Garbage trucks rumbled past a street corner café on Second Avenue one recent morning as Diamanda Galás sipped her espresso. She was dressed like a crow, in black from head to toe, and enthusiastically began a conversation that ranged from her affection for Spanish horror films to the time, in the early 1970s, when she decked the critic Stanley Crouch in the midst of an argument about the blues.

“I smacked him right across the face and made his mouth bleed,” the singer, never one to avoid life’s visceral moments, said.

Ms. Galás isn’t the first performer to take a swing at a critic, but her fighting spirit is definitive. Ever since her 1981 debut album “Wild Women With Steak Knives,” the San Diego native has been a defiant force, applying her three-and-a-half-octave range to everything from American folk ballads to the famed Greek composer Iannis Xenakis, transforming much of the material into something that can be at once terrifying in its intensity and spellbinding in its vision. “Beauty will be convulsive or not at all,” André Breton wrote. Listening to Ms. Galás, you can understand what he meant. She sings with a power that is shattering and sublime.

She is also unpredictable. For a series of concerts that begin tonight at the Highline Ballroom, Ms. Galás intends to survey several different traditions. She’s devoted two evenings to romantic standards, French ballads, and the “homicidal love songs” from her pending November release “Guilty, Guilty, Guilty” (Mute), which features surprises such as O.V. Wright’s classic R&B weeper “Eight Men and Four Women.” A third concert will be built around the Amanedhes, improvisatory cries of sorrow that reflect on the singer’s Greek heritage, as well as rembetika songs, the “hashish music” of Greek and Armenian outlaws exiled from Turkey.

The programs are a hint not to trust appearances, even those as dramatic as Ms. Galás’s, who has been favorably compared to “a lizard queen” and “a demon going to war.” She doesn’t seem to mind the labels, even when they are inaccurate or sloppy. But it does make for confusion

“When you’re considered the kind of freak that I’m considered to be — lesbian, dyke, goth, screamer — and then I sing Jacques Brel, some people are like, ‘What is that?’ or, Juliette Gréco, ‘What is that?'”

Appropriately, the 51-year-old singer is as aware of her audience as it is of her.

“What are they going to make of Ralph Stanley?” she asked, alluding to a new recording of the bluegrass legend’s conversation with the Reaper, “O Death,” which found new popularity on the soundtrack of the Coen Brothers’ 2000 comedy, “O Brother, Where Art Thou?” “Especially my version! I don’t want to do Ralph Stanley the way Ralph Stanley does Ralph Stanley, because we don’t need that. If you’re going to do it in a respectful way, who needs that? If anything can be learned from Ornette [Coleman], it would be that. He was playing the blues, and people would say to him, ‘It’s obvious you never heard of John Lee Hooker the way you play the blues.’ He would look at them like they were an idiot.”

Ms. Galás, who began singing professionally at 13 with her jazz pianist father and made her performing debut in 1979 at France’s Festival d’Avignon, really loves this topic.

“I worship the singers who sang it straight,” she said. “They actually knew the melody. They knew the changes. They could sing over the changes. They weren’t just going up there and doing their thing over the top of it. That’s disgusting. That’s what you hear on ‘American Idol.’ I can play it as straight as Doris Day. Love her. Best legato in the business. And from there you can take the song to another place.”

That’s an ideal way to describe what happens in “O Death.” Ms. Galás accompanies herself on piano, playing gutsy, rippling notes that hang in the air like a deftly poised dagger in a New Orleans bawdy house. She introduces the lyrics as if her lungs were a dark, forgotten cave, the words sepulchral, final. Before too long, she launches into a succession of improvisations — dizzying variations in pitch, piercing wordless leaps up the scale, ecstatic, explosive, an extreme aria that loops stratospherically and plunges back into bluesy vigor.

“I was reading a forensic book about a good ol’ boy in Louisiana who has a body farm,” Ms. Galás said, offering a roundabout perspective on her creative choices. “He was a forensic pathologist who had seen so many horrific murders of women and children. So he has a body farm where he lays the dead bodies out in different climactic situations, where he could determine how long it takes for the body to rot to the bone. I was reading that and working on ‘O Death.’ I was in Hollywood with this drag queen buddy of mine, and he was reading the book out loud in his Bermuda slacks. He has a coffin laid out in his living room, with all these death things, a whole New Orleans-Kentucky funereal decor.”

When the singer returned to the studio, she came up on the line “flesh and worms will have your soul.” “And there it was,” she continued. “There’s this section where I go into what some people call vocal multiphonics. I’m pitching it, that came out of nowhere. But it was based upon that reading somehow. You know, when you’re singing multiphonics on a scale, you’re using the resonance cavities in your body to make three or four notes at once. When you start talking about resonance cavities, then you’re back to that forensics guy. The music is on a scale, which is like walking along a path, the inescapable path that death is leading you on.”

She paused for a moment and considered the analysis, then offered a disclaimer. It’s not as if she plotted all this in advance.

“I can’t think like that,” she said. “But basically it’s as if you’re singing and suddenly you get hit upside the head by something.”

Just ask Stanley Crouch.

Ms. Galás will perform tonight, August 12, and August 19 at the Highline Ballroom (431 W. 16th St., between Ninth and Tenth avenues, 212-414-5994).