The "Second Edition" is the first Dark Horse edition in hardcover, while the "First Edition" is the 1992 softcover release. There was a first edition hardcover published in the UK by VG Graphics/Victor Gollancz Graphic Novels.
Originally serialized in The Face (1980) Vol. 2, #9-15. Additional material was added, and revisions were made for the collected edition.
Soliciation copy: "Serialized in The Face in 1989, expanded and revised into a graphic novel in 1992, and adapted for radio in 2000, Signal to Noise has never stopped evolving. The bonus material in this first-time hardcover edition captures every leg of the journey, including three related short stories unseen in nearly two decades, an additional chapter created for the CD release of the radio drama, and a new introduction by Dave McKean along with the original by Jonathan Carrol and the radio drama introduction by Neil Gaiman."