At 77, Ms. Baez certainly doesn’t carry herself as if she has any intention of slowing down. On a recent afternoon, she interrupted a walk around her backyard to unlock her chicken coop and chase a dozen birds through the dirt. After rounding them back up, she was delighted to find a handful of new eggs, which she carefully carried up to her kitchen. In the house, the furniture was well worn, but the rooms felt spare and airy, perhaps because she’s “decluttering” using the Marie Kondo method and is proudly down to three shirts in her closet.

The crystalline purity of Ms. Baez’s soprano rang out from the 1963 March on Washington to Woodstock six years later, from Live Aid in 1985 to the protests at the Dakota Access Pipeline less than two years ago. But it was changes in her vocal range that mostly led to her decision to retire.

“I asked my vocal coach many years ago when it would be time to stop,” she said, “and he said, ‘Your voice will tell you.’ And it has — it’s a muscle, and you have to work harder and harder to make it work.”

She started seeing a vocal therapist six years ago, which led to “an easing up, and finding more pleasure in the singing.” But it also meant coming to terms with a different sound. “I’ve gotten to like where I am — partly,” she said. “This is what I got, I don’t have any more than this, so what am I going to do with it? And that was a big step. It quit all the nostalgic [expletive] about what I wanted to sound like, and I was willing to give up the high notes because they weren’t working anyway.”