[vorbis-dev] Re: [vorbis] Amplify Ogg files without decode/encode

[Segher Boessenkool]

Mike Coleman wrote:
> 
> xiphmont at xiph.org (Monty) writes:
> > Floor 0 has a master amplitude value encoded in dB.  Just adjust it
> > per packet per channel.
> 
> I thought something like this existed, even though I wasn't seeing it in the
> code.  Is this sufficient by itself?  I was worrying that the residues also
> needed to be scaled.
> 

Well, if you do it this way, you'll need to cahnge "amp" (and possibly
"ampdB", if
scaling up) _per block_, so you'll need to reencode every block, and
you'll need to
be very careful that every block gets scaled up (or down) by very
exactly the same
value, as otherwise you will certainly hear it, esp. in the bass
frequencies (it'll
generate artificial overtones, somewhat like the well-known mp3 blips).

If, on the other hand, you scale the residue values, you'll only need to
do it in the
codebook headers, and you don't need to worry too much about precision,
as every block
will get scaled by the exact same factor.

Dagdag,

Segher

--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/
To unsubscribe from this list, send a message to 'vorbis-dev-request at xiph.org'
containing only the word 'unsubscribe' in the body.  No subject is needed.
Unsubscribe messages sent to the list will be ignored/filtered.