The A5 chip in the iPhone 4S has a special bit of tech that gives Siri improved voice recognition performance. It’s called Audience EarSmart noise reduction and it optimizes Siri performance on the handset.
Audience, Inc. revealed this when filing for a public offering last month, they said in an S1 filing “commencing in the three months ended December 31, 2011, Apple has integrated our processor IP in certain of its mobile phones.”
They also mention their processors and a processor custom made for Apple. They go into more detail in the full report, but the short of it is that their processor imitates the processing that occurs from the ear to the human brain. It works to understand the difference between background noise and the voice speaking directly to it. This is not only true with Siri, but it helps for clearer conversations.
Audience’s technology was also in the iPhone 4, something that iFixit discovered last year. It was a noise cancellation component located within the handset.
You can read a more detailed report at Apple Insider.