Only in the strange year of 1974 could the seemingly gleeful song lyrics, "Hey kids, rock and roll, rock on..." be delivered as a morose, melancholy plea. The effect was achieved not through irony, but through the literal sentiment that those words conveyed in that gloomy year. (1974 was, among other things, the year that President Nixon resigned, the year that inflation skyrocketed to 11 percent, and the year that overtly insecure books like I'm OK--You're OK topped the bestseller list.)

The heady 1960s were obviously long gone, and the disappointing reality of the crashed youth movement had, by 1974, infused rock music with melancholy. Indeed, the "movement," with rock music as its once-bold soundtrack, apparently hadn't accomplished much at all. The war in Vietnam didn't end as a dramatic statement of peace, but rather, it petered out long into the '70s, with 54,000 young Americans dead. Meanwhile, rock and roll values--sex, drugs, protest--had been co-opted by sickly suburban swinging parties, idiotic drug abuse, and weird cults like the Charlie Manson Family or the Symbionese Liberation Army.

With this deflated backdrop, not only did glitter star David Essex sing, "Hey kids, rock and roll, rock on..." as if he were asking people to throw themselves off the tallest building, but his song, with its equally melancholic and somewhat unintelligible rhythm, was in the Top 10 for five weeks, hovering in the Top 40 for 14 weeks.

I bring up this morbid song (it's a fantastic song, by the way) because for me it defines FM radio. I was eight years old in 1974, and FM radio was just shedding its underground status, blossoming into the mainstream, bringing with it oddities like "Rock On." Indeed, FM radio, as I discovered it through my older brother, was the strange new place where you heard Black Sabbath and Led Zeppelin--and late at night, terrified about what the older kids were possibly up to, you could hear David Essex's nightmare incantation (and bona fide hit).

By contrast, in the early 1960s, only about one-third of American homes had FM receivers, and less than five percent of cars had FM tuners. In those years, according to Len Christian, former senior vice president for radio at the National Association of Broadcasters, FM was obscure--something akin to today's college radio stations. "FM ran a lot of uninterrupted music because they were having trouble selling air time and there weren't a lot of commercials," Christian told the Orlando Sentinel Tribune. "They played a lot of classical music and string music, esoteric-type programming. There was a mixture of jazz and classics." FM also served as home to a nascent version of National Public Radio.

In the late '60s, wildly evolving rock music found a natural home in FM's experimental format, leaving the bubble-gum pop hits to the AM dial. This is where the term Album-Oriented Rock (AOR) comes from. FM radio featured "serious" album cuts as opposed to two-minute-and-50-second ditties. By the mid 1970s, through the growing popularity of FM, those album cuts would become the hits and go on to replace AM. By way of example, in 1975, 61 percent of the nation's radio audience tuned to the AM dial; today that percentage has dropped to less than 20 percent.

FM, which stands for frequency modulation, has officially been around since January 1941 when the FCC approved its commercial use. The technology itself had been around since 1933-34, when its inventor, Edwin Armstrong, demonstrated his radio wizardry to RCA. In June of 1934 he began broadcasting from the Empire State Building, and in 1939 he started what's widely credited as the first FM radio station, W2XMN in New Jersey.

Armstrong's invention was to AM what color TV was to black-and-white television. FM reduced the extraneous noise and errant signals that plagued AM by varying the number of radio waves per second, as opposed to AM technology, which varied the power of the radio wave. Basically, Armstrong dealt with the shape of the wave, not its power, which allowed FM broadcasts to adapt to sound variations. This made FM quality far superior to AM, which had been around since 1920, relying on talk and drama formats that weren't as sonically demanding.

Unfortunately for Armstrong, who had hoped that his patent would bring him millions through a deal with the General Electric company to build FM receivers, WWII came along and occupied GE's time and money.

After the war, feeling threatened by the potential of FM broadcasts, AM radio companies like RCA bought up the FM licenses and simply began simulcasting their AM broadcasts on FM. Since there was nothing new on the FM dial, the medium didn't blossom, and listeners just stayed tuned to AM where music didn't sound as good. Adding to its irrelevance, the FCC relegated FM to its own, apparently secret, bandwidth: 88 mhz--108 mhz.

In the 1950s, the number of FM stations numbered only about 500. Still, Armstrong wanted to profit from the use of his invention. However, RCA, which was interested in FM technology for TV use, battled Armstrong in court and stole his invention, winning the right to use FM on its own terms. In 1954, the frustrated inventor committed suicide by jumping out the window of his New York apartment. Armstrong was 65 and living in poverty.

Over the next decade, a few key developments would avenge Armstrong's demise. First, in the mid-1950s, companies started developing FM receivers for cars. (This trend exploded in the mid '60s.) Second, in the early 1960s, FM started broadcasting in stereo. Third, the government started regulating AM/FM simulcasts, freeing up FM radio up to create alternatives in earnest.

However, Armstrong's revenge (FM's rise to dominance) wasn't truly set in motion until the mid- to late '60s, when rock music became FM's secret weapon. As rock music took control of the record industry, FM served as its outlet. While the passé sound of the older generation droned on AM, the hip sounds of album rock were wailing on FM. Nothing defined the potent "generation gap" of the late '60s and early '70s more than the AM/FM split. AM listeners voted for Nixon. FM listeners voted for McGovern.

Sadly, by the late 1970s and early '80s, as rock experimentation gave way to the prefabricated "experimentation" of Kansas and Boston, FM radio became a commercial wasteland. FM turned into a parody of itself, with "art rock" hit singles simply taking the place of bubble-gum AM radio pap. Thankfully, there was punk. In the late '70s and early '80s, punk secretly served the same function that rock music had served in the late '60s. Slivers of the FM airwaves were colonized by college and punk stations that kept the original FM spirit alive up through the '90s. Sort of.

However, the golden age of FM was surely the early 1970s, when FM radio was powerful enough to create hits like David Essex's "Rock On," but close enough to its roots to remain experimental, capable of seducing people's younger brothers late into the night.