Despite music’s popularity on wireless devices, stereo Bluetooth remains a geek’s luxury.

Six years after its development began, the Bluetooth SIG’s Advanced Audio Distribution Profile (A2DP) is just beginning to find its way into wireless devices. The purpose of A2DP is to enable stereo output for wireless headphones. Yet all technologies have room for improvement, and A2DP’s weaknesses are highlighted by its exclusion from the most entertainment-centric, cutting-edge device of all – the Apple iPhone.

A2DP isn’t very popular even among tech geeks, but that is changing quickly. The realization generally goes like this: After spending hundreds of dollars for a high-end handset, a consumer takes home his new bounty, pairs it with a Bluetooth earpiece, and expects the same sound quality as from his MP3 player. It never arrives. The consumer hops onto Google, find a mobile blog or discussion forum, and discovers that he’s in A2DP limbo.

An Apple representative in Cupertino, Calif., declined to comment on A2DP, which according to most reports will not be part of the current iPhone wave of announcements focusing on a software development kit (SDK). Of course, a firmware upgrade could include A2DP at any time, along with other features conspicuously missing from the iPhone such as the basic ability to cut-and-paste. Indeed, Apple could add A2DP before this article reaches your mailbox, yet the question would still stand: Smartphones have been around since the 1990s, so why is stereo Bluetooth such a rare feature?

“A2DP is for all intents and purposes a geek’s luxury at this point. Really only in the last year has A2DP been in cell phones. It’s just not that obvious,” says Mark Pundsack, president of Wi-Gear, an accessory vendor in San Francisco.

Battery Drain
Most experts agree the major technical obstacle is battery life. Transmitting stereo audio wirelessly, regardless of the communications protocol, requires the transmitter to be switched on the entire time. On a smartphone, power is also constantly allocated for the telephony radio, for the screen or touchscreen, and for a heftier central processor than found in ordinary wireless phones. Including A2DP output could easily drain the talk time by 10% or more, Bluetooth SIG Executive Director Mike Foley says. There are also business reasons not to include it. High-end A2DP implementations often require an additional DSP chip, driving up the parts cost, and companies like Apple make several dollars for every third-party stereo adapter sold.

Foley calls out Apple in particular as the company which consumers expect to set the feature bar at a high level. “As hard to believe as it is, the iPhone does not enable stereo headphones … Supporting stereo for headphones, car stereos, portable speakers and home stereos is a simple extension,” he wrote, in a June 30, 2007, blog post, titled iDisappointment, on the Bluetooth SIG page – despite Apple’s membership in the organization.

“If the iPhone implements the standardized Bluetooth stereo profile, the device will work with headphones, cars, home stereos and portable speakers from any manufacturer. While this is great for the consumer, it isn’t as great for Apple’s bottom line. Apple may be under the impression that they can create an entire ecosystem of wireless peripherals for the iPhone and iPod in which they control by licensing the proprietary interface into the devices,” Foley continues. “I’ve asked Apple what the rationale was for not enabling more Bluetooth features in the iPhone, but as of yet, have not received a reply,” he says.

Interference
There has been industry speculation that interference between the telephone radio and the Bluetooth radio is another challenge to the rollout of A2DP 1.2, which is the newest version. Foley says that speculation is not true. “We probably have more Bluetooth devices per square foot in the country and we also run Wi-Fi and things like that, and we don’t see any issues,” he says, referring the SIG headquarters in Bellevue, Wash. “It’s been out there long enough. All these sorts of concerns don’t hold water any more,” he says.

A possible solution to the A2DP power problem is Wibree. Originally pushed by Nokia, Wibree became part of the Bluetooth portfolio last summer. It’s designed for ultra-low-power devices such as wristwatches and clock radios. That specification will be published in the first half of 2009, but handset makers would be in the minority of users for it, Foley says.

Sony and Qualcomm are among the companies that do include A2DP in headsets and phones. Motorola is another; its ROKR E8 is  one such phone, but like the iPhone, it does not have 3G networking, that being a power hog as well.

“In general, we found that the A2DP standard has been very well-defined for some time now. The technical challenges themselves are really not that substantial for implementing the technology. Certainly there are things from vendor to vendor that impact things such as battery life and audio quality to some degree,” adds David Favreau, senior director of product management at Qualcomm.

The minor controversy could abruptly end because of the recent trend in hands-free driving laws, says Steve Bellamy, president of the Stanford Mac User Group. “People are still quite used to using their earbuds,” he says. “They’ll probably want to have better music capability. It’s purely a matter of what’s the most important thing to do first.”