK, you 
> can't easily tinker with the vorbis frames to add a scale factor in the same
> way you can with MP3, but I could be wrong.

It depends on the floor type....
floor type 0 -> no way
floor type 1 -> conditional
Today's Ogg/Vorbis files use floor type 1

It's possible to tweak the floor's offset by altering the (directly 
(not using a code book) encoded) first two Y-coords of the floor.
But it can happen, that the other Y-coords are decoded incorreclty
then, because of the modified [low_room] and [high_room].
In those cases it's still possible to just reencode the whole floor with
an other offset.

In either way... you won't loose quality, but you can only adjust the
vomlume by +/- 2.2 dB for currently encoded vorbis files...
(the multiplier for 'short' floors is 4 -> 140dB/256*4 ~= 2.2 dB)
which is not very fine... so... the only way to fine-tune the gain is
using the vorbis-gain-comment-tag.

<p>BTW: My from-scratch-vorbis decoder is working now. HORAY! :-)
(except for floor type 0 - i've implemented it, but it does not
work atm)

<p>bye,
Sebastian

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