PlusV is a brand new audio compression enhancement technology that allows audio files to be compressed in as little as 64 or even 48 kbits/s. PlusV is not a compression scheme of its own, it is an extension that can be applied to existing audio formats. When combined with the MP3 technology, MP3+V files are fully compatible with existing MP3 files and decoders. To get full audio quality out of PlusV files, you just need a PlusV capable decoder, like a PlusV capable WinAmp plugin.

http://www.plusv.org/