Pop singer Ashlee Simpson, appearing on NBC's "Today Show" this morning, denied that she was attempting to lip-sync on Saturday Night Live this past weekend, saying that what the audience heard instead of her voice was merely a recorded "backing track"--of the wrong song.

She said that had her voice not failed due to an acid reflux attack, she would have sung right along with the backing track, had it been the right song. It wasn't the right song because her drummer pushed the wrong button, she said.

She said all sorts of singers, including stars, use backup tracks when they are performing "live."

"Most artists on big shows do that," she said.

Asked whether she was surprised that the episode has created such a controversy, she said: "Yeah, because I am not anorexic. My boob didn't pop out. I am not on drugs. I had a bad performance and I got sick."

"Everybody makes mistakes," she told NBC's Katie Couric in a live interview, except that in this case, it was her band's drummer who made the mistake by pushing the wrong backup-track button.

The result was that while she mouthed the words to her new song "Autobiography," the audience heard a "backup track" of "Pieces of Me," which she had sung earlier in the show, also, she acknowledged, with a backing track.

When she realized what was happening, she did a funny dance -- described by Couric as a "hoedown" -- and walked off the stage.

"It was definitely upsetting and mortifying," said Simpson. "I get comments, like now, I'm like, Milli Vanilli. . . . I am always singing on any show I have ever done. Singing as hard as I can always. This was a situation where I was in trouble, like with my voice."

Simpson said she has been struggling with "severe acid reflux" for some time.

According to the American Gastroenterological Association, acid reflux (sometimes called "heartburn") is actually gastroesophageal reflux disease or GERD. It is a chronic condition, in which acid from the stomach flows upward into the esophagus. "The word reflux," according to the AGA Web site, "refers to the backward flow of stomach contents into the esophagus."

"My voice was in great shape" all during rehearsals, Simpson told Couric. "I was so ready to go. Saturday night came at six o'clock. I have severe acid reflux. It started acting up and I could not speak or talk. But most artists on big shows do that [sing to a backing track] and I had never done it once."

Were you "lip syncing" Couric asked directly.

"No," said Simpson. "I was singing with the track. Like on the first song. I was singing with the track but my voice was not strong enough to hold up the song alone. . . . "

Couric: "When you listen to someone performing live and they have a backing track, do you primarily hear the recording or the voice of the artist or does it depend?"

Simpson: "You hear both. The sound bites fade in and out depending on how your voice is. I have never done it before. . . . My drummer, who I love and adore, accidentally pressed the wrong button and did not set up the song. . . . "

Couric: "Before we go, where did you get the little hoe-down moves?"

Simpson: "I don't know. From Texas. I freaked out. . . .