During the late '70s and early '80s, a crop of British experimentalists emerged with positions on conventional rock music that ranged from indifferent to hostile. Prompted by early electronic music and the advancements made by the BBC Radiophonic Workshop, Tangerine Dream, Kraftwerk, and Throbbing Gristle -- and eventually their peers -- they plied their trade on equipment with names like EMS Synthi A, EDP Wasp, Korg MS-10, and ARP Odyssey. For many of them, guitars and drum kits were obsolete. Synthesizers, drum machines, and tape delay units, many of them shrinking in size and cost, were the present and future way to sculpt jerking noises or strange pop songs. The fledgling musicians could record in bedrooms and release the results on cassette, or they could ally with independent labels and operate at studios like Blackwing, a haven for Mute and 4AD artists such as Depeche Mode and Cocteau Twins. Released by Cherry Red, one of those original outlets for music of the margins, Close to the Noise Floor: Formative UK Electronica 1975-1984 collects four discs of the alternately thrilling, grim, silly, and just plain bizarre stuff. Some of the groups, such as Blancmange, the Human League, and Orchestral Manoeuvres in the Dark, went commercial after they released their selected inclusions, while the likes of Wire's Bruce Gilbert and Graham Lewis appear here with a divergence into sound manipulation that resembles animal calls. Some of these tracks have appeared on widely available albums and compilations. The making of this set must have been an arduous undertaking, however, as the majority of the tracks were originally issued on cassettes and 7" vinyl in small quantities, previously heard by few sets of ears. Among the highlights of the accidentally obtainable and deliberately obscure: Thomas Leer's spangly narrative "Tight as a Drum," Adrian Smith's skeletal and crepuscular "Joe Goes to New York," and British Standard Unit's mutilation of Rod Stewart's "Da Ya Think I'm Sexy?" There's also Gerry & the Holograms' delightful self-titled theme song, placed on high rotation by temporary WPIX DJ Frank Zappa. The Mute massive -- Cabaret Voltaire, Robert Rental, and so forth -- are surprisingly absent, though they're represented somewhat by Alan Burnham's "Music to Save the World By," produced by label boss Daniel Miller (aka the Normal, the Silicon Teens). Given that so much scarce material is discerningly compiled here, it's hard to gripe about it and other exclusions. A great essay and a fair portion of the track-by-track notes come from Dave Henderson, who documented the global post-punk electronic underground as it developed, after being lured by "reading dismissive reviews in the weekly music press." Henderson's own group, Worldbackwards, contribute a glum but enchanting ballad that drones and stirs, then fades out to a bit of Sylvia Plath's "Lazy Lazarus." Henderson's assessment? "Man, we were pretentious."