mp3quality encoder setting

[mikek401]

Has anyone experimented with the mp3quality encoder setting? Do you hear any difference in sound when using mp3quality=1 vs mp3quality=0?

The SHOUTcast DNAS Transcoder 2 documentation says:

mp3quality : Specify the MP3 encoder quality to use when encoding [Default = 0] Available options are :

0 - fast (preferred)
1 - high quality (changes sample rate and does additional filtering)

Does anyone know what it does with the sample rate? 'changes' to what?
What filtering is performed?
Why is 0 'preferred'?