Amazon.com (Nasdaq: AMZN) has quietly acquired speech-to-text software developer Yap, a move fueling speculation that the digital retail giant plans to build a speech recognition interface to rival Apple's (Nasdaq: AAPL) Siri personal assistant technology.

Although Amazon snapped up Yap in September, no public announcement has been made. The acquisition was first reported Wednesday by The Atlantic, which uncovered an SEC filing that doesn't even identify Amazon by name, but instead states that Yap merged with a company called Dion Acquisition Sub that is headquartered at 410 Terry Avenue in Seattle, Wash., the address of Amazon's legal services team.

Yap's voice recognition software transcribes dialogue extending up to 10 hours. Founded in 2006 by Igor Jablakov, who previously worked on speech recognition technologies at IBM, Yap raised a $6.5 million Series A financing round in mid-2008 -- last month, the firm discontinued its Yap Voicemail application.

The Yap acquisition could help Amazon to integrate speech recognition services into its mobile shopping applications and Kindle e-reader solutions, simplifying search for products and text. Although Amazon's forthcoming Kindle Fire tablet does not include a microphone, the smartphones running its various applications do.

Apple's Siri enables iPhone 4S users to employ natural spoken language to access and perform device tasks like mobile search, messaging and contacts. The technology (acquired by Apple in April 2010) essentially applies search algorithms to translate users' verbal search queries and commands into web searches. Apple senior vice president of worldwide product marketing Phil Schiller has described Siri as an "intelligent assistant that helps you get things done just by asking."

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