Recordings of Michael Jackson's voice on a new album being released this week were far from the finished article and required considerable digital enhancement, according to one of its main producers.

But Teddy Riley, who worked with the King of Pop on several records before his death, believed that "Michael" would go down as a classic, albeit short of the heights of Jackson's heyday in the late 70s and early 80s.

"I had to do more processing to the voice, which is why people were asking about the authenticity of his voice," Riley told Reuters of the first album of new Jackson material since the singer's sudden death 18 months ago.

The project has been mired in controversy since members of Jackson's family were quoted questioning the authenticity of the voice on some tracks and his father's lawyer said the perfectionist would never have wanted the music released.

"We had to do what we had to do to make ... his voice work with the actual music," Riley added in an interview.

"He (Jackson) would never consider it being a final vocal. But because he's not with us he cannot give us new vocals. What we did was utilize the Melodyne (technology) to get him in key.

"With the Melodyne we actually move the stuff up which is the reason why some of the vibrato sounds a little off or processed, over-processed. We truly apologize for that happening, but you are still hearing the true Michael Jackson."

Riley worked on three of the 10 songs on the album -- "Hollywood Tonight," "Monster" and "Breaking News."

The last two were recorded at the New Jersey home of the Cascio family in 2007, along with a third Cascio track "Keep Your Head Up."

It was these recordings that led some to cast doubt over the authenticity of the songs, although Riley, and record label Sony, have been at pains to show they were genuine.

PRICE OF FAME

Riley said much of the negative publicity surrounding the album came from people within Jackson's entourage who did not approve of the project.

"That don't just happen like that, that has to come from somewhere and where it came from was not a great place. It was from a family member, and some family members ... didn't totally get the last say so they kind of hate the project.

"So there you have it, a chain reaction, a domino effect that makes the credibility of Michael go down," he said.

"I am here to protect that, because I know it's him, I know it's great material, I know that it needs to be out, I know that the legacy needs to continue because he's such a great person, and there's more to come."

"Michael" is the first album of new Jackson material since "Invincible" in 2001, and the first in a reported $250 million deal between Sony and the executors of Jackson's estate to release 10 albums through 2017.

Author J. Randy Taraborrelli, who wrote a 1991 best-selling biography of Jackson, said on Monday that Jackson's estate had another 60 songs but did not plan on releasing all of them

"They've got 60 incomplete songs but they've only got about 20 left with vocals that they feel, that the estate feels, are worthwhile," Taraborrelli said in a U.S. interview on the CBS TV network's "The Early Show".

"They're not releasing everything. They're releasing the things that they believe Michael would want released, and that's about 17 to 20 more songs," Taraborrelli said.

Asked if he would agree to produce future posthumous Jackson material, Riley replied:

"If it was my decision, yes, I would be involved in anything that Michael was involved with. If they will have me I will definitely be a part of it. I'm here, I came out here to be a servant to my friend."

Among the topics Jackson tackles on the new album is people's thirst for fame and the high price of becoming a star.

In "Hollywood Tonight" he describes the real-life experiences of an unnamed friend who heads to Los Angeles aged 15 to make it in the movies, and in "Monster" he sings about the paparazzi.

"The Monsters are the ones who, when you're up they come to get you and they beat you down and when they get you down they go to the next artist," Riley said of "Monster."

"That's their job, to hit you while you're up and step on you while you're down, and that's what he always said."

Reviews of "Michael," which hits British stores on Monday and U.S. stores on Tuesday, have been generally positive.