Mix one part Jay-Z with two parts Linkin Park

You flip the radio dial and hear a blurry wash of rock guitars. Ah, it’s one of the season’s signature rock songs, “Boulevard of Broken Dreams” by Green Day. No, wait -- isn’t that Liam Gallagher’s wavering, nasal voice? The song must be the Brit-pop classic “Wonderwall” by Oasis. Hold on -- now it sounds like Travis and, uh, can that really be Aerosmith?

Don’t adjust your radio or bother trying to sing along. You’re caught in a mash-up. We live in a culture of reruns, recycling and “re-imaginings” and the example of the moment is the song described above, one of several “mash-ups” that are being played on radio stations such as rock giant KROQ-FM (106.7) and, even more often, on its upstart challenger, Indie 103.1.

Crafted with the help of the latest music software, mash-ups might be considered an application of Reese’s theory of synergistic yield: two great tastes that taste great together. “They are ear-catching,” said Indie’s program director, Michael Steele. “They can be amazing.”

They are also catching the attention of MTV (in a big way, with a key series devoted to mash-ups) and the world’s largest record company, Universal Music Group (in a small way, with the first commercially released single of a mash-up song).

The mash-up in some form or another has been around for a decade, but the scene crystallized for outsiders last year when Danger Mouse, a record producer, completed his aptly named “The Grey Album” -- a mashing of the Beatles’ so-called “White Album” and Jay-Z’s “Black Album.” It was an underground sensation and a legal sore spot -- the custodians of Beatles music quashed its widespread release as a CD, a very public reminder to mashers that although their hobby isn’t illegal, attempting to profit from others’ music without permission will put lawyers into billable-hours mode.

So “Grey” never made it to stores, but it percolated far enough into the mainstream that Entertainment Weekly named it the best album of 2004.

The term “mash-up” first caught on in England and it no longer seems to strictly refer to a track made from vocals from one song put over the instrumentation from another. Now mash-ups can be handful of songs and voices and music getting all, well, mashed up.

The blending, blurring, banging or stitching together of two or more songs has been a core move for hip-hop and electronic dance DJs since they first put together two turntables and a microphone. What’s changed is that now the urge to merge is catching on in a big way in the rock scene.

“If we put it on and it’s a special one, boom, just like that it can be No. 1 with phone requests,” said Matt Smith, music director of KROQ-FM (106.7). Smith first noticed the mash-up potential last year when the station experimented with a cocktail of “In Da Club” and “Closer,” tracks by 50 Cent and Nine Inch Nails, artists who have numeric nicknames and little else in common.

Smith said there are a barrage of mash-ups now for reasons of both technology (“It keeps getting easier with the software,” Smith said) and widening exposure. But, Smith said, as a steady serving, he thinks the songs are more cotton candy than bread-and-butter.

There are bazaars of mash-ups on the Internet, where file sharing gives a wealth of source material and the blog culture dovetails with the mash-up tenets of digesting, personalizing and posting that source material.

There’s plenty of intrigue too in browsing the vast folk library that has sprung up. Who wouldn’t want to check out John Lennon wailing with the White Stripes, Beyonce’s “Crazy in Love” trading time with Led Zeppelin’s “Moby Dick,” or the morals-code meltdown suggested by the partnering of Madonna and the Sex Pistols?

Tom Calderone, executive vice president of MTV’s music and talent programming, said the allure is why MTV banked on mash-up magic last year with “Collision Course,” which left the mashing not to a DJ but to the artists. The music station brought New York rap sultan Jay-Z to L.A. to meld his hits with the wail of Linkin Park.

There is no debating the commercial appeal; the resulting live CD debuted at No. 1 on the U.S. pop charts and MTV is now in discussions to follow up with shows this year that include proposals that would pair Green Day and Ludacris, Missy Elliott and Maroon 5, and Coldplay and Justin Timberlake. The station is also in talks with 50 Cent to see which artist he might see as a meld candidate.

Unlike tapping two stars for a duet, the unique challenge of the MTV-defined mash-up is getting artists who can sonically fit their songs into the same space, thematically and musically. “It’s easy to do a duet.... To do this you have to really be a musician and you have to really be an artist just to figure out how you are going to do it.”

The appetite for DJ-crafted mash-ups is deep enough that every Friday night on rock powerhouse KROQ-FM in New York (it has the same name as the L.A. station, but an unrelated business entity) fans tune in to hear DJ Muggs of the L.A. hip-hop crew Cypress Hill play the latest mashed submissions sent in from pros and amateurs alike.

Here, Indie 103 is the most vigorous player of mash-ups, but it’s not the most surprising. That title goes to oldies flagship KRTH-FM (101.1), which recently has been playing a mash-up of the Beatles’ 1969 hit “Get Back” with the fiery 1971 reworking of the song by Ike and Tina Turner.

Program director Jay Coffey said the move was directly inspired by the mash-ups he heard on KROQ and that there will be more coming.

“You’re constantly looking to do something new when you’re an oldies station even if it’s smoke and mirrors because, with oldies, it’s not like there’s new ones coming out,” Coffey said. “We’re working on more now and the listener response has been great.”

Coffey, a veteran of nearly three decades on the L.A. dial, also reminded today’s mashers not to presume that their new technology means they are pioneering a new idea.

“The first mash-up might have been ‘You Don’t Bring Me Flowers,’ ” he said of the melancholy 1970s hit. “A DJ took the version by Neil Diamond and put it together with the Barbra Streisand version and it took off. It’s a lot easier to do now, but that was really big. It was a platinum hit. What’s going on now is just taking an old idea and putting it together in a new way.”

Radio is happy with the mash-ups whether they are novelty or fertile new ground. But what about record companies? It’s been a mixed bag, which is fairly apt for a DJ creation. This month, officials at Universal’s Interscope Records proudly noted that their distribution of “Frontin’ on Debra” marks the first time a major label has commercially released a single that is a DJ-crafted mash-up. The single integrates the quirky 1999 Beck mash-note of a song called “Debra” and the bouncier “Frontin’,” the 2003 track from Pharrell Williams with Jay-Z.

That type of release seemed very unlikely last year when EMI Music, the Beatles’ publisher, fired off a cease-and-desist letter to the interested parties looking to release a CD of Danger Mouse’s “The Grey Album.” The Mouse himself, who is a record producer named Brian Burton, has been hailed for the ingenuity of “Grey” and defended his genre by noting that he and others in the experimental field do not seek profit or intend trademark harm.

Why all the “Grey” work then?

“It sounds cheesy, but it’s for the love,” he told The Times. “That’s why I did it. It was so gratifying. When I was finished, it was the biggest sense of accomplishment I’ve had over anything.”