Don Pearce wrote:
On Mon, 10 Jul 2006 11:10:55 GMT, "dadiOH"
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.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."