The quiet hum of appreciation that greeted Roberta Flack’s debut album in the summer of 1969 reflected the difficulty experienced by many critics of placing her on the spectrum of black female singers at the turn of the decade. Unlike Aretha Franklin, Gladys Knight or Mavis Staples, there seemed to be no obvious church-raised fire in her delivery. She lacked the raw blues spirit that suffused the voices of Tina Turner or Etta James. And she was certainly not the willing mouthpiece, as Dionne Warwick and Diana Ross had become, of a team of pop svengalis. She was her own woman from the start, and that made her harder to figure out.

As time passed it became clear that there was only one of her near-contemporaries with whom she could plausibly be compared. Like Flack, Nina Simone had studied classical piano and composition before her performances as a nightclub entertainer became the stepping stone to fame. The difference – a big one, rooted in temperament – came in Flack’s ability to accept and enjoy her status in popular music. True enough, after her first British concert at the Hammersmith Odeon in 1972 she told an interviewer – James Johnson of the NME – that “one day I’d like to come back and conduct the London Symphony Orchestra”; she never did, but there were no signs of emulating Simone’s unshakeable bitterness over the career she did not have.

Now reissued in a slightly belated but nonetheless welcome 50th-anniversary deluxe edition, First Take is an opening statement of remarkable vision, authority and maturity. If that is a testament to Flack’s own inherent qualities, perhaps it also has something to do with the fact that she was into her thirties when she recorded it, with years of studying, teaching and performing music behind her. Born in Black Mountain, North Carolina, in 1937, she had been brought up in Washington DC, where she attended Howard University.

Jobs accompanying singers in clubs honed her versatility and led eventually to her own residency at Mr Henry’s, a popular hangout for visiting celebrities. It was Les McCann, a star of the soul-jazz movement, who was so taken with her in 1968 that he taped one of her shows – a tempo-less version of the supper-club standard “All The Way” from that set leads off the second CD in this package – and then, having taken on the role of manager, arranged an audition with Joel Dorn, a bright young A&R man and producer at Atlantic Records.

Dorn, who died in 2007, aged 65, had big ears and a gift for identifying and accentuating the most interesting characteristics of talented artists. After taking Flack into the studio to record the dozen demos that, previously unreleased, complete the second CD, he helped her strip away both the more conventional and the more adventurous elements of her repertoire. Out went the finger-snapping versions of warhorses like “On The Street Where You Live” and “This Could Be The Start Of Something” that others could do at least as well and with greater conviction; also banished was the explicit influence of contemporary jazz evident on “Afro Blue” (a Mongo Santamaria tune that had become a staple of John Coltrane’s live shows) and a recasting of the traditional “Frankie And Johnny” against the modal vamp from Miles Davis’s “All Blues”.

The demos – with Marshall Hawkins on bass and Bernard Sweetney on drums, her regular DC partners – give a pretty good picture of what it would have been like to wander into Mr Henry’s and listen to this unknown singer-pianist leading her trio through a programme of songs seemingly constructed to provide something for everyone. But even casual listeners would have had their ears pinned back by a spine-tingling version of “Ain’t No Mountain High Enough” that seems to prefigure the mood and trajectory of “Tears Dry On Their Own”, the epic of romantic defiance that Amy Winehouse built on the same template.

Dorn would have been particularly attracted to her treatment of a couple of ballads, “It’s Way Past Suppertime” and “The House Song”, which showcase her ability to slow down time almost to a standstill, creating emotional tension through a secure control of sustained vocal tones and a perfect command of silence. It’s hard to imagine the courage it must have taken to develop this approach in the face of the average nightclub audience; eventually, by her own testimony, she could rely on the regular customers to persuade newcomers to show the necessary respect and attentiveness.

No material from these demos was repeated in the running order of First Take, recorded three months later in the same studio, during a mere 10 hours of session time. The album begins with Eugene McDaniels’ confrontational “Compared To What”, first recorded by McCann four years earlier and later becoming famous in his live-at-Montreux version with Eddie Harris. Here, an irresistible riff stated by Ron Carter’s double bass introduces Flack’s measured reading of the angry lyric: “The president, he’s got his war/Folks don’t know just what it’s for/No-one gives us rhyme or reason/Have one doubt, they call it treason.” William Fischer’s arrangement uses half-a-dozen veteran horn players from the Count Basie band to provide soulful punctuations.

Then the album takes a striking and emphatic turn, dropping the tempo way down with “Angelitos Negros” – a setting of a verse by the Venezuelan poet/politician Andrés Eloy Blanco – and “Our Ages Or Our Hearts”, co-written by Donny Hathaway and Robert Ayers, its drama heightened by Fischer’s string chart. Flack takes the traditional gospel song “I Told Jesus” about as far from the Baptist holy-roller model as could be imagined: her subdued, unhurried reading would barely make a candle flicker. As with so much of her music, its power lies in its restraint.

If that is less true of her somewhat placid reading of Leonard Cohen’s “Hey, That’s No Way To Say Goodbye”, it is redoubled for her spellbound version of Ewan MacColl’s “The First Time Ever I Saw Your Face”. This is the song that changed her fortunes when, two years later, it was featured by Clint Eastwood in his film Play Misty for Me, going on to win the 1973 Grammy for record of the year. No longer was she an artist with industry respect but minimal sales.

The tempo lifts to an easy lope for “Tryin’ Times”, written by Donny Hathaway and Leroy Hutson, again riding on Carter’s bass and allowing Flack to give us a hint of her blues chops, before the album concludes with “Ballad Of The Sad Young Men”, a gorgeous saloon song with a melody by Tommy Wolf and a lyric by Fran Landesman. Here she floats Landesman’s rueful, worldly poetry – “Sing a song of sad young men, glasses full of rye/All the news is bad again, kiss your dreams goodbye” – on a cushion of silken strings with all the elegance and attention to the fine detail of timbre and cadence that made her artistry so exceptional. And one thing hasn’t changed in 50 years: the harder you listen to her, the more you’re likely to get in return.