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In this guide by Witekio our engineers examine the possibilities of BLE Audio for device makers. Introduced in Bluetooth 5.2, Bluetooth Low Energy opens the door to new use-cases like broadcast audio, multi-stream synchronization, and ultra-low-power audio streaming.
But with more than 1, 200 pages of new specifications, evolving interoperability standards, and a rapidly shifting device landscape, it’s hard to know where to begin. This guide is here to help you cut through the noise.
Whether you're building next-gen earbuds, hearing aids, public broadcast systems, or consumer electronics, this guide explains:
- What BLE Audio actually is, and how it differs from Bluetooth Classic
- What new features and opportunities it enables
- The architecture and building blocks of a BLE Audio system
- Why BLE Audio is worth considering now—even if market adoption is still growing
- What to look out for when developing your own BLE Audio-enabled product
Bluetooth Low Energy Audio is a feature first introduced in version 5.2 of the Bluetooth specification, allowing for audio streaming over a Bluetooth LE transport.
It promises increased flexibility, lower power consumption and support for a whole host of new use-cases. Most devices on the market using Bluetooth audio today use “Bluetooth Classic”, also known as BR/EDR Bluetooth.
While Bluetooth Low Energy (BLE) uses the same 2.4 GHz frequency band as Bluetooth Classic, it is a fundamentally different technology all the way down to the physical layer. BLE is designed to minimise power consumption by only turning the radio on when absolutely necessary.
Typical use-cases for BLE are low data-rate communications with constrained devices where maximising battery life is important – for example, a heart-rate monitor or other wearable device.
Up until recently, BLE has not supported audio streaming. The low-level “isochronous channels” underlying BLE Audio support were first defined in version 5.2 of the Bluetooth spec in 2020, closely followed by specs for the higher-level features and profiles needed to fully support an LE Audio device.
What’s Wrong With Bluetooth Classic Audio?Flexibility
Audio support in Bluetooth Classic evolved in the early 2000’s to support two main use-cases:
Hands-free Profile (HFP): developed to allow phone-calls to be taken hands-free in a car. Optimised for low-latency, low-quality, bidirectional mono audio stream for voice transmission.
Advanced Audio Distribution Profile (A2DP): developed for listening to music. Aimed at high-quality music streaming from a single source device to a single receiver, with no return path.
As technology has moved on, new use-cases don’t fit either option well. The most popular example is wireless earbuds, where left and right earbuds are completely separate with no wired connection between them.
This poses a problem for the A2DP profile – it is designed around a single point-to-point connection, not a connection between a phone and two separate earbud devices.
Clearly, there are plenty of these devices on the market already without BLE audio. So how does this work?
In fact, “True Wireless Stereo” requires proprietary extensions on top of the profiles defined in the Bluetooth specification.
The two most common solutions are illustrated below:
Replay scheme: One earbud maintains a connection with the phone, transferring stereo audio via the A2DP profile. One of the channels is then passed on to the second earbud via another method, while the first earbud delays playing the audio until it knows that the second has had time to receive and decode it.
Sniffing approach: One earbud communicates directly with the phone, setting up the audio stream and acknowledging data that is received. It also shares information with the second earbud which allows it to synchronise with and decode the same audio stream.
Both methods require proprietary extensions at a low level within the Bluetooth stack, and might even need a second radio operating on a different frequency band to communicate between the two earbuds (Bluetooth signals donʼt travel through your head very well)!
Power ConsumptionAnother key drawback of Bluetooth Classic audio is power usage.
BLE was designed from the ground up with minimal power consumption in mind (hence why “Low Energy” is even in the name).
Bluetooth Classic on the other hand uses a higher data rate and generally needs to keep the radio turned on for longer periods of time.
Increased battery life is a nice-to-have for consumer products. However, one of the main drivers behind BLE Audio is the hearing aid industry, where a typical device might need to be turned on and actively in use for the entire day while still fitting into a tiny package size.
This makes minimising power consumption critical to an effective product.
There are too many new and interesting features to cover them all here, but weʼll go over a few of the highlights.
Streaming transport - Isochronous channels
Firstly, a quick overview of the low level “isochronous channels” feature that underpins Bluetooth LE Audio. This introduces a new low-level physical channel type intended purely for streaming data without any associated control information. Any required control information (for example play/pause, volume control etc.) continues to use the existing GATT procedures that are used for non-audio BLE applications.
An isochronous channel transmits packets at a fixed time interval, for example every 10 milliseconds. Multiple packets may be sent at each ISO event, and packets may be re-transmitted during the same ISO event or a subsequent one if the receiver did not acknowledge the packet, helping to achieve reliable data transmission and minimise data loss even in a noisy environment.
When no more packets need to be sent at a given ISO event, both the sender and receiver can turn off their radios – this is key to the power savings offered by BLE audio.
In contrast to the typical GATT communications used by BLE devices, isochronous channels allow the application to access precise timing information, which is needed to synchronise audio recording and/or playback between multiple wireless devices.
Precise timing is surprisingly important in BLE audio – the human brain is very good at detecting differences in the timing of sound arriving at each ear, as this is used to determine which direction the sound is coming from.
For an audio source 2 metres away, a timing difference of only 70 microseconds between the left and right ears has the same effect as a head rotation of 10 degrees.
Typically, audio across two earbuds must be rendered within 25 microseconds of each other for this effect to be imperceptible to the user.
