Spectral contains a large wedge of graphics and sonics converted from a number of demos on the Sinclair Spectrum. The original idea for this demo pretty much came about from the "annual" comp.sys.cbm and comp.sys.sinclair flamewar, where wilder and wilder claims get made about what the C64 and Spectrum can and can't do.
The multiplex part (in the screenshot) was originally written to prove a point regarding hardware versus software sprites and was expanded on later; originally the plex ran over a conversion of the Speccy version of Wizball's loading picture and the final scroller had a different picture again when it was originally coded.
Review: "Spectral is an insight into world of speccy demos for c64 people. it contains converted speccy graphics along with remakes of famous and not so famous speccy chiptunes. its well linked and goes on good way, the graphics are converted very well, so... all in all it is nice. as an insight ofcourse - if it was a pure c64 demo i would like it just because music!"
Raver/Phantasy (from Pouet.net)
Trivia: hold down the Commodore key during the decrunch until the screen wipe starts to get into the hidden part.