Below-bit-level encoding

[Dale Thorn]

Does anyone have info or know of a text source on less-than-bit-level 
file preparation?  I presume the crypto techniques would be the usual 
stuff; I'd like to dig into bit deconstruction a little, and a text 
which has a chapter or more devoted to this and other esoteric file 
processing would be helpful.  Note that this is not substitution or 
bit-packing or whatever.  Thanx.