When Dave Grohl and the Foo Fighters record an album, they do it their way.  The last time around, Grohl bought the vintage board from the legendary Sound Studio in L.A., installed it in his basement studio, and recorded to analog tape - something virtually unheard of in our digital world.

We heard several months ago  that the Foo Fighters were writing and demoing material for their eighth album, but we had no idea exactly what the process would be this time around.  Now we know.

The Foo Fighters are apparently visiting cities with rich musical traditions - Chicago, Nashville, Austin, Los Angeles and now New Orleans.  And from all indications, Grohl's interest in the documentary world (Sound City) has led him to document the recording process for an upcoming HBO series.

For their New Orleans headquarters, the Foo chose the historic Preservation Hall, a venue known more for the Jazz echoing through it's hallowed halls than the Foo Fighter's pop-rock stylings. A temporary studio – with analog, rather than digital, recorders – was installed in an office behind the Hall's courtyard.  Grohl wrote lyrics for the designated New Orleans song after immersing himself in the city – and interviewing various musicians — for days.  To produce the track, Butch Vig - the man behind Nirvana's "Nevermind" - was brought in.  The venue was closed to the public, with a sign reading "Closed this week for a Private Event."   And the band rehearsed.  And recorded.  And then it was done.

With the song complete, and the band's time in NOLA coming to end, Grohl and Company pulled the ultimate surprise.

On Saturday, the band tweeted a picture of Grohl with the Preservation Hall Jazz Band's Charlie Gabriel and Freddie Lonzo, along with the teaser, "So...NOLA, what're you guys up to tonight?"

Word traveled by tweet, Facebook, and word of mouth throughout the city, and by late afternoon, St. Peters Street - in front of Preservation Hall - was closed due to the sheer number of people crowded in front, hoping to get a glimpse of what was happening inside.

What happened inside was a 90-minute Foo Fighters set for VIPS and invited guests, who watched through two doorways leading into the music area of the hall.  In true Dave Grohl fashion, at a point in the show's hit-after-hit-after-hit extravaganza, the leader of the Foo Fighters moved aside a barricade in front of one of the doors, so that the crowd outside could get involved in the melee.

According to nola.com, before kicking into the final Foo Fighters song of the night ("This is the Call"), Grohl announced to the crowd,

"we've been to a lot of great places, we've jammed with a lot of great people, but this week in this city has changed our band forever."

Maybe a zydeco album is in their future?  Nah...couldn't happen.  But it did, you know Dave and the Foo Fighters could pull it off.

Check out some fan filmed video of the super-secret-surprise show below: