I've heard about De-emphasis on MP3/2 streams.

Three kinds of de-emphasis I found references of:

-None
-50/15 ms
-CCITT j.17

I'd like to know what it is, and if they can affect encoding quality in any way.

Thanks for any help.

Regards;

Roberto.

Pre-emphasis/de-emphasis is a technique used in all sorts of
communication channels to give better overall signal to noise ratio.
Basically the frequency response of the channel is weighted
(typically with a 6 dB/octave slope) prior to transmission, and then
the inverse of this weighting is applied at the receiving end to
restore a flat frequency response.

So it's just a complementary pair of filters...