As Fox prepares to raise the curtain Tuesday on the ninth season of its smash-hit singing competition, most of the intrigue has been focused beyond the stage — on the judges, the ratings, the voting procedures and the annual tinkering with the show’s format, which, at least to Fox and the show’s producers, never seems to be just right.

Since the end of the last season, of course, the producers have made one of the show’s biggest changes to date. Paula Abdul, who since the show’s beginning had nurtured contestants and played the role of nice judge to Simon Cowell’s mean one, is gone, replaced by Ellen DeGeneres, the talk-show host and comic. Ms. DeGeneres will not be seen until early February, however, when the taped “Hollywood round” of episodes, which are taking place this week in Los Angeles, whittle some 200 contestants down to 24 semifinalists. Guest judges — including Victoria Beckham, Avril Lavigne and Katy Perry — will fill the fourth spot at the judges’ table during the audition episodes.

If the addition last season of a fourth judge, Kara DioGuardi, upset the balance that gave the “Idol” judging panel an air of predictability, the arrival of Ms. DeGeneres is likely to be even more disruptive, not least because she might have a wit sharp enough to puncture the pontifications that often emanate from Mr. Cowell.

Mr. Cowell’s future too is in question. Though his contract expires after this season, he has at times said he expected to be with the show for much longer but, more recently, voiced his feeling that he had had enough of “Idol.” Last month his brother, a British radio journalist, reported that Mr. Cowell had decided to leave after this season, something that Mr. Cowell himself has not disputed.

What is certain is that he has been negotiating with Fox to bring to the United States his show “The X Factor,” a talent competition whose popularity exploded last year in Britain. Last week rumors flew around Hollywood that at the Television Critics Association meeting Monday in Pasadena, Calif., Fox would announce a deal to broadcast “The X Factor” beginning in 2011. Fox officials declined to comment on that last week.

Randy Jackson, the other judge who has been with the series since its beginning, said that all the chatter about whether Mr. Cowell would stay or go has been, at least, bothersome.

“In terms of the show I’m pretty sure it’s a distraction,” he told reporters in a conference call on Friday. “The rumors get so wild and crazy, I don’t know what to believe.”

Among the speculation was one story that had Mr. Cowell inviting Ms. Abdul to join him as a judge on “The X Factor.” Asked about the abundance of gossip about a potential competitor to “Idol” on the same network, Mr. Jackson said: “I really don’t know. Until I really hear it from him, I’m not going to believe anything.”

Fox has done little to tamp down speculation around “Idol,” perhaps hoping that the intrigue will help it accomplish something that it has not done since 2006: increase viewership.

Last year an average of 25 million people watched each episode of “American Idol,” according to Nielsen, down from 26.7 million a year earlier. That was the third straight year of decline, since the average audience peaked above 30 million in the fifth season.

Most of the decline has been among teenage viewers, according to Brad Adgate, a senior vice president for research at Horizon Media who has examined the “Idol” ratings in just about every way possible.

“It’s no longer as much of a buzzworthy show, particularly among teens and young adults, as it was several years ago,” he said in an interview. “Perhaps it’s a victim of its own success. It has become too mainstream, too popular.”

That means that contestants might be well served by brushing up on the oldies. Mr. Adgate noted that last year’s ratings among viewers ages 12 to 17 and adults ages 18 to 49 were the lowest since the inaugural season, while the show’s highest-rated demographic group was adults 35 to 64.

“It’s becoming your parents’ ‘American Idol,’ ” he said.

Not everyone buys that argument, least of all Fox. Its executives are quick to point out that the gap between “Idol” and whatever is the second-highest-rated show has grown steadily.

Nina Tassler, the president of CBS Entertainment, told reporters on Saturday that to her network “American Idol” was “still the Death Star.” While “NCIS,” the CBS series that is currently the most-watched show on television, has performed decently against “Idol” on Tuesday nights in recent years, “that show is still a force to be reckoned with,” she said.

The producers of “American Idol” have not been content to rest on their laurels. Two years ago they began to allow contestants to play instruments when they sang. Last year they expanded the semifinal round to 36 contestants from 24, a format that allowed the judges to give some of their favorites another chance to impress voters in a wild-card round before the field was narrowed to a final 13.

Exactly what the producers have planned for this season is a mystery, however. While the executive producers of the show have usually briefed reporters each year on plans for the coming season, this season’s briefing was canceled without explanation last week. (Fox executives, however, have said to expect just 24 semifinalists this year, no wild-card round and only 12 finalists, the typical number.)

It is not clear whether Fox will adjust voting procedures that drew criticism last season. Even as the audience has declined for several years, the number of votes cast each week has skyrocketed.

After last season’s finale some viewers admitted casting thousands of votes by text message, perhaps in violation of rules against using “technical enhancements” to cast blocs of votes. In Arkansas, the home of the eventual winner, Kris Allen, representatives of AT&T, an “Idol” sponsor, provided free phones and texting lessons at a party filled with Mr. Allen’s supporters.

While that might have helped Mr. Allen to victory, it has not helped him sell more records than last season’s runner-up, Adam Lambert. That, in the end, could indicate that who eventually wins might be the least compelling question around the new season of “American Idol.”