Having seemingly failed to persuade the digital music world to upgrade to MP3 Pro, the format's founder, Germany's Fraunhofer Institute, is trying again, this time with MP3 Surround, a multi-channel implementation of the hugely popular music codec.

Its latest teasers are MP3 SX - short for 'stereo extended' - and Ensonido, respectively technologies for making stereo recordings sound better in a surround sound environment and down-mixing multi-channel sound into two-channel stereo.

The latter technique will be familiar to owners of DVD players that can dynamically mix a movie's 5.1-channel sound track into two channels. MP3 SX's trick isn't entirely new either, but the Fraunhofer Institute reckons its system is particularly good at converting a stereo 'image' into a multi-speaker set-up, avoiding common gotchas such as vocal and solo-instrumental sound sources appearing to come from odd locations.

MP3 SX and Ensonido are available now among Fraunhofer's MP3 Surround demo software selection, written to show what the format is capable of in the hope that audio companies will license the technology. The tools run on Windows, Mac OS X and, in the case of the Institute's command-line tools, on 32/64-bit Linux too.

MP3 Surround was launched just over a year ago, bringing 5.1-channel audio to the MP3 format. It's backward-compatible, so existing MP3 players can reproduce the content, albeit using only two of the channels. MP3 Surround builds on MP3 Pro, launched in 2001, which improved the format's encoding algorithms to generate smaller files with no further reduction in audio fidelity than the MP3 format already produces.

The software is available free of charge "for personal and non-commercial purposes" at www.all4mp3.com. ®