When Apple announced that its new Siri assistant would only be available on the iPhone 4S last October, it caused quite a commotion in the iOS community. It meant that millions of iOS users, even those who recently purchased new devices, would have to go without the feature.

We’ve heard a couple of theories on why Apple chose to make Siri 4S-only, including the need for a solid selling point for its new handset, and the fact that it’s still in beta. But according to a recent CNET report, it’s all about the processor…

Stephen Shankland of CNET reports:

“Apple’s A5 processor includes noise-reduction circuitry licensed from a start-up called Audience, and a chip analyst believes that fact resolves an iPhone 4S mystery and explains why the iPhone 4 lacks the Siri voice-control system

Audience revealed details of its Apple partnership in January, when it filed paperwork for an initial public offering (IPO) of stock. Teardown work from iFixit and Chipworks revealed a dedicated Audience chip in the iPhone 4, but the iPhone 4S integrates Audience’s “EarSmart” technology directly into the A5 processor, the company’s S-1 filling said.”

While Apple’s iPhone 4 also contains Audience’s noise reduction technology, it only works when the handset is held up near the speaker’s mouth. The “EarSmart” tech built into the A5 processor which is in the iPhone 4S, however, can handle ‘fair-field speech,’ meaning it can pickup sound from a couple of feet away.

This doesn’t mean that the iPhone 4 isn’t capable of running Siri — we know for a fact it is. It just sounds like this was another factor that led to Apple’s decision to keep the assistant a 4S-only feature. And another reason why we probably won’t see Siri opened up to older devices in the future.

[MacStories]