iPhone 4S A5 Processor Packs Custom Siri "Ears" Chip

Apple's refusal to put its Siri voice control system on the iPhone 4 is not a shameless play to persuade users to upgrade to the 4S, it's suggested, but a limitation of the Apple A5 chip found inside the newest iOS smartphone. The A5, Linley Group analyst Linley Gwennap says, was always too large simply to accommodate two Cortex A9 CPUs and a GPU, CNET reports; the extra bulk is to house an on-chip noise-reduction system sourced from specialists Audience, which revealed its deal with Apple last month.

"Apple has integrated our processor IP in certain of its mobile phones" Audience confirmed in its IPO documentation last month. Based on the company's EarSmart technology, it allows phones to use effective background noise cancellation even when the microphone is held at arm's reach, rather than when it's near the user's mouth.

Audience doesn't detail its "custom processor for Apple" but the volume inclusion timescale – Q4 of 2011 – fits in with the launch of the iPhone 4S. EarSmart models the human brain, using two microphones and custom DSP to filter out background sound.

It's that ability – present in the iPhone 4S but missing from the iPhone 4 and earlier devices – which limits Siri's backward-compatibility, Gwennap argues. As we've seen from unofficial hacks, the A4 chip powering the iPhone 4 is capable of running Siri on a power level; it seems the stumbling block is whether Siri can actually hear you properly.

Apple is a licensee of Audience's next-gen noise reduction tech, though the company points out that the iPhone maker is under no obligation to actually use it. Still, that could appear in the Apple A6 chipset, expected to be at the heart of the iPad 3