Lossless Predictive Audio Compression

(LPAC) A lossless audio compression algorithm with compression ratios from 1.5 to 4, depending on the input. Software is available for Microsoft Windows, Linux and Solaris. LPAC files (*.pac) can be played with a Winamp plug-in.

http://www-ft.ee.tu-berlin.de/~liebchen/lpac.html.