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 responded a query that Linley crew analyst Linley Gwennap had about the A5 chip that powers the iPhone 4S: why is it so massive? larger processors are more expensive and can eat more energy, and chip designers attempt to trim each final sq. 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 within the 3 months ended December 31, 2011, Apple has built-in our processor IP in sure of its cell phones. Pursuant to our settlement, this OEM [original equipment manufacturer] pays us a royalty, on a quarterly basis, for the use of our processor IP for all cellphones by which it’s used.

target audience’s 2d-generation era, which introduced its some distance-box noise-reduction era, started shipping in 2011, the corporate stated in its filing. The iPhone 4 arrived in 2010, prior to a long way-field was once incorporated.

a third generation of target audience’s noise-reduction technology is at the method, too, and Apple is a licensee, despite the fact that target audience suggested that Apple isn’t contractually required to use it. where it could most likely be integrated is inside the purported A6 anticipated to power the purported iPad three.

“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.

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 will get more difficult while individuals are preserving their telephones further from their mouths, as steadily occurs while videoconferencing, making arms-free calls in a car, and issuing voice instructions equivalent to with the Siri gadget.

“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.