Trixter, who’s interested in even older multimedia formats than I am, has unearthed utilities to compress special ADPCM variants used by the Covox Sound Master. The formats include 2-, 3- and 4-bit ADPCM formats. For anyone interested in trying to reverse engineer the details of these obscure formats (and I know you’re out there), check out this directory at the samples site. It has PCM samples compressed in the various formats along with the DOS-based compression utility used. Also, there is a programming library that has C code to interface to a binary library module that handles the meat of the codec operations.
Happy RE’ing.
oldskool.org appears to be a broken link.
Yes, that’s because http://www.oldskool.org is the site, not just the domain.
Fixed, thanks. I thought I tested the www-less address when I posted it.
A quick look shows that this is not ordinary ADPCM, as it has markers inside:
FF 55 FF AA FF 55 FF AA – header (compression type follows)
FF 55 55 55 – some marker (block start?)
FF AA AA AA – EOF
I’ll look further into it when I have some time (sigh)