Bluetooth profile comparison

A comparison between using A2DP or SCO profiles.

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Last updated a day ago

The Bluetooth API provides implementations for the following Bluetooth profiles that are relevant to Vivox:

Bluetooth A2DP

The Advanced Audio Distribution Profile (A2DP) profile defines how high-quality audio can be streamed from one device to another over a Bluetooth connection. It defines how multimedia audio can be streamed from one device to another over a Bluetooth connection (it is also called Bluetooth Audio Streaming). For example, music can be streamed from a mobile phone to a wireless headset, hearing aid/cochlear implant streamer, or car audio. A2DP is uni-directional. There is no support for capturing audio on a Bluetooth device at the same time as rendering audio.

Bluetooth SCO(HFP)

The Bluetooth Hands-Free Profile (HFP) allows the Bluetooth device to make and receive voice calls via a connected handset. Synchronous Connection-Oriented (SCO) is the type of radio link used for voice data.

Tradeoffs of using SCO or A2DP

A2DP audio is rendered on the Bluetooth headset. Because there’s no support for capture and render at the same time using this profile, most handsets will capture audio from the microphone on the phone. The rendered audio is high quality and stereo. Game audio will remain high quality and will play through the headset along with voice. SCO voice audio is both rendered and captured from the Bluetooth device. The rendered audio is of lower quality (similar to that of a standard phone call) and mono. Depending on the Android device, game audio will either:

Play as low-quality and mono audio through the Bluetooth headset along with voice. Or,
Play from the phone with standard quality.

Latency

A2DP tends to have more latency than SCO, but not too much more (100 - 200 ms). The extra audio quality of A2DP is notable. Because of Bluetooth’s inherent low-power requirements, low latency, two-way communication is provided through SCO by reducing the sample rate and the number of channels rendered which leaves bandwidth for a microphone channel.

Implications of using the handset microphone

With A2DP, having the microphone on the handset means that hand noises and screen taps may be audible, so extra rustling and thumping is expected. The hands holding the device can cause muffling of captured audio because they occlude the microphone or completely cover it. With SCO the audio is captured from the Bluetooth device, so no hand noise is typically captured. Another concern is that the handset can be put down and end up far from the user. With A2DP, as the user moves away from the handset, they will get further from the microphone, and be more difficult to capture. With SCO, they can still be heard clearly no matter how far the user is from their phone (within Bluetooth range).

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