Los Angeles, California (CNN) -- Songs that didn't make the cut on Michael Jackson albums while he was alive and some forgotten recordings left behind on computer hard drives will be on an album released this fall, sources familiar with the project say.
Jackie Jackson, one of the singer's older brothers, has been working in a studio to help prepare the album, which will include 10 previously unheard songs, according to Jackson estate spokesman Jim Bates.
Jackson's estate and Sony Music announced in March that his next album of unreleased music will go on sale in November.
Music producer Rodney Jerkins, who co-produced Jackson's 2001 album "Invincible," has been working with Sony to put together the new album, a source familiar with the project said. The source asked not to be identified because he was not authorized by the record label to disclose details.
John McClain, one of the two men named in Jackson's will to be executors of his estate, is also working on the album with Jackie Jackson, Bates said. McClain owns a recording studio in Hollywood.
Jackson was known to rent out Los Angeles recording studios for weeks at a time for creative sessions, sometimes alone and sometimes with other well-known artists.
A producer told CNN that he was surprised to find a large cache of forgotten Michael Jackson music files stored on a hard drive at a Hollywood studio in the months after Jackson's June 25, 2009, death.
When he turned the recording device on to start a session, he heard Jackson singing "Hot Fun in the Summertime." The 1969 hit by Sly & the Family Stone is part of an extensive music catalogue that Jackson bought.
The producer said he made a backup copy of the 40 gigabytes of Jackson music and turned it over to one of the Jackson estate administrators. He asked not to be identified because of the sensitivity of the matter.
Another computer hard drive with music was found in Jackson's rented mansion in the days after his death, Bates said. A Jackson family member later handed the hard drive over to the estate administrators, he said.
It was not clear if any of that music will be included in the upcoming project, but Sony's Columbia Records has a contract with Jackson's estate for 10 albums of unreleased material over the next seven years.