<text>  CNNThe 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 TrueFalse fests before its television premiere on May 4th. However, anticipation for the films 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 didnt 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 films companion book, which features a mixture of animation stills, rare photography and other treasures from Kurt Cobains personal archive, no date or further information has been announced regarding the films 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 documentarys score is all unreleased Cobain music. They dont have titles. Before people saw the movie, there were these weird press releases focusing on the unreleased music. And its like: Its a movie. Were not going to stop it and play a song for four minutes, Morgen said. But nobody in Kurts 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. Its a Paul McCartney song. Hows 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 Cobains personal cassettes - Tape 59: Montage of Heck - as a special release on Independent Record Store day, like unannounced, but it didnt happen. See the original story at RollingStone.com. Copyright 2015 Rolling Stone. 