Bluetooth is a short-range wireless radio frequency communication technology which operates in Industrial Scientific Medical (ISM) band at 2.4 GHz. According to the Bluetooth Specification and Profiles made by Bluetooth Special Interest Group (SIG), the Bluetooth basic network structure is a Piconet composed of one master unit and up to seven slave units. The master unit communicates with its slave units by TDMA. By integrating Bluetooth communication module into each device, diverse kind of the devices can be connected in low cost. Bluetooth Asynchronous Connection-Less Link and Synchronous Connection-Oriented Link can be established among Bluetooth units by using globally unique Bluetooth Unit Address, so as to transmit character data and audio data among them. The functions of one unit may be provided to another unit by way of Bluetooth service, so one unit can provide multiple services simultaneously, and Users can choose some of the services to establish connection according to their needs.
As a short-range wireless radio frequency communication technology, the aim of Bluetooth is to take place of wired connections. It provides SCO/eSCO link to transmit real-time voice signals with low sampling frequency, where users can conveniently receive or dial phones by handsets (Headset, Hands Free, Cordless Telephone Profile); at the same time, it uses ACL link to transmit high quality audio encoding data (MP3, SBC format), so users can conveniently listen to the music, etc.(Bluetooth AV Profile)
In a computer operating system, Bluetooth soundcard audio unit should be incorporated into the operating system in order to implement the support to Bluetooth audio application. The Bluetooth audio application in operating system outputs audio data to Bluetooth soundcard audio unit, and the Bluetooth soundcard audio unit converts the audio data and transmits them to remote Bluetooth unit via Bluetooth audio connection. Following the reverse direction, the system receives audio data from remote Bluetooth unit via Bluetooth audio connection and the said audio data is reported to Bluetooth soundcard audio unit. And then the said audio data is converted in the Bluetooth soundcard unit and reported to Bluetooth audio application in the operating system.
Currently, only one Bluetooth soundcard audio unit is added into the operating system of computers in the scheme for supporting Bluetooth audio Profile (application). Any Bluetooth audio applications, like high quality Bluetooth audio application and low quality Bluetooth audio application are all supported via the Bluetooth soundcard audio unit.
One disadvantage of the scheme is that the operating system can only support one Bluetooth audio application simultaneously because there is only one Bluetooth soundcard audio unit. Even if multiple Bluetooth audio applications can be made to use the same Bluetooth soundcard audio unit, the audio data from the multiple Bluetooth audio applications shall be mixed together, resulting in unacceptable usage effects. However, in practical applications, multiple Bluetooth audio applications often need to be connected at the same time, for example, using an ordinary Bluetooth earphone to establish Bluetooth call based on SCO/eSCO link while playing songs on another stereo Bluetooth earphone.
Another disadvantage of the scheme is that it is impossible to achieve optimal matching between Bluetooth audio applications and formats of audio data supported by the Bluetooth audio connection established, due to the use of single Bluetooth soundcard audio unit. Because Bluetooth soundcard audio unit reports the supported sampling frequency (from 8 KHz to 44.1 KHz and above) and sound track mode (single sound track and dual (or stereo) sound track) to the system and to audio application via system standard interface, so when the Bluetooth soundcard audio unit supports both high quality Bluetooth audio application and low quality Bluetooth audio application, the Bluetooth soundcard audio unit will report to the system and audio application that the supported sampling frequency will be from 8 KHz to 44 KHz and above, and that the sound track modes will include single sound track and dual sound track. Since audio applications usually employ the highest sampling frequency and the optimal dual sound track mode of the soundcard, the Bluetooth audio data output by the lower layer interface of Bluetooth soundcard audio unit corresponds with higher sampling frequency. Thus, for low quality Bluetooth audio applications, the higher sampling frequency/sound track mode of the audio data output by Bluetooth soundcard audio unit may not match the lower sampling frequency/sound track mode of the data from the low quality Bluetooth audio connection that has been established. And the format conversion for the Bluetooth audio data output by the Bluetooth soundcard audio unit is needed, namely to convert the high sampling frequency/dual sound track into 8 KHz (16 KHz)/single sound track corresponding to Bluetooth SCO/eSCO link, which will increase the conversion burden of the system.