Given the joy which Apple‘s iPhone 4S users have been greeting Siri there’s been some speculation as to why it’s not been released as an upgrade to the iPhone 4. The cynic’s answer, that the joy at getting Siri might spark an upgrade to an iPhone 4S, seems not to be the reason.

It is actually possible to be too cynical, something which comes as a slight surprise.

The answer is that the hardware won’t be able to support it properly. It’s not about processing power, bandwidth or memory. It’s about the technology in the iPhone 4S which dampens background noise and which the earlier iPhone 4 doesn’t contain.

There’s a nice explanation of it here:

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.

I take it to mean that you could in fact put Siri on an iPhone 4 (which would explain many of those stories about hacks doing just that) but it wouldn’t work very well. And as we know, Apple just hates anything that doesn’t work well. Thus no release as an upgrade for Siri on the iPhone 4.