About Bluetooth Audio Protocols In Mac OSX and iOS


A2DP's Importance For Stereo Audio

It's important to realize in Bluetooth audio's early days a single, monophonic headset for cell-phone use was the most common product to first appear. The frequency response was quite limited and designed for the more limited frequency range optimized for human voice. The notion of streaming high-fidelity stereo audio wasn't in the original Bluetooth specification; that came a few years later with the introduction of A2DP protocol.

Advanced Audio Distribution Profile (A2DP) defines how higher quality audio (stereo or mono) can be streamed from one device to another over a Bluetooth connection; i.e. music streamed from a mobile phone or tablet to a wireless headset or car audio. The term 'HIGHER'-quality is important. The stereo audio streams created in Bluetooth codecs are still compressed and not audiophile quaility. That's why we see things like true wireless speaker systems using RF signals or, like Apple AirPlay technology using the higher-bandwidth of a 802.11 WiFi connection to deliver higher-quality audio at far greater distances than Bluetooth allows.

A2DP was initially used in conjunction with an intermediate Bluetooth transceiver that connects to a standard audio output jack, encoded the incoming audio to a Bluetooth-friendly format, then sending the signal wirelessly to Bluetooth headphones that decode and play the audio. External Bluetooth iPod Dock adapters are an example of this. There are also standalone Bluetooth transmitter/receivers that feature connectors for you to add Bluetooth stereo reception to your home stereo receiver for high-wattage, hi-fidelity playback.

1-Piece Bluetooth headsets often come with a microphone and support for the MONOPHONIC Headset (HSP), Hands-Free (HFP) and Audio/Video Remote Control (AVRCP) profiles supporting things like cell-phone call management, acting as a speaker-phone. There are select over-the-ear headsets that support a second earpiece on a short wire that can deliver A2DP stereo for those who wan't minimal weight for phone calls, but higher quality for music listening.

A2DP is designed to transfer a uni-directional 2-channel STEREO audio stream at a much higher quality than for voice, such as music from a Bluetooth enabled cell-phone, MP3 player - to a headset or Bluetooth hands-free car receiver. This profile relies on AVDTP and GAVDP. It includes mandatory support for the low complexity SBC codec (not to be confused with Bluetooth's voice-signal codecs such as CVSDM), and supports optionally: MPEG-1 , MPEG-2, MPEG-4, AAC, and ATRAC audio formats needed for truly high quality stereo audio.

Mac OS X: As of version 10.5 Lepoard and later native support for A2DP on Bluetooth-equipped Macs is standard. OSX Version 10.4 does not natively support A2DP, but software like the Softick Audio Gateway for Mac also supports A2DP. The iPhone variant of OS X now supports A2DP, but only in version 3.0. So - more recent versions of iOS4 the 3G iPhone, WiFi iPad and 3GS iPad tablet support Bluetooth stereo audio input and output as well.

Bluetooth Uses For Your Mac

Consumers seem to LOVE wireless in any gadget that supports it. But Bluetooth is finding much wider uses than headsets, wirelss speakers, keyboards and mice. There's many other computing applications that need to transfer small files or data at close range:

+ Wireless control of and communication between a mobile phone and a hands-free headset.

+ Wireless networking between PCs in a confined space and where little bandwidth is required.

+ Wireless communication with PC I/O devices, the most common being a mouse, keyboard and printer.

+ Transfer of files, contact details, calendar appointments, and reminders between devices with OBEX.

+ Test equipment, GPS receivers, medical equipment, bar code scanners, and traffic control devices.

+ For remote controllers where infrared was traditionally used.

+ Low bandwidth applications where higher bandwidth is not required and cable-free connection desired.

+ Internet access on personal computers or PDAs using a data-capable mobile phone as a modem.

The Bluetooth Standard Evolves

Bluetooth (now at version 4.0) is an extensible and ever evolving audio standard that is steadily improving. Better audio codecs, better transmissio and reception range, data stream error recovery, multiple device pairing support, and more.