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Why Apple's A5 is so big--and iPhone 4 won't get Siri

Noise-reduction technology from a start-up called Audience accounts for the size of the iPhone 4S chip and keeps Siri off the iPhone 4, analyst Linley Gwennap concludes.

Stephen Shankland principal writer
Stephen Shankland has been a reporter at CNET since 1998 and writes about processors, digital photography, AI, quantum computing, computer science, materials science, supercomputers, drones, browsers, 3D printing, USB, and new computing technology in general. He has a soft spot in his heart for standards groups and I/O interfaces. His first big scoop was about radioactive cat poop.
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A diagram of Audience's sales pitch: identify the speaker's voice and isolate it from background noise.
A diagram of Audience's sales pitch: identify the speaker's voice and isolate it from background noise. Audience

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 filing said.

The details answered a question that Linley Group analyst Linley Gwennap had about the A5 chip that powers the iPhone 4S: why is it so big? Larger processors are more expensive and can consume more power, and chip designers strive to trim every last square millimeter from their designs.

"Even after accounting for the dual Cortex-A9 CPUs and the large GPU that provides the A5 with industry-leading 3D graphics performance, the remaining die area seems too large for the usual mundane housekeeping logic," Gwennap said in a report yesterday. "To reduce system cost and eliminate the extra package required for the Audience chip, Apple cut a deal to integrate the noise-reduction technology directly into its A5 processor, which appears in the iPhone 4S."

Audience also said in its filing that its iPhone 4-era technology was good only when the phone was held near the speaker's mouth. Audience's noise-reduction technology built into the iPhone 4S is better, though.

"This situation helps explain why Apple does not offer Siri as a software upgrade on the iPhone 4. Although the older phone includes an Audience chip, the company has since improved its technology to handle 'far-field speech,' which means holding the device at arm's length rather than directly in front of the mouth," Gwennap said.

Siri support has been a contentious issue for some owners of earlier iPhones. Hacks to bring Siri to older iPhones generally require technically complicated measures.

Audience said in its filing that its partnership to license its noise-reduction intellectual property (IP) began bearing fruit in the last quarter of 2011:

Commencing in the three months ended December 31, 2011, Apple has integrated our processor IP in certain of its mobile phones. Pursuant to our agreement, this OEM [original equipment manufacturer] will pay us a royalty, on a quarterly basis, for the use of our processor IP for all mobile phones in which it is used.

Audience's second-generation technology, which introduced its far-field noise-reduction technology, began shipping in 2011, the company said in its filing. The iPhone 4 arrived in 2010, before far-field was included.

A third generation of Audience's noise-reduction technology is on the way, too, and Apple is a licensee, though Audience cautioned that Apple isn't contractually required to use it. Where it would likely be integrated is within the purported A6 expected to power the purported iPad 3.

"We have granted a similar license to this OEM for a new generation of processor IP; however, this OEM is not obligated to incorporate our processor IP into any of its current or future mobile devices," Audience said.

A diagram of Audience's technology for stripping out unwanted noise from an audio signal.
A diagram of Audience's technology for stripping out unwanted noise from an audio signal. Audience

Apple isn't the only customer, though it's certainly the most prestigious. Other customers include HTC, LG, Pantech, Samsung, Sharp, and Sony, Audience said, for products such as Samsung's Galaxy S II, HTC's Titan, and Sony's Tablet S.

The Apple partnership has been lucrative for Audience, though the company didn't break out specific numbers.

"Foxconn, one of Apple's CMs [contract manufacturers], accounted for 81 percent and 70 percent of our total revenue in 2010 and the nine months ended September 30, 2011, respectively," Audience said. The 2010 revenue was $47.9 million, with a net income of $4.8 million, the company's first profitable year. For the first three quarters of 2011 revenue was $79.7 million with net income of $13.9 million.

EarSmart uses a digital signal processor to try to remove background noise and secondary voices so phone calls sound better when people are in restaurants, trains, or other noisy environments.

"Imitating the complex processing that occurs from the inner ear to the brain, Audience's intelligent EarSmart technology distinguishes and interprets sounds as people do naturally," the company says of its technology. "In a mobile device, the earSmart processor effectively isolates and enhances the primary voice signal and suppresses surrounding noise--for both transmit and receive--to enable clear conversations nearly anywhere."

Screening out noise gets harder when people are holding their phones farther from their mouths, as often happens while videoconferencing, making hands-free calls in a car, and issuing voice commands such as with the Siri system.

"Far-field uses are more vulnerable to background noise interference and poor voice quality given the speaker's distance from the device," Audience said.

In other words, without the latest Audience technology, Siri can't hear you so well.

Audience's noise-reduction technology is in several phones, including many from Samsung.
Audience's noise-reduction technology is in several phones, including many from Samsung. Audience