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Posted by Eeyore on 10/16/83 11:52
Scott Dorsey wrote:
> Don Pearce <nospam@nospam.com> wrote:
> >On Mon, 10 Jul 2006 11:10:55 GMT, "dadiOH" <dadiOH@guesswhere.com>
> >wrote:
> >
> >>David Morgan (MAMS) wrote:
> >>
> >>> I had a look, and I can't see how the device works without modifying
> >>> dynamic range
> >>
> >>Simply put...
> >>
> >>1. Find max volume among all songs
> >>2. "Turn up the volume" in all others so their max is the same as the
> >>loudest.
> >
> >Won't work - can't work. If you have a mixture of music, then peak
> >levels as related to average loudness will vary wildly. The loudest
> >sounding will have highly compressed dynamics, with most of the tune
> >crammed against the limit. If you try to increase the levels of all
> >the others until they sound as loud, they will all be clipped to hell.
>
> What you're forgetting here is that the MP3 is not just PCM data with
> absolute scalar values for every sample. There is a "volume" field in
> the header which tells the playback application how loud to play the
> thing. By tweaking THAT, you can turn down the level of a track without
> affecting the actual resolution (except of course the resolution is still
> limited by the converters at the final playback, and if the gain is lowered
> digitally, that will be reduced... still, that's a marginal problem at
> best).
>
> The thing is, that field is ALWAYS maxed out whenever anyone hands you
> an MP3, because all the encoders want their products to play back as loudly
> as possible. So you can usually turn it down, but seldom can you turn it
> up.
That's interesting Scott.
Is there a handy application to edit the header ?
Graham
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