Winamp 2.9x and 5.x EQ.
To anyone using the EQ in Winamp 2.9x or 5.x (does not apply to 3.x or 2.8x and earlier)
2.9x introduced new EQ code by 4FrontTech. This new EQ is said to be much better than the original Nullsoft EQ.
But for whatever reason, Nullsoft has the new 4Front EQ disabled by default for the Mpeg Decoder plugin (which handles all mpeg formats and AAC) All other plugins like WAV, Ogg, MOD, etc.. use the new EQ!
To enable the new EQ for the MPEG decoder bring up the Properties screen for the Mpeg Decoder plugin, on the Decoder tab disable the "Fast Layer 3 EQ" option. Disabling this option causes the new EQ code to be used. The setting takes effect on playback. You should definately notice a difference. To me it sounds much better. (I use the Full Bass and Treble preset)