Etheridge’s voice is, of course, a thing of undeniable and, it often seems, unmatchable power. She’s often been compared to Janis Joplin and not without good reason. I have seen her perform on several occasions and have, each time, been blown away by the sheer strength and broadness of her vocal range. Watching tonight’s show, her voice seems to have acquired yet more gusto and power as she’s aged. Which, frankly, is saying something, given the astonishing vigour and intensity of the instrument she first unleashed on the world almost 25 years ago.

In the space of a single song, Etheridge’s vocals are an ever-evolving musical palette – she runs the gamut from a raucous, gut-wrenching wail of wounded agony to something altogether quieter, more subdued, personally revelatory and profoundly vulnerable. She is every bit as capable of invoking the heartache, anguish, jealousy, unfettered passion and desire that underpin two of her best-known songs, Similar Features and Bring Me Some Water, as she is singing unaccompanied by either her band or her own guitar.

It’s a rare performer than can traverse such intangible and vast emotional terrain with such conviction and resonance, but Etheridge does it with remarkable and impressive ease. Similarly noteworthy is the generosity of spirit with which Etheridge collaborates onstage with her band. Almost every song is an extended riff on the original, delivered in a manner vaguely akin to the way Bob Dylan has long approached live performances: as an opportunity to play with melodies, experiment with instrumentation and have a rollicking good time jamming with the musicians joining you onstage.

“She has always written searing and honest songs about lesbian love and desire.”

Throughout the performance, Etheridge frequently jams with all three of her band members, taking particular joy in riffing off both her guitarist and bassist, though she also often hops up beside her drummer. At one point she even momentarily drums herself, then running back down towards the front of the stage and throwing the drumsticks to the women brandishing the light-up tambourines.

In addition to being a singularly passionate vocalist, Etheridge is also a virtuosic musician. In the studio, she plays both acoustic and electric guitars, as well as banjo, piano, harmonica and mandolin. Tonight she switches between several guitars, acoustic and electric, as well as bringing out the hybrid banjo-guitar, known as a banjitar, on which she composed her latest single, the relatively subdued Falling Up.

As the main set drew to a close with a blistering rendition of Bring Me Some Water, Etheridge exited the stage, her obvious gratitude for the crowd’s whistles and lengthy, thunderous applause evident on her face. She returns moments later to deliver as her encore the song she once described as “one of my best and the one that, when I perform it live, is a transforming song for both the audience and me.”

That song is Like I Do and it remains, all these years later, as vital and immediate as it was when she first recorded and released it. Etheridge plows her way through it, playing the hell out of her guitar and jamming with her band for almost ten solid minutes while still offering up a vocal that is as searing as it is impassioned. Though her time onstage seems to have sped by much too quickly, the crowd leaves sated. We’re all a little enraptured, still spellbound and slightly in awe, I think, of what we’ve just witnessed as we spill out the doors and down the venue’s staircases.

We live in an age of seemingly copious superlatives. So copious, in fact, that I often wonder as I write whether their true meaning is somehow diminished by the sheer frequency with which they’re invoked. Still, make no mistake: Etheridge is a performer par excellence and one thoroughly deserving of every accolade she receives and every superlative linked to her name.

Tonight’s show was many things – affecting, stirring, visceral and unforgettable – but, above all else, it was a rare opportunity to witness a musician at the height of her not inconsiderable musical powers. Passionate, talented and musically intransigent, we can but hope its not another 16 years before Melissa Etheridge graces Australian stages again.

Melissa Etheridge plays two sold-out shows at the Sydney Opera House tonight (Wednesday July 11) and Thursday 12 July. She then plays Canberra’s Royal Theatre on Saturday 14 July (Tickets: Ticketek 132 489 or www.ticketek.com.au), Melbourne’s The Plenary on Sunday 15 July (Tickets: Ticketmaster 136 100 or www.ticketmaster.com.au), Adelaide’s AEC Theatre on Tuesday 17 July (Tickets: Ticketek 132 489 or www.ticketek.com.au) and Perth’s Riverside Theatre on Friday 20 July (Tickets: 132 849 or www.ticketek.com.au)