When Barker left the VCA, she remained a student of her renowned elder, who, she discovered, “let her guard down in private and you got to know the real Joan Hammond. In a class situation she was very much the Diva, but in a one-to-one lesson she had a wicked sense of humour and you could have a laugh with her”.

There were other benefits, too: “To know she had faith in me as a performer and to have her put so much time and effort into my voice gave me great confidence and helped me develop by leaps and bounds”. With her mentor’s voice “still very intact and fresh, sounding like it did on her recordings”, Barker learned the importance of interpretation of text as well as of music.

“She was adamant that the whole point of singing was storytelling, and to do that you needed to live the moment in the music. Sometimes she would demonstrate, and to hear the power and the sound of her voice in the flesh, just made sense of everything!”

Half a lifetime later, and with an international career to match that of her mentor, Barker travelled to Brisbane earlier this year to record her tribute to Hammond – with  Guillaume Tourniaire conducting the Queensland Symphony Orchestra – all too aware of the parallels between their careers.

“A lot of my repertoire, surprisingly, was her repertoire, even though our voices are completely different. She had a much bigger, stronger, very unique sound; more a lyric-dramatic soprano, a spinto type, whereas I’m more lyric. Some of the big Verdi pieces she sang I would avoid, but certainly things like Butterfly, Traviata and Rusalka I also do.”

Hammond’s imprint and influence on Barker has made itself felt in other ways, too. “I often wonder if she’s had a guiding hand in inspiring people to offer me particular roles that were in her repertoire. It’s strange, but it would be nice to think so.”

Barker’s tribute begins with a composer that some might be surprised to find was in Hammond’s repertoire at all: Jacques Offenbach. No less surprising, perhaps, is the aria in question: ‘Elle a fui, la tourterelle’ from the composer’s only fully operatic score, Les contes d’Hoffmann. There is probably little else that he wrote that is so concentrated or intense.

“It’s a simple sounding aria and the sort of piece you would never have imagined Joan Hammond singing,” says Barker. “It’s got a passage with very high, demanding tessitura, but for any singer who deals with a lot of repertoire where you really have to drive the voice, it’s really good for your technique to come back and sing something as simple as ‘Elle a fui’. She clearly understood that it was important to keep your voice oiled in all sorts of facets rather than just one.”

Two of the most deceptively simple (and ravishing) arias on the disc – ‘When I am laid in earth’ from Purcell’s Dido and Aeneas and ‘Glück das mir verblieb’ (better known as ‘Marietta’s Lied’) from Korngold’s Die tote Stadt – proved to be the most challenging for Barker.

“The Purcell might sound as simple as anything, but it’s an incredible, very exposed aria. There’s nothing underneath, no cushion from orchestration.”

And the Korngold, a duet in the opera and sung here, as is the custom for solo performances, with the soprano taking some of the tenor’s lines, is “just so beautiful; a lovely, lovely, gorgeous aria”, Barker cautions that “both with it and the Purcell, you have to really keep in control of yourself. It’s one of the biggest challenges of singing in opera: keeping a hold on your own emotions in performance.”

Control is a hard-earned skill for any singer, and something that Barker says she learned from Hammond: “She had incredible discipline in every part of her life, on stage especially”.

But Hammond also had a keen sense of taste, timing and theatre as well, her Tatyana’s Letter Scene from Tchaikovsky’s Yevgeny Onegin an indelible high-water mark in her career. And her recording of ‘O Silver Moon’ from Rusalka encouraged Sadler’s Wells to stage Dvořák’s then neglected opera in London in 1959, effectively re-introducing it to audiences around the world. On Barker’s disc, it seems to function like the last track on Side ‘A’ of an LP – a gentle, bewitching standing still of time before the turbulence and high drama that is to follow on Side ‘B’.

Given that Hammond was an especially noted singer of Verdi’s heavier roles, it comes as no surprise to find the composer featured three times on Barker’s tribute disc. It was a daunting prospect, Elisabetta’s ‘Tu, che le vanità’ from Don Carlos completely new to her.

“In fact, nearly all of it was new to me. There was a lot of learning! I had done Tatyana before but not for a few years. Don Carlos and the Korngold were completely new. Other things I had done before, but a long time ago, which meant more or less re-learning them. It was tough recording them in four days because they are so contrasting, and long and arduous. I was pretty exhausted by the end.”

A soothing encore (one that also serves to offer no less eloquent evidence of the breadth of Hammond’s repertoire) comes in the shape of four songs, accompanied by piano, more familiar to the salon and the drawing room than to opera houses and concert platforms.

Three signature songs summon up a different, less Olympian image of Hammond: Home, Sweet Home, The Last Rose of Summer and The Green Hills of Somerset, a song with which Barker has her own particular relationship: “I used to do callisthenics to it as a child, over and over, again and again – and I absolutely hated it. And even now, whenever I hear it, I immediately want to touch my toes!”

There’s a novelty item, too, one that has an especially direct link between Hammond and Barker – Shadows, a song written for Hammond by the Australian composer Ronald Settle.

“And I’ve got her copy of the score!” reveals Barker. “I found the music in my music, so at some point she must have given it to me to learn. I don’t know if she ever sang it, but it’s a fantastic, very dramatic song, with wonderful words that sum up her own life as a singer – ‘You won’t be forgotten while I remember you’ is the final line of the song.”

Barker says she “counts myself lucky that I knew Joan Hammond because she was an extraordinary person. She sang every thing with her full voice, she was never precious. That was what was so astonishing when you listened to her.”