Two familiar New York voices shared the radio airwaves on Thursday, talking as usual about hip-hop, but up higher on the dial.

Since the ’90s, Angie Martinez and Cipha Sounds were well-known hosts on the influential rap station Hot 97 (WQHT-FM, 97.1). But last year, after two decades, Ms. Martinez decamped for the rival, Power 105.1 (WWPR-FM, 105.1). After a few months of filling her old afternoon slot, Cipha Sounds, too, parted ways with the station, with 17 years on the job.

“Welcome to my new home,” Ms. Martinez said to her former co-worker when he joined her on air. Cipha Sounds said that it “felt a little weird” to be there, but as he eased into his guest D.J. role, he declared, “I’m in the building, ladies and gentlemen!” In recent months, some of Hot 97’s most recognizable names have left the station, while outside voices have come in. As one of the first formatted hip-hop stations in the country, Hot 97 became a distinctly New York institution in the early ’90s, synonymous with the genre’s rise to cultural ubiquity.

But with the loss of so much institutional memory, including D.J.s and hosts who had witnessed the birth of hip-hop, the station risks slipping from its perch as the nation’s premier regional and hard-boiled rap outlet, current and former employees said in interviews. To them, Hot 97 seems to have succumbed to the homogenization of urban radio.