Trixter, digital P.I. and archaeologist, has been tracking down authors who long ago reverse engineered custom audio formats. He stalked down one Adrienne Cousins, the author of a program called Sputter, a multi-format audio file encoder/decoder… all in 16-bit x86 ASM! The source includes codecs for the Covox ADPCM formats mentioned recently. Thanks to Kostya, though, for independently reverse engineering and documenting the format.
Still, there might be some other gems in the Sputter source code. The author has granted permission to redistribute the source, and it is now in this directory: http://samples.mplayerhq.hu/A-codecs/CreativeADPCM8bit/. Also in that directory is a package called VEDIT.rar which contains an old EGA-based program that is able to encode VOC files to that arcane 2.6-bit ADPCM format that the Sound Blaster could encode and decode in hardware. If reversed engineered, it might describe how the 2.6-bit algorithm works.
What I’ve been looking for for several years, off and on, is Sputter Sound system 1.15, mainly for the collection of audio files that came with it.
All I’ve been able to find are text files listing long gone FTP and BBS sites where it (and so many other old programs) used to be many years ago.
What doesn’t help is that if any of those archives still exist, they have robots.txt files and many search engines will not index a site at all when they find that, even if there’s sections the robots file specifically allows to be indexed.