“My parents were upset and tried to talk me out of it,” she writes in the book, published Sept. 17. “When it became apparent that they couldn’t change my mind, my father went into the other room and returned with the Martin acoustic guitar that his father had bought in 1898.

“When my father began singing as a young man, my grandfather had given him the instrument and said, ‘Ahora que tienes guitarra, nunca tendrás hambre.’ (‘Now that you own a guitar, you will never be hungry.’) My father handed me the guitar with the same words. Then he took out his wallet and handed me thirty dollars. I made it last a month.”

Her grandfather’s words were prophetic, setting the stage for a career that’s stretched across five decades and more than 30 albums. Thanks to her unparalleled voice, Ronstadt became one of the most successful and emotive rock and pop singers of the 1970s, not to mention the only artist ever who’s earned Grammy Awards in country, pop, Mexican American and Tropical Latin categories.

But in August, Ronstadt, 67, revealed that she wouldn’t be singing anymore because of the effects of Parkinson’s disease.

“It happened gradually,” she said in an interview recently with an almost matter-of-fact tone about losing her ability to sing. “I was struggling for so long, at some point it was a relief [to get the diagnosis and] not to have to struggle anymore. What happens with Parkinson’s is that in the brain there’s faulty wiring, like the communication cables are broken. My vocal cords weren’t getting the message.

“Singing is extremely difficult. There are a huge number of little vibrations that have to be coordinated in an exclusive way to produce a sound, to color, to shape, to make an emotion, and you don’t do it on a conscious level. The muscles have to respond to infinitesimally subtle thoughts, whims and energy. Now I have a hard time calling my cat,” she said with a laugh.

Yet in person Ronstadt navigates the twists and turns of an open-ended conversation like an Olympic slalom champion, deftly swooshing from one subject to the next with informed and passionate positions, whether it’s her belief in the importance of exposing children to music early to immigration policy, the dangers of media ownership being concentrated in fewer and fewer hands or what she sees as the rapid deterioration of the nation’s cultural well-being.

Parkinson’s is making it a chore for her to walk from her Beverly Hills hotel room to the downstairs restaurant for a bite (she routinely carries a pair of ski poles with her to get around). She was in Los Angeles from her Bay Area home on a three-week, eight-city book tour in support of “Simple Dreams” (Simon & Schuster, $26), which carries the subtitle “A Musical Memoir.”

“I’ve been spending some time with David Hidalgo,” she said, referencing the singer, guitarist and songwriter of L.A.’s venerated rock band Los Lobos. “I’d always wanted to sing with him, and I finally did,” she said shortly after easing herself into one of the restaurant’s booths. She leaned against a large pillow to help ease her back pain. “We talked about doing a duet album, but my voice had already started to go. I couldn’t do it, and that makes me furious.”

There’s little bitterness, however, evident in her amenable demeanor. She smiles easily and laughs frequently, yet her longtime friend, producer and manager, John Boylan, says the book tour “is harder than any rock tour I’ve done over the last 40 years. It’s very hard on her.”

But when addressing the effects of Parkinson’s (which she’s convinced she’s been struggling with for years even though she got a confirmed diagnosis only a few months ago), Ronstadt does so dispassionately and with humor. It’s as if she’s channeling what she witnessed as a child when her mother’s back was broken in a car accident. Ronstadt recalls in her book that it wasn’t until the following morning, when her mother collapsed in their kitchen, that the family realized she’d been terribly injured.

“She stayed calm, so I wasn’t aware that anything was particularly wrong,” writes Ronstadt, who has two grown children of her own. “My father was helping her, and he was pretty calm, too.”

She displayed the same sense of calm last week during a public question-and-answer session and book signing in Santa Monica. Ronstadt couldn’t immediately conjure the name of someone she was telling a story about, quickly dismissing it with a laugh as “Another Parkinson’s moment!”

“Simple Dreams” recounts a career propelled by more than Ronstadt’s voice. It takes readers on an engaging journey from her beginnings as part of a large, extended Mexican American family in Tucson through the Los Angeles music scene of the 1960s to the heights of her music stardom in the ’70s and ’80s.