In contrast to Bluetooth Classic, BLE audio builds time synchronisation between different devices into the spec itself.
The concept of a common “synchronisation point” is introduced – this is the point in time at which all receivers have had every chance to receive any given audio packet (including re-transmissions).
Each stream also has an associated “presentation delay” - this is a fixed amount of time the audio stream should be delayed by to ensure that each device has sufficient time to decode the stream and perform any processing, for example active noise cancellation or other audio manipulation.
If a device knows the synchronisation point associated with each packet and the presentation delay of the stream, it can ensure that the audio data is played back at precisely the right moment in time to be synchronised with any other devices using the same stream.
Broadcast AudioHearing aids have used the “telecoil” system for broadcast audio within public spaces for many years.
However this has a number of limitations:
- Telecoil audio loops cannot overlap, so only one audio stream can be broadcast in a given area.
- The induction loop used to transmit the audio stream is physically large (typically enclosing the entire space within which the audio is available) and therefore difficult to install.
- This technology is generally not used by consumer devices such as phones, TVʼs and earbuds.
Broadcast audio over BLE is intended as a replacement for this telecoil system, which also opens up possibilities for a number of new use cases.
Multiple broadcast streams can be transmitted at once in the same location. Imagine for example an airport, where announcements can be broadcast in multiple languages, and people can choose which one to listen to on either a hearing aid or even a pair of normal headphones.
Transmitting a broadcast audio stream just requires a chip supporting BLE audio, rather than a bulky and power hungry telecoil system. As well as making systems in public spaces cheaper and easier to install, it opens up possibilities such as broadcasting music from your phone or audio from a TV to multiple sets of headphones simultaneously.
Broadcast streams can also be encrypted for privacy. This allows for sharing a broadcast between a select group of receivers without it being publicly available.
LC3 codecExisting Bluetooth Classic profiles are focused on either low-quality but low-latency voice data, or high-quality but higher latency audio data.
BLE audio aims to cover a wider range of use cases, with more flexibility in the exact trade offs between quality, data rate and latency. To support this, a new audio codec known as “LC3” is introduced.
All BLE audio products should support the LC3 codec (similarly to how SBC codec support is mandatory for Bluetooth Classic audio) to guarantee some level of compatibility between products from different manufacturers. But there is also the possibility to choose a different codec if all devices involved in a connection agree on this.
The LC3 codec aims to provide equivalent or better audio quality to the SBC codec at much lower bitrates. This is another way in which power consumption can be reduced – if less data needs to be transmitted for the same audio quality, then the radio can remain turned off for longer.
While audio quality is highly subjective, the graph below shows promising results when compared to the SBC codec.
The final piece that ties together Bluetooth LE audio into a coherent system is the high-level profiles and services.
Bluetooth Classic has two profiles for audio as discussed earlier – HFP for hands-free phone calls, and A2DP for music. BLE audio aims for a more modular and flexible approach by splitting functionality into a much larger number of profiles, which each cover small areas of functionality.
For example, the Basic Audio Profile (BAP), handles managing unicast and broadcast audio streams, the Volume Control Service (VCS) handles overall volume control, and there are many other profiles and services available to cover functionality such as publishing the capability of any given device, agreeing which audio stream settings to use for a stream, or controlling playback of audio (play/pause/skip tracks etc).
Some key profiles to take a look at are:
- TMAP: Telephony and Media Audio Profile. This essentially covers the use cases of the Bluetooth Classic HFP and A2DP profiles, so should the the first place to look if migrating a device from Bluetooth Classic to LE without adding any new functionality.
- HAP: Hearing Access Profile. This is the top-level specification for hearing aid devices.
- PBP: Public Broadcast Profile. This covers configuring a broadcast audio stream in a way that allows any acceptor to receive and decode it.
While Bluetooth LE audio opens up the possibility for improved power consumption along with new features and use-cases, this comes with additional complexity. Around 1250 pages of Bluetooth spec documents have been added to cover LE audio, which is a challenge to fully digest and understand!
With any new specification of this level of complexity, itʼs likely that a few issues and ambiguities will be encountered by early adopters. Designing a new product based around LE audio will be difficult while there are few other devices in the market to test it against, in particular ones supporting entirely new use-cases such as broadcast audio.
Some early products have mitigated against interoperability issues by providing a full “end-to-end" solution, for example a set of headphones and a USB broadcast transmitter sold together, without any obvious way to use it along with another manufacturerʼs products.
But as the spec and products implementing it become more mature, the situation should improve to the point weʼre at with Bluetooth Classic today, where you can buy any set of Bluetooth headphones and expect it to “just work” along with your phone, PC, tablet or any other device.
AdoptionWhile the spec for BLE Audio has been around for a few years and adoption is gradually increasing, progress is still slow. Part of this could be down to the fact that both sides of the connection need to support the new protocol for it to work.
Until smartphones support the new protocol, there is little demand for headphones or other devices using BLE audio.
But adding support to a smartphone is not much of a selling point until there are widely available BLE Audio headphones and earbuds.
Most BLE Audio devices available on the market now also support Bluetooth Classic as a fallback option, with the increased battery life and new features like broadcast audio only becoming available if both sides of the connection support it.
In the short term, we expect this to be the way most devices go. But long-term as adoption increases, there is an opportunity to save on cost and complexity by dropping support for Bluetooth Classic audio completely – although it remains to be seen how long this will take.
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