The Dave Grohl produced and directed documentary honoring the late, great Sound City studio continues to move forward with more details, more collaborations, and even a handwritten letter by Dave Grohl explaining why this project is so important to him.

“There used to be a recording studio called Sound City that was in the San Fernando Valley. Nirvana recorded there in 1991. It was this really beautiful dump in the middle of a warehouse district. A lot of great records were made there,” Grohl said. “Fleetwood Mac made records there, Neil Young made records there, Tom Petty, Cheap Trick, Dio, Ratt, Pat Benatar…so I interviewed them to tell the history of the studio, but then I invite them back to record with me, and we make a record.”

Grohl, who has purchased a vintage recording console from the studio, expanded his mission statement for the film by releasing a handwritten note that let it be known this is definitely a passion project.

“In the spring of 1991, I packed all of my belongings into an Army Surplus duffle bag, put my drums in some dusty road cases, rolled up my sleeping bag and jumped into an old, beat-up Ford van headed down to Los Angeles from Seattle,” Grohl wrote. “I was a 22-year-old starving musician without a cent to my name or a place to call home. My destination: Sound City.

“The following three weeks changed my life forever. ‘Sound City’ is a film about America’s greatest unsung recording studio. Deep in California’s sun-burnt San Fernando Valley, tucked away behind train tracks and dilapidated warehouses, it was the birthplace of legend,” he continued. “It was witness to history. It was home to a special few, intent on preserving an ideal. An analog church, a time capsule. The last bastion of a craft defied by technology. It was rock and roll hallowed ground. And it was our best-kept secret. Now I want to tell its story.”

We’re still waiting on a release date for the “Sound City” documentary, which will be distributed by Roswell Films, a division of the label that releases all the Foos Fighters music. Here’s a trailer and video for the movie, a copy of Grohl’s letter, a cassette label that Grohl unveiled at the SXSW Music Festival in Austin, Texas, and a few studio shots with collaborators in the studio.