SIOUX CITY, Iowa - President Obama today raised expectations for his convention acceptance speech in Charlotte, N.C., telling voters here that he would provide a more detailed and effective "path forward" for the economy than his rival, GOP nominee Mitt Romney.

Giving what he called a "recap" of the Republican Convention of the past week, Obama said Romney fashioned himself as possessing a powerful "secret to creating jobs and growing the economy."

But Obama said viewers of the convention would have been at a loss to understand exactly "what they were going to do. "

"When Gov. Romney had his chance to let you in on his 'secret sauce,' he didn't offer you a single new idea. It was just a retread of the same old policies that have been sticking it to the middle class for years," Obama told the crowd of 2,800 gathered on the campus quad at Morningside College.

"They spent less time talking about their plan than just about anything else. Not just because they know you don't like it. The truth is if I had their plan I wouldn't talk about it a lot either. And they know you're not going to buy it because we tried it, you saw what happened, you lived through it, and you don't want to repeat it," he said.

A spokesman for Romney did not immediately respond to ABC News' request for comment on Obama's criticism.

The president hinted at his message to be delivered Thursday in a nationally televised speech before tens of thousands at the outdoor Bank of America Stadium, but did not offer many details of his own.

"I will offer you what I believe is a better path forward," he said. "A path that will grow this economy and create more good jobs and strengthen our idle class and create ladders for everybody who's working hard to get into the middle class. And the good news is you're going to get to choose."