The Bluetooth standard defines different types of communication for different applications. These are called Bluetooth profiles. There are three relevant profiles for the transmission of audio signals:
The Advanced Audio Distribution Profile is used to stream stereo signals in HiFi quality. The standard SBC Codec allows sampling rates up to 48 kHz. AAC or APTx codecs are used optionally.
There is an A2DP Source and an A2DP Sink profile.
- Typical A2DP Source devices are mobile phones, tablets or TVs.
- Typical A2DP Sink devices are loudspeakers, headsets, earbuds or a car radio
The HeadSet Profile is used for bi-directional voice transmission. The SCO Codec provides a sampling rate of 8 kHz. This corresponds to the bandwidth of a conventional telephone connection. There is a HSP Gateway and a HSP Client profile.
- The typical HSP Gateway device is a mobile phone.
- Typical HSP Client devices are headsets or earbuds.
The HandsFree Profile is also used for bi-directional voice transmission, but offers some extended properties over the HSP profile. As examples, there is the possibility to transfer the address book of the gateway device to the client, and the MSBC codec provides a 16kHz sampling rate for improved speech quality (e.g. for Skype calls).
A HFP Gateway and HFP Client is identified.
- Typical HFP Gateway devices are mobile phones or computers
- Typical HFP Client devices are car radios, headsets or earbuds.
Many devices support all three of these profiles. The appropriate profile is selected automatically depending on the application.