Audience researcher Quantcast is in the process of raising a $50 million third round funding, PE Hub reported, citing an unidentified source. A rep for the company could not be reached for comment. Estimated at a $300 pre-funding valuation, Quantcast has been evolving beyond its primary role as a web analytics company. Last week, the San Francisco company released its Quantcast Media Program, which offers targeted buying and selling according to marketers’ and publishers’ data on audience demos. The data is based on the insights Quantcast has gleaned from 10 million websites, blogs and videos. Also, yesterday WSJ ran a glowing profile of the company, based off its new service.

PE Hub said it wasn’t clear who the lead investors are on Quantcast’s prospective third round. While the report says the Quantcast has received term sheets, it’s also not apparent whether or not investors are meeting Quantcast’s desired funding amounts. Based on WSJ’s story quoting an enthusiastic NBC exec waxing over Quantcast’s service (and it is rolling out the media buying servcie across all NBC online properties), its media fund Peacock Equity could possibly be one of the potential investors.

In January 2008, Quantcast raised a large $20 million second round that was led by Founders Fund (Peter Thiel’s fund) and Polaris Venture Partners. The year before that, it secured $5.7 million in its first round from Founders Fund and Revolution Capital.

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