3. The simple answer is that singing prevents vocalists from stressing syllables, according to Josef Fioretta, a linguistics professor at Hofstra University.
“What gets lost in singing are the suprasegmentals,” a linguistic term used to indicate qualities like stress, tone, and syllabification, Fioretta said. In other words, a song’s rhythm can limit a singer’s ability to pronounce words, and especially vowels, in his or her usual cadence: “The tone, the intonation, the rhythm of a language; these all get lost in singing,” he says.
4. When syllables aren’t emphasized like they are in a normal speaking pattern, they become neutralized, Fioretta explained.
So when Adele sings, “Never mind I’ll find someone like you,” the long “I” in “mind” becomes elongated, making it difficult to pronounce in a London clip. “If I say ‘aBOUT,’ you hear the stress on the second syllable,” Fioretta said. “But when you’re singing, that stress is reduced.”
5. It could also be that some performers with foreign accents deliberately choose to sound American to reach an American audience.
“It’s all about ‘performance practice,’ which means the musicians give the audience what is expected in a particular genre of music,” says Cindy Donnell, an associate professor of voice in the Virginia Commonwealth University Department of Music.
6. For example, contrast Keith Urban’s Australian accent, which comes across in his speaking voice…
7. …with the Southern twang he sings with in his music.
(Urban most likely sings in a twang to fit in with the rest of the American country canon.)
8. But sometimes you can hear singers’ foreign accents, like in a lot of songs by The Clash.
This is probably due to Joe Strummer’s vocal style, which takes more of a “normal speaking” approach to lyrics; or, as Mental Floss pointed out, British Invasion bands like The Kinks could also have intentionally kept their accents in order to lure in the American audiences they were trying to appeal to.