Apple's A5 System on a Chip incorporates dedicated noise reduction circuitry by Audience, Inc., which optimizes the performance of Siri voice recognition on iPhone 4S.



From Apple Insider:

When Audience filed for an initial public offering last month, it revealed that "commencing in the three months ended December 31, 2011, Apple has integrated our processor IP in certain of its mobile phones," in a S1 filing outlining the startup's potential risk factors for investors.

The firm also made reference to its own "first generation of processors, the A1026, the A1028 and a custom processor for Apple," and stated, "we began shipping our first generation of voice processors in 2008, our second generation of earSmart voice and audio processors in 2011 and as of December 31, 2011, had sold over 135 million processors worldwide."

  Apple iPhone 4S A5 chip incorporates Audience EarSmart noise reduction tech for Siri