Dithering is when you add noise to a recording so that when you lower the sample rate the result sounds more granulated. It tricks the ear into thinking that there is more information there then there really is and sounds a little more natural.

Vocoders apply the Sonic spectrum of one source to the equalization of another source. The result is very subtractive and tends to sound "pure" like a flute.

Sorry I'm so brief. Maybe my lack of detail will insight others to comment.