Bluetooth – A2DP explained.

Bluetooth – A2DP explained.

How the new, improved Bluetooth will deliver quality audio.

Bluetooth is a ubiquitous wireless technology that has gained a lot of followers because it does its job with minimal fuss. Between its popularity and the demand for wireless headphones, Bluetooth is about to be extended to carry high quality stereo audio signals with the introduction of A2DP -- Advanced Audio Distribution Profile.

Low quality audio was necessary in the first version of Bluetooth for reliable transmission to mobile phone headsets, because that market was rightly picked to drive the uptake of the technology. Now, consumer demand for wireless everything has meant high quality wireless audio has to be provided, and because you can’t change the reliable, low quality handset profile in Bluetooth, the A2DP profile has been created to compliment it by providing the bandwidth to send high quality audio.

This is what will power the next wave of Bluetooth headphones, and is being called Stereo Bluetooth by Motorola to avoid consumer confusion. In essence, Bluetooth’s available bandwidth is divided between two layers, a data layer and a voice layer. Mobile phone headsets use the voice layer -- a small amount of dedicated bandwidth. All other Bluetooth communication happens through the much wider data layer. A2DP sets aside a section of the data layer and sends high quality audio through it.

Behind the Scenes
Mobile phone headsets have a throughput of only 64kbps, which is a limitation of the voice layer. Although this means rubbish sound quality (which is nonetheless good enough for mobile phones) the upshot is that there is less chance of interference. This dedicated, bandwidth-limited voice channel works well for voice transmission but makes music sound like it’s being picked up through an AM radio attached to a tin can with some string. Even though three 64Kbps connections can be used simultaneously, more audio flexibility is needed.

The remaining 723Kbps of bandwidth is called the data layer, and provides all other Bluetooth functionality. A2DP simply carves off a chunk of the data layer, then streams high bit rate audio through it. The data layer also provides services like synchronization, image transfer, remote control and network access. The bandwidth is shared by all these services, so if you are streaming audio and trying to do other things, you may get dropouts. The uptake of Bluetooth 2, with 3Mb/s of bandwidth as opposed to 1Mb/s will avoid this problem.

Although many newer devices will support A2DP out of the box, using it natively on a computer without a dongle may be a problem, and one entirely dependant on your Bluetooth adapter. Windows XP doesn’t support Bluetooth headsets natively, let alone A2DP headphones. It leaves that task up to your Bluetooth hardware’s driver, which may not yet support A2DP. If you can’t get a driver update to enable A2DP, you can use a dongle to get on the bandwagon, which both Blue Ant and Motorola have already started producing.

Using it
Just because the audio is being routed through a wider data path doesn’t mean that the other benefits of Bluetooth have to be abandoned. The modular nature of Bluetooth means that the control profile, which is used to accept calls in headsets, can be used to play, pause, stop and shuffle through tracks on the client. Remapping controls away from the host device and onto the headphones has a certain appeal. It’s functionality made funky and lazy.

Bluetooth has high expectations to live up to due the accessorisation it has brought to technology. Consumers are demanding wireless music playback from MP3 players, and since the voice profile won’t let headsets deliver it to them, A2DP has fudged the underlying rules of Bluetooth audio transmission to let them.

Read the Blue Ant X5 Stereo Bluetooth headset review here.

Read the Bluesonic Bluetooth portable speakers review here.

Read the Motorola/Oakley O Rokr sunglasses review here.

Read the Motorola Bluetooth DJ Headphones review here.

Read the Motorola Bluetooth Stereo Gateway review here.

Read the Plantronics Pulsar 590A review here.


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