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The story behind the famous ‘dun-dun’ sound on ‘Law & Order’

These are composer Mike Post's stories.

You don't even have to be looking at the screen to know an episode of the "Law & Order" franchise has just started or transitioned to a new scene.

All you have to do is hear the iconic sound: dun-dun.

As a reboot of the original "Law & Order" gets set to premiere Thursday on NBC, the famous sound effect created by composer Mike Post will once again be a crucial part of the show.

Post said in an interview with the Television Academy Foundation that it all began when show creator Dick Wolf called him to come up with some music after Wolf had a script for the pilot of the original "Law & Order" back in the late 1980s.

Wolf had previously been a writer on "Hill Street Blues," a hit 1980s cop drama on NBC whose famous theme song was also written by Post.

Post watched the pilot for "Law & Order" and really liked it, so he wrote the show's theme song, which has become another beloved piece of music for "L&O" fans over the years.

Once the show was picked up by NBC ahead of its premiere in 1990, Wolf called Post with another request.

"He called me after and he said, ‘Hey look, you know those cards (on the show)? I said, 'Yeah, the location and the time stamp?' He said, 'I need a sound for it.' I said, 'Talk to sound effects.'"

Law & Order: Special Victims Unit
It wouldn't be an episode of "Law & Order: SVU" without the iconic "dun-dun" sound. Chris Haston / NBC

Wolf pleaded with Post to create the sound himself.

"He laughed and said, 'Can’t you come up with something? Please, come up with something that’s really distinctive,'" Post said. "He said, 'You watch, it’ll end up being important.' I went, ‘You’re crazy, you don’t know what you’re talking about.’"

Post told "The Law & Order: SVU" podcast in 2020 that he sampled the sound of a jail door slamming shut as well as the sound of a man hitting an anvil with a hammer and some different drum noises his team came up with in the studio.

He thought it needed more "heft to it," so he incorporated a sound he found of 100 men stomping on a wood floor in Japan.

Not only is the sound iconic to "L&O" fans, it's music to the ears of Post's bank account. He has a different name for it than "dun-dun."

"It’s not a sound effect, it’s a piece of music that actually gets a royalty," he told the Television Academy Foundation. "I call it the 'ching-ching' because I’m making money off of it."

Post has since done different versions of his famous compositions for the show's multiple spinoffs, most recently "Law & Order: Organized Crime" starring Christopher Meloni, which premiered last year.

His creations have become part of the sonic landscape of television for decades, as the original "Law & Order" ran from 1990-2010 and is now being revived with a cast that includes stars Sam Waterston and Anthony Anderson. Meanwhile, "Law & Order: SVU" is the longest-running prime-time U.S. live-action series in TV history in its 23rd season.

"Every time Dick comes up with another show, he calls me and says, 'OK, it’s time for another variation,'" Post said.

Post has created a pair of legendary TV theme songs for "Hill Street Blues" and "Law & Order," but he may end up remembered most for the "dun-dun" he tried to brush off to the sound effects department.

"After maybe a year or two or three, Dick sends me a note one day that says, 'Now, smart guy, what do you think of this? On your headstone, you’re going to be known for two notes that aren’t even notes,'" Post told "The Law & Order: SVU" podcast. "Everything you’ve written that’s pretty good, and you’re going to be known for the one thing you didn’t even want to do."