A Quick Road Map Through the Modern Maze of Bluetooth

A Primer and Perspective on Bluetooth, Wireless Audio and Remote Control. A basic fact about Bluetooth and similar standards is that their ultimate purpose in life is to promote compatibility between devices made by different manufacturers. At its essence, Bluetooth is about standardization of short-range wireless data exchange. The A2DP profile is about CD-quality stereo audio. The AVRCP profile is about remote control of audio/video devices. There is also an intercom profile, which can be used for rider-passenger intercom, but if I said more about that, this wouldn't be a primer.

iPod accessories that broadcast the audio to your FM radio are highly popular. Many of them also provide remote control of the iPod, and they demonstrate that you don't have to use Bluetooth for remote control. More recently, a different sort of iPod accessory has started to gain popularity. Instead of broadcasting the audio to an FM radio, it uses the Bluetooth A2DP profile to transmit the audio to a Bluetooth-enabled stereo headset. As with the FM radio gadgets, the Bluetooth accessories connect to the iPod at the docking port, in order to provide remote control of the iPod. Because these devices are designed around Bluetooth, they naturally use the AVRCP profile for remote control. These devices are great, but I find one very significant drawback to them: because the A2DP audio transmitter is integrated with the AVRCP remote control receiver, the integrated unit connects to the iPod at its docking port, and you end up with an A2DP transmitter that won't work with anything else, i.e., anything other than the iPod.

The A2DP transmitter that I use (Jabra A120s) works with any audio source that provides a standard 3.5mm headphone jack. It is smaller than most key fobs, and has a 3.5 mm stereo headphone plug dangling from a short length of coiled cord. You have to use care when setting the volume level at the source because this transmitter doesn't have automatic gain control, and its A/D converter has a ceiling, which, if exceeded, will result in horrendous distortion.

If you are considering one of the new Bluetooth helmets, and if you want to listen to music, you of course want to make certain it supports the A2DP profile. But if you expect to be able to hear the music, you'll want to use earphones that fit snugly into your ear canal. The best designs, in my opinion, are the A2DP receivers that allow you to use your own headphones, i.e., the ones that provide a 3.5 mm stereo headphone jack, in lieu of headphones that are wired directly and permanently to the receiver module. The module itself either clips to your shirt pocket or hangs from a neck lanyard. At least two such devices are presently available, and both of them support cell phone use as well as A2DP. Anyone who anticipates making phone calls while wearing a helmet (…) should pay attention to whether the microphone arrangement will accommodate the need to hook-n-loop the mic into the chin bar after putting on the helmet. The Jabra model has a microphone located in the module along with the buttons. The other one, from Satechi, has that, but also offers the option of using the included earphones, which have an in-line mic that overrides the mic in the main module. That one also happens to be unusually rugged, it doesn't exhibit any erratic behaviors, and its power gain is truly impressive.

Even though both of these A2DP receivers use AVRCP for remote control, that capability will not likely be useful unless you have a cell phone that doubles as your MP3 player, or unless your A2DP transmitter is iPod-specific, etc. If your A2DP transmitter is like mine and connects to the audio source via a 3.5 mm stereo headphone jack, and if you want to add remote control functionality for the iPod, there are dedicated iPod remote controls, such as the iJet remote, that do not concern themselves with audio transmission (or with Bluetooth). You can attach the remote transmitter (the part with the buttons) to the top of your tank bag, and instead of awkward, multi-purpose buttons, the button layout emulates the familiar and intuitive iPod layout.

— By Tom Barber, used with permission.