Shorten (aka SHN) is a file format used to losslessly compress CD-quality audio files (44.1 kHz 16-bit stereo WAV). It is like ZIP/RAR/Stuffit but for audio (those compressors do not work well on audio data). This compression saves disk space and decreases transfer times.

WHY USE SHORTEN?
One of the primary goals of etree.org is to preserve the quality of original concert recordings. To that end, it's important that any compression used be lossless. When uncompressed, a lossless-compressed file is bit-for-bit identical to the original audio file. It's the exact same high quality as what the taper originally "seeded".

Lossy compression schemes are the opposite of lossless. The MP3 format is one such example. Lossy means that parts of the original recording are thrown out as the compressor does its business. The lower the bit-rate of the MP3 file, the more data is thrown out. This results in very small file sizes, but that lost data is gone forever. You can hear this clearly if you listen to low bit-rate MP3 files on a decent set of headphones or stereo system.

The danger of trading mp3's is that, like high-generation cassettes, the sound quality rapidly declines. When you burn a mp3 to CD, give it to someone else, and they rip it to mp3 again, their mp3's are a lot "emptier" than yours. Remember, more and more music data is squeezed out with each mp3 conversion. Do this a few times, and you end up with very poor sounding music.

Lossless compression schemes (like Shorten or FLAC) don't have this problem. The music is always exactly the same as the original, and you can be sure the music won't degrade into white noise a few trades down the line.

If you trade only mp3 files, never converting them to wav or CD and back again, you won't suffer this multi-generataional loss. The problem with this is you can't rely on others with whom you trade to do the same thing. The tempation is always there to burn the mp3's to CD. Once that's done, it's easy to rip mp3's, and the vicious circle starts again. However now that portable mp3 players have become popular, it is no longer necessary to convert mp3's to wav's in order to listen to them.

Moral of the story: stick with lossless encoding for trading!

The Shorten algorithm and the reference code that implement it were developed by Tony Robinson of [SoftSound Ltd.]. The code was made available under a generous non-commercial license and has been extended by Wayne Steilau to include seek tables so that you can seek within individual tracks when playing the files on your computer (e.g. with WinAmp, xmms, [foobar2000], etc).

Be sure to read and bookmark the [Shorten and MD5 FAQ] - it's a good starting point for all shn and md5 related questions.