Working on The New Orleans Beatles Festival has helped organizer Chuck Credo IV understand The Beatles’ music, down to the smallest detail.

“George Harrison loves these little diminished chords,” he said. “If you want to play ‘I’m Happy Just to Dance with You,’ you could say, ’That’s an E, that’s a B’ when it’s really a B-diminished seventh, with his finger kinda not on the fret actually. What we try to do with the festival is try our best to go for broke and figure out what was in these guys’ heads when they were making this music 50 years ago.”

Saturday night’s performance at the House of Blues will mark the 12th year for the festival, which started when members of The Topcats and The Mixed Nuts realized that they knew far more Beatles songs than would fit in their sets, and the demands of the dance floor meant they rarely got to play a song such as “Strawberry Fields Forever.”

The festival started as a chance for them to play those songs, but instead of drawing the 200 people they expected, the show attracted 600.

They knew they were on to something and decided to do it again and expand the songbook. Soon other musicians started approaching them, confessing their love for The Beatles and desire to be a part of the show.

In 2008, the show turned a corner when musicians began to show up at the House of Blues looking to join in. It was also the first year for video, and the band synced its performance of “I Am the Walrus” to the video.

Now, preparing for the show involves a month of weekly practices with a few extra for good measure, and this year Credo and The Topcats will be joined by The Molly Ringwalds, Rockin’ Dopsie Jr., Alex McMurray, Cass Falconer, Robin Barnes, Bill Malchow and Jim Lockwood.

“Tim Shirah from The Yat Pack is going to do a bunch of the early Beatles songs,” Credo said. “This year we’re doing a lot of early Beatles to celebrate that 1964 arrival in America.”

Guitar wizard Jimmy Robinson will perform some of the more psychedelic songs by himself on the acoustic guitar, and the Pocket Aces Brass Band will remake Beatles tunes as brass band songs.

To work up songs for the show, Credo had to dissect the recordings, which gave him an additional appreciation for The Beatles.

For much of their time together, The Beatles only had four tracks to work with in the recording studio. “They recorded three instruments and dumped them on one track, and another three and dumped them on another,” he said. “This is mind-blowing music now, but it was also so innovative. What they did with so little is often overlooked.”

Credo came to The Beatles after hearing his parents play their records, particularly the early albums. When “The Beatles Anthology” was released in 1995, he was in his teens and decided to see what all the fuss was about.

From the start, he was a George Harrison guy, then evolved into a Paul McCartney fan. “John (Lennon) was the last I got into because when he got into his groove is when he got the strangest, The Yoko Ono period.”

In the show, Credo plays Harrison’s parts, and performing them has given him insight into Harrison as a person.

“When you play ‘A Hard Day’s Night’ and “I Saw Her Standing There,’ you can feel the development of George Harrison away from that Chet Atkins, early style of playing, to when he’s at Abbey Road playing ‘Something’ or ‘I Want You (She’s So Heavy),’ and you can feel the influence of Eric Clapton, The Band, and Delaney and Bonnie and all the people he was hanging out with,” Credo says. “You can hear the difference in the way he bends a note.”