Dissent sometimes comes with a soundtrack.

As protest marches fill streets in cities across the country, participants are putting their concerns to song and, increasingly, to percussive chants.

It's part of a long tradition of songs sung in protest against racial discrimination, wars, union busting, hippie culture, social injustices — even against protests.

Americans long have cast their emotions in musical form, said Alex Lubet, a professor of music and adjunct professor of American studies at the University of Minnesota.

"Scientists have tried to determine why music is so universal, and not one has come up with a single answer," he said. "It's a basic human need. So it's only natural that people use it in protest. Yelling louder can be ­effective, but it's the addition of aesthetics — of putting words to a melody — that creates something that may last."

There's no particular format for a protest song, said Lubet, 61. Some are pointedly about a single topic, while others address the broader human condition.

Of the latter, look to Bob Dylan, a son of Minnesota's Iron Range, who wrote some of the most durable protest songs, notably "Blowin' in the Wind" and "Masters of War." Oh, and "The Times They Are A-Changin.' " Oh, and "A Hard Rain's A-Gonna Fall."

"Dylan's approach was the most mythological and almost oblique," said Brian Laidlaw, 33, a folk musician recently of Minneapolis, now of Denver, who occasionally teaches classes about writing protest songs.

"Blowin' in the Wind" endures, he said, because its message of being responsive to suffering can apply to so many episodes in history.

Some, of course, prefer fire over subtlety, Laidlaw said. "Ohio," about four students killed at Kent State in 1970 when National Guardsmen began firing at an antiwar protest, is such an anthem.

"It can feel good to write a song that's really cathartic, you know, 'What are all you idiots doing?' " he said. "But if you truly want to effect change, that can't be your thesis statement. Dylan realized this. His use of lyric is so subtle, so glacial."

A three-legged stool

So what goes into a good protest song?

Laidlaw has an MFA in poetry from the University of Minnesota, taught songwriting at McNally Smith College of Music in St. Paul and is in a Ph.D. program at the University of Denver. He regards the protest song as "the ideal form to practice rhetoric as a songwriter."

But just as in an effective essay, he said, a protest song depends on three legs: "It's a strong performance about an urgent topic with a specific audience in mind." Too often, he said, protest songwriters do only two out of three well, and the missing component results in a wobbly effort.

Who sings protest songs?

The usual suspects are considered left-wing, liberal, socialist, unionist, revolutionary, anti-whatever. But those deemed right-wing, conservative, establishment, pro-whatever also can come up with memorable anthems.

Merle Haggard's "Okie From Muskogee" often comes to mind, written in 1969 when Haggard had grown disheartened watching Vietnam War protests. It twanged against drug use, draft dodging and the counterculture in general, and went on to be named song of the year by the Country Music Association.

Likewise, Barry Sadler's "Ballad of the Green Berets" of 1966 protested the protests against the Vietnam War, supporting government policy and the troops. It was named Billboard's No. 1 single for the year.

If there are fewer such hits now, it may spring from a period of relative calm — although controversial police shootings of black men have inspired new artful protest. But there also are so many more pathways for songs to reach a specific audience, diffusing their ability to sweep the country.

Consider Janelle Monáe's visceral "Hell You Talmbout" about police shootings. It's available by streaming, on YouTube and in performance.

"Back in the '60s and '70s, there were only a few widely recognized genres and a limited number of radio stations," Lubet said. "Now you can access all kinds of music without being on broadcast radio."

The rise of the chant

The forms also are changing. Parodies put scathing words to familiar songs. Protest chants are rising, such as Fiona Apple's refrain directed at President Donald Trump at the Women's March on Washington: "We don't want your tiny hands anywhere near our underpants."

Laidlaw wondered if chants are the wave of the future.

"In such a charged political environment, it's tough to be controlled and meaningful," he said. "With a chant, there's no ownership, no barriers to entry. You don't have to sing. You don't even have to be able to read.

"It's inherently populist. You can't have a chant without a bunch of people."

That said, he also pondered the effectiveness of protest songs today.

"These are humbling times to be an artist," he said. "Is it enough to keep doing what we've been doing, or it is time to make the work more pointed? Is it better to spend that time and energy calling representatives and going to protests? Should the art be secondary? That's a hard thing to say, but we have to ask the question."

Listen to a playlist of protest songs below or click here to open it in Spotify.