Polachek, a 37-year-old singer-songwriter-producer who emerged as part of synth-pop act Chairlift before striking out on her own, is touring in support of her excellent new album “Desire, I Want to Turn Into You.” That title served as the chorus of her opening number, “Welcome to My Island,” which set the tone for the night: a whistle register that can cut through the most crystalline synthesizers, hey-hey-hey fist pumps and a sensual approach to romantic devotion. “Hope you like me,” she sang, “You ain’t leavin’.”

Not that anyone in the sold-out crowd wanted to depart the island Polachek and Co. created. In front of stage design dominated by volcanic shapes and rooted in an expression of the classical elements, the singer stalked like a gazelle, her waiflike figure all body rolls and half-time vogue hands.

As the background projections changed, so did the songwriting touchstones, with Polachek and her three-piece band guiding a trip to “Tom’s Diner” and walking through a Savage Garden, with the breakbeats and scintillating arpeggios of warehouse raves, her voice more automatic than Auto-Tuned. At one point, she performed “Crude Drawing of an Angel,” a smoldering song about intimacy and her contribution to a genre she said she didn’t create but did name, a combination of scary and horny that she jokingly called “scorny.”

But it’s her opera-trained voice that kept the audience enthralled and enamored. Whether twittering like birdsong, riding roller coaster vowels, swelling like a yawn or ringing out like tubular bells, Polachek’s instrument is the human complement to synthetic songs that bridge pop music’s halcyon past and optimistic future.

Accompanying Polachek into the unknown was her sonic and aesthetic opposite, but equally talented singer-songwriter, in featured guest Ethel Cain. Instead of earthen geometry, Cain performed in front of a grainy loop that felt like B-roll from “True Detective” or “The Texas Chainsaw Massacre,” matching the Southern gothic vibes of her music.

Whether breathy or weighty, Cain’s voice is a melancholic salve amid blown-out songs that give her lyrics space to wander. Despite performing little more than a handful of dirges and ballads about Friday night football, Southern Baptist churches and sleazy dead-end strip clubs, Cain elicited a similarly rapturous reaction that would eventually greet Polachek.

“God loves you, but not enough to save you,” Cain sang with arms wide open, “So, baby girl, good luck taking care of yourself.” But who needs luck when she and Polachek are proving that post-monoculture pop stardom is whatever you want it to be?