Bluetooth Low Energy Audio

In this blogpost I will give a brief overview of the new Bluetooth Low Energy (BLE) Audio features enabled by the recently released Bluetooth 5.2 Core Specification.

Previous BLE blog posts

We have previously written two blogposts containing information about BLE and the use cases enabled by it. Go read them to get the background of BLE and the state of it up until Bluetooth 5.1.

Adding audio to Bluetooth LE

By adding the functionality to stream audio using the Bluetooth Low Energy radio the Bluetooth SIG allows audio streaming for less power consuming devices with hearing aids as the main focus. Some hearing aids have since before been running Bluetooth but in those cases often using external hardware or proprietary protocols and profiles. Now the interoperability and ease of implementing has been greatly improved.

Other than improving Bluetooth audio in hearing aids there are multiple other use cases for the new LE Audio:

  • Better support for “True Wireless” allowing separate streams to each device (e.g. right and left ear). Previously this required proprietary solutions or only one of the earbuds being connected to the audio source (phone) which in turn would relay the audio packages to other earbud.
  • Allowing more Bluetooth sinks (headphones) to be connected to one source at once, e.g. letting you share the music you listen to with a friend.
  • Expanding the already existing broadcasting functionality (see Erik’s post about BLE) with also being able to broadcast audio streams. This could be used for traffic announcements in a train station, guiding tours at museums and a lot of other use cases!

LE Isochronous Channels

The new features described above are solved largely by a new addition to the Core Specification called Isochronous Channels. The way these channels are specified allows for multiple time synchronized Isochronous (audio) Streams within what is called an Isochronous Group. This makes sure that e.g. the correct audio packets are rendered at the correct times and discards packets which are no longer valid.

Connected Isochronous Streams

Variants for both Connected and Broadcasted Isochronous Streams/Groups have been added to the specification, to allow for all the new kinds of functionality for LE Audio. In the image above the arrows visualizing data directions are bi-directional between the master and the slaves, which is true only for Connected Isochronous Stream. Compare to the uni-directional arrows in the image for Broadcast Isochronous Group/Streams below:

Broadcast Isochronous Streams

For implementation details of the Isochronous Streams and Groups, refer to the Core Specification linked to at the bottom of this post.

New audio codec: LC3

Bluetooth LE Audio will use a new codec called LC3 (Low Complexity Communication Codec). According to tests performed by Bluetooth SIG, the new codec perform better audio quality at lower data rates than the current standard audio codec for Bluetooth BR/EDR called SBC. The promising test results would allow for using a lower bitrate while keeping the audio quality. A lower bitrate means less data sent and received using the radio enabling a lower power consumption.

See graph below for comparison in audio quality between LC3 and SBC from the study done by Bluetooth SIG. The rating is based on ITU-R BS.1116-3. The vertical numbers indicate the perceived difference in audio quality compared to the original source:

  • 5: “Imperceptible”
  • 4: “Perceptible, but not annoying”
  • 3: “Slightly annoying”
  • 2: “Annoying”
  • 1: “Very annoying”

Bluetooth Codec Comparison

See Chapter 4: Test Method in the test methods document ITU-R BS.1116-3 for more details regarding how the tests have been performed.

Diving deeper

If you are interested to learn more about the new features in Bluetooth 5.2 (including Isochronous Channels), see Bluetooth 5.2 Feature Overview. To get even more into the details, the complete Core Specification is there for you.

 

// Johannes Jansson, Software Developer