"While they could tell me it was dangerous to walk through this neighborhood or that neighborhood, no one could tell it was dangerous to listen to this particular music," said Ramsey, a professor of music at the University of Pennsylvania. "Music widened my social and cultural outlook and gave me a way to understand people different from myself."

While fault lines were opened by racial tensions, gender gaps and the Vietnam War in 1968, it was through music that people often, and sometimes unexpectedly, found themselves on the same solid ground.

"There was a sense that the music of different cultures and communities could be brought together," said Graeme M. Boone, professor of music at Ohio State University. "It was tremendously liberating."

Ramsey, author of "Race Music: Black Cultures from Bebop to Hip-Hop," says the flow of black music into the mainstream of popular culture increased white sympathies for the civil-rights movement.

"Beginning in the 1940s, the popularity of black popular music exploded because of shifting demographics [black Southerners migrating to Northern cities]," Ramsey said. "Coupled with a proliferation of independent record labels that sought out new forms of music and entertainers, the scene was ripe for mass-mediated black images.

"This continued into the 1960s. Together with the sudden appearance of civil-rights-era images of marches, protests, dogs barking at and fire hoses trained on black citizens, a moral authority began to shift toward African-Americans."

It was into this milieu that Motown appeared: Berry Gordy's assembly line of pop songs with infectious beats, glamorous images, succinct and catchy lyrics and precise musical arrangements.

"Gordy and all he symbolized did much to open up a space for Americans to think that civil rights for all was a perfectly reasonable goal for which to strive," Ramsey said.

More barriers fell as artists like The Doors, Jimi Hendrix, Sly and the Family Stone and the Beatles (who had the year's No. 1 hit with "Hey Jude") defied distinctions by absorbing a wide range of influences.

Someone like Janis Joplin, for example, transcended her image as a white female and embraced the legacy of the great, black blues songstresses of the 1920s, Ramsey said.

The Temptations, on the other hand, moved away from traditional love songs like "I Wish It Would Rain," which were "part and parcel of black popular music," to songs of social change, like "Ball of Confusion."

Not only did musicians reflect and affect social changes, they also took on the politics of the Vietnam War.

"Wars always affect music because wars affect culture profoundly," Boone said. "It was during World War I that jazz burst on the scene; during World War II bop came out and during the Vietnam War rock emerged.

"The war was a tremendously powerful motor towards the idea that rebellion was necessary."

The 1950s is often seen as the era of a "rebel without a cause;" the 1960s can be viewed as the era of "a rebel with a cause," Boone said.

"This music suggests a moment, historically, where the counter-culture became the culture," he said. "But by the '70s, when you see construction workers growing their hair out and wearing bell bottoms, you knew it was over. They were the same people that beat up the hippies in the '60s."

The "let's change the world" idealism of the mid-'60s, had deteriorated by 1968, and when Martin Luther King Jr. and Robert F. Kennedy were killed that year, something in the music died too, said Harvey Holiday, a Philadelphia disc jockey of more than three decades.

"I think the hope of Dr. King and Kennedy was more prevalent in music when they were alive," he said. "A lot of people thought their assassinations were the death of hope. The spunk was taken out of the youth movement because their heroes were taken down."

In Philadelphia, people were getting their music on TV from "The Ed Sullivan Show" on Sunday nights and on the radio from WDAS, one of the nation's first African-American radio stations, which hosted leaders like King and Malcolm X, Holiday said.

It was also the year that the Intruders gave birth to the "Philly sound" with their hit, "Cowboys to Girls," he said.

At the time, radio was a major influence on people like Holiday, who fell in love with music by listening in bed at night to the AM channels.

On the FM dial, radio was charting new ground by playing 20-minute songs from concept albums and promoting the idea of "listening environment," Boone said.

In 2008, when music is bought not from a store but from a Web site, and is listened to not on radio but on-demand, it's hard to get the sense of convergence that the music of the late 1960s produced.

This year, though, the music of 1968 and 2008 converged when Wayne Kramer, founder of rock pioneers MC5 (Motor City Five), the only band to play at the volatile 1968 Democratic National Convention, performed with Rage Against the Machine during the "Tent State Music Festival to End the War" at this year's DNC.

"People say the golden age was over by 1968," Boone said, "but that all depends on who is writing the history." *