(CNN)The HBO documentary "Kurt Cobain: Montage of Heck" is already drawing rave reviews on the film festival circuit, including sold-out showings at both Sundance and the True/False fests before its television premiere on May 4th. However, anticipation for the film's soundtrack is about to hit fever pitch as director Brett Morgen revealed that the accompanying album will feature "a mind-blowing 12-minute acoustic Cobain unheard track," the filmmaker tweeted (via Loudwire). Kurt Cobain documentary set to premiere at Sundance . Morgen didn't share any other details regarding the song other than it will feature on the "Montage of Heck" soundtrack. While an April 7th release date has been scheduled for the film's companion book, which features "a mixture of animation stills, rare photography and other treasures from Kurt Cobain's personal archive," no date or further information has been announced regarding the film's soundtrack. Kurt Cobain doc 'Montage of Heck' adds rarities-filled companion book . Rolling Stone talked to Morgen at the Sundance Film Festival, and the filmmaker revealed that the documentary's score "is all unreleased Cobain music." "They don't have titles. Before people saw the movie, there were these weird press releases focusing on the unreleased music. And it's like: It's a movie. We're not going to stop it and play a song for four minutes," Morgen said. "But nobody in Kurt's life — not his management, wife, bandmates — had ever heard his Beatles thing [a snippet of 'And I Love Her']. I found it on a random tape. It's a Paul [McCartney] song. How's that for shattering the myth?" Sundance 2015: Intimate 'Kurt Cobain: Montage of Heck' doc stuns at premiere . Morgen added that he hoped to put out one of the Cobain's personal cassettes - "Tape 59: Montage of Heck" - as a special release on "Independent Record Store day, like unannounced, but it didn't happen." See the original story at RollingStone.com. Copyright © 2015 Rolling Stone.
The album will feature a 12-minute acoustic Cobain unheard track . The doc is already winning rave reviews . Filmmaker wants to release one of the Cobain's personal cassettes .