Inside Staples Center, the singer's performance earned loud applause. But to the Twitterverse watching at home, the pop and country superstar sang a little bit flat.

Swift was dancing in the footsteps of countless artists who have performed live at music's biggest night. Unlike Beyoncé at President Obama's inauguration last month, Swift had no choice: She had to sing and take her chances.
 

That's because the Grammys have a zero-tolerance policy for lip-syncing, requiring all performances be live.

"Since Milli Vanilli, the mandate has been made absolutely unequivocally," said Michael Abbott, the audio director who has helped coordinate the show's live performances for more than 20 years. "The Grammys only have live performances, no questions about it."

Grammy officials say the no lip-syncing edict came after pop and dance group Milli Vanilli was stripped of its 1990 best new artist award when the duo admitted that they did not use their actual voices on their album or in performances.

After R&B star Chris Brown's acrobatic dance performance at last year's Grammys, many wondered how he could possibly pull off those moves while singing on key.

Though the Grammys allow performers to use some special sound effects and track augmentation during their performances, Abbott insists viewers are hearing their actual voices and instruments.

As performances continue to become more elaborate, artists face new challenges to ensure the quality of their sounds, said Ilana Martin, a voice coach who has worked with artists such as P. Diddy and Alicia Keys.

Martin said the ideal physical setup for a vocal performance is standing at a microphone – such as country star Carrie Underwood's performance of her songs "Blown Away" and "Two Black Cadillacs" at Sunday night's show.

Artists known for their moves such as Usher and Pink are known to practice singing while running or jumping on trampolines to master singing while their bodies are bouncing, Martin said.

During his performance with rapper Wiz Khalifa at Sunday's Grammys, R&B singer Miguel sang while dashing down the aisle of the audience — and his crooning on "Adorn" didn't falter.

"If you've got the fire in your belly, and sing with your whole spirit," Martin said, "you're going to rock the performance."

wesley.lowery@latimes.com