N2MP3 for Mac

From Proteron:

N2MP3 contains the Proteron MPEG encoder for MPEG1 layer III format. The algorithm is a variation of the psycho acoustic model and supports variable bitrate (VBR) with minimum bitrate specification and full support for joint stereo encoding. The quality of Proteron's encoder is of the highest caliber and is being licensed from Fraunhofer-Thomson. Although based on the International Standard source for MP3, the Proteron encoder includes proprietary improvements making it substantially better-sounding than plain ISO psy-model based encoders. On most G3 Macintosh computers, including all iMacs and iBooks, Proteron's MPEG Encoder is capable of encoding 128kbps, better quality (psy-model) MP3s faster than real time. Lower quality modes are much faster of course, and higher bitrates approach that of full-quality 44khz CD audio.