This may sound odd now, but when Donna Summer first hit America's pop music charts in 1975, it was a steamy, scandalous moment.

Her first hit, "Love to Love You Baby," featured Summer making noises of pleasure which sounded seriously sexual, inspiring the BBC to initially refuse to play the record and interviewers to ask what exactly she was doing while tracking the vocals.

But as Summer explains in a clip from HBO's documentary Love to Love You, Donna Summer, the singer was not actually a sultry, sexy seductress.

"It wasn't me, it was something I was playing," she says. "It was a role. Everyone that knew me would call me up and say, 'That's not you, [moaning on the record] is it?' Yeah, it's me."

A secretive artist

Unfortunately, HBO's film struggles to define who Summer actually was, despite knitting together interviews with family members, archival clips and home movie footage — all guided, in part, by her daughter Brooklyn Sudano.

Sudano co-directed the film with Oscar- and Emmy-winning documentarian Roger Ross Williams, searching for meaning in her mother's story. The movie notes even Summer's children sometimes found her tough to know — including one scene in which Sudano's sister, Amanda Ramirez, talks about how secretive their mother could be.

"We were never allowed in her room; the door was always locked," Ramirez says. "We would find out things by reading newspaper articles ... I actually remember the first time that we heard 'Love to Love You.' Didn't even know it existed. Brooklyn came in the room and was like, 'Have I got a song for you to hear!'"

One thing the film does make clear: Summer's towering abilities as a singer, performer and songwriter. It shows how she suggested the title for "Love to Love You"; was inspired by an exhausted restroom attendant to write "She Works Hard for the Money"; and co-wrote the percolating synthesizer riff which powers her 1977 hit "I Feel Love" with disco-producing legend Giorgio Moroder.

Elton John spoke about that song's impact in a clip used by the film: "I remember when 'I Feel Love' came on at Studio 54," he says. "You just stopped in your tracks. What is this? It sounded like no other record."

Summer says they were going for a specific vibe in the studio: "When I went into do it I had the sense that I was floating. And that's what...we wanted to maintain, that floaty kind of — that elation that you feel when you're in love."

Born LaDonna Adrian Gaines and raised in Boston, Summer grew up singing in church. Later, she moved to Germany for a production of the musical Hair and began making records. The film offers lots of performance footage and behind-the-scenes clips, recounting her fights with her record company, abusive lovers and the struggle to be recognized as more than just a disco queen.

But perhaps because Summer held back from her family, the film rarely digs deeply into any aspect of her life before moving on. This is especially noticeable when Sudano asks her uncle Ric Gaines about allegations Summer was molested by a church pastor.

"It became a defining moment in her life," Gaines says. "It's not easy when you don't tell or [don't] have the ability to tell people." But its tough to see exactly how this incident defined her life, or at least why her brother believed it did.

A structure that feeds confusion

The film's structure doesn't help. Subjects speaking about Summer's life are often not shown talking on camera, so it's difficult to know if you're hearing an archival interview or something recorded for the film. And Sudano doesn't reveal much about how she pulled the movie together, making it hard to judge why some elements are used the way they are.

Even Summer's death in 2012 from lung cancer is handled obliquely, with fleeting glimpses of what she went through. Such pivotal moments deserve a bit more detail; without them, the audience remains at a distance.

For those who only know Summer through hits like "She Works Hard for the Money" and "Last Dance," HBO's film offers important context about her talent and lots of great performance footage. But like the artist herself, the film can also be maddeningly enigmatic, just when you want to know more.