In a doctor’s waiting room in Lafayette, La., Emma Benoit was puzzled: A bespectacled academic was there with a hulking machine that looked like a wooden closet. He wanted her to speak into it.

The man was Lorenzo Dow Turner, a pioneering Black scholar of linguistics. He was crisscrossing southern Louisiana in the summer of 1935 with an enormous recording device that weighed 100 pounds and required at least two people to carry.

Ms. Benoit leaned toward the machine and began outlining the “passing of my life.” A 69-year-old widow, she was born in the ashes of the Civil War to a formerly enslaved mother and a white father. She spoke in Louisiana Creole, a language that only a few thousand people now use but was once the predominant one in parts of the state.

Nearly a century later, the machine’s aluminum disc recordings were analyzed and shared publicly on Friday for the first time. Oliver Mayeux, the Cambridge University linguist who found Ms. Benoit’s interview alongside 12 others from Dr. Turner’s trip, said they were the oldest known examples of someone speaking Louisiana Creole, also known as Kouri-Vini. (Older recordings exist, from 1934, but the language is sung rather than spoken.) The rediscovered clips were housed at the Archives of Traditional Music at Indiana University Bloomington.

“The moment I heard these recordings, I knew that they would drastically change our understanding of this language,” Dr. Mayeux said. His research findings were published in the journal “Language Documentation and Description.”

For linguists, the discovery sheds light on how Louisiana Creole emerged from its roots in chattel slavery, blending French, West African and Native American languages. The clips offer historians an unusually direct glimpse into the lives of the language’s long dead speakers, who have remained largely sidelined from the historical record. To the direct descendants of Ms. Benoit, they are a trove of family history.