>
> Hi folks,
>
> One of the utilities, namely mp3amp.exe, available
> at http://www.chat.ru/~lrsp/coding.html (thanks to
> Sergey) made me curious about this "normalization"
> issue once again ...
>
> Can anyone please explain it to me in more details,
> or/and point to some references ??? Here is what
> Mark said earlier (and, I guess, what Sergey's
> utility does):
>
> > One easy thing would be to change the value of
> > global_gain. it's an 8bit int stored for each
> > channel of each granule. Changing this +/-1
> > changes the volume by .75db.
>
> But volume of *what* does this value change ??? To
> what value global_gain is set during encoding ???
> Most likely, it is set according to some mean
> level of the source data; and then it tells to
> decoder with what factor to amplify frame content.
> If so, how the result of such decoding will differ
> from regular normalization ???
>
> Now I'm totally confused: what is "regular
> normalization" anyway ??? Isn't it multiplying
> data to some constant factor ???
>
> Any help would be appreciated.
>
the mp3 global_gain is just a scaling, applied in each frame, to get
the MDCT coefficieints to range from 0 and 8192 before quantization.
When decoding, the data has to be unscaled by the same amount to
restore it to the original volume. If you change this value in the mp3
file, then you are chaning the amount of "unscaling" and the
output will be proportionally louder.
Mark
--
MP3 ENCODER mailing list ( http://geek.rcc.se/mp3encoder/ )
