It came about, for the most part, from 60s FCC
rules limiting the time an AM station could simulcast on its experimental FM signal. Since FM wasn't a Cash Cow (only audiophile
s, at first, had receivers), DJs could play anything
. Stations like San Francisco
's KSAN-FM and New York
's WOR-FM played LP cuts by underground
bands - an alternative to the poploop of Top 40
, and a means (alongside zine
s and underground newspaper
s) to wider exposure for The Dead
, et al.
It inspired the launch of a slew of "groovy, man" imitators across the US - KSAN is lauded as the "first freeform station", but it was really only the first high-profile commercial freeform station; founder Tom Donahue moved on, planting new stations elsewhere... upheavals caused some WOR jocks to move to the imitator-upstarts WNEW-FM and WABC-FM...
Success quickly led to a homogenization into rote format - "album rock" (AOR), and its progeny. There were some interesting experiments in TV simulcasts of concerts (stereo TV! groovy!), and experiments in quadraphonic sound (some US FM stations with "Q" in their call letters were part of this early-70s trend). Much college radio now is free-ish; WFMU (and KFJC) is the Real Deal. "Commercial freeform" has become an oxymoron. A pity.