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Apple A5 Mystery Solved

February 3, 2012

Author: Linley Gwennap

Our previous coverage of Apple’s custom-design A5 processor pointed out that the die size of the processor is much larger than that of competing application processors. 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. We speculated that Apple included some custom logic to improve the performance of its products.

A recent S-1 filing from Audience confirmed this speculation and explains exactly what that custom logic does. For those unfamiliar with the company, Audience has developed impressive technology that removes most or all of the background noise when someone places a cell-phone call from a restaurant, airport, or other noisy location. The company initially offered this technology in a small chip, which Apple included in the iPhone 4, generating sizable revenue for the startup.

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. This technology is critical for the new phone because not only does it improve call quality, it blocks out background noise when users provide voice commands to Siri, the intelligent assistant built into the iPhone 4S. Without this noise reduction, Siri would be unusable even with a modest amount of background noise.

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 “farfield speech,” which means holding the device at arm’s length rather than directly in front of the mouth.

According to the S-1 filing, Apple has also licensed the Audience technology for a “new generation of processor IP,” which we assume means the forthcoming A6 processor that will appear in the iPad 3 and iPhone 5. Because the A6 design (tape out) was completed months ago, any licensing deal for that chip must already be complete.

Why Apple has not simply purchased Audience is unclear. An acquisition would prevent Audience’s other major customer, Samsung, from using the technology to compete with Apple. The company may be hedging its bets, as it could switch to Qualcomm’s Fluence noise-reduction technology in the future. In the meantime, Audience is moving forward with its IPO, based on design wins at the two leading smartphone vendors.

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