BLE Audio and its place in the evolution of Bluetooth
On 9th December 2020, the Bluetooth SIG released revision 5.2 of Bluetooth. One of the key upgrades was the addition of BLE Audio (“Bluetooth Low Energy Audio”). Releasing a spec is just the start of a process. It is only today that real IOT devices are finally available with BLE Audio capability.
Read the article on Electronics Weekly
Introduction to BLE Audio
So, what is BLE Audio and what specification enhancements were required? In many ways it isn’t complicated.
Up to version BLE 5.1, the focus was data transmission for IOT wireless data exchanges. Under this type of use-case the focus was “Reliable Data Transmission”. This means that if a data packet is lost (which is normal for wireless), the system retries the transmission. So all the data arrives, albeit with some delay. This is what IOT customers want. Furthermore the “Low Energy” aspect of BLE the model is ideal for IOT devices which require occasional data transmission and spend the rest of their time in sleep mode. Also the initial generation of BLE devices lacked the processing power and memory for sophisticated applications.
Could BLE audio have been implemented earlier? Technically (kind of) yes – with great effort. However, it simply wasn’t a priority because the original BT Classic (“Bluetooth Classic”) did the job. BLE specs focused on applications which BT Classic couldn’t support.
BT Classic and BLE
Bluetooth-now referred to as “Bluetooth Classic” was launched in 1999. The idea was a “cable replacement technology” that could link diverse devices. It was for “local” connections i.e., around 10-20m and for simple low data rate applications, initially at rates of 1Mbit/s base rate, with real throughput at best half that, less if over longer distance or with obstacles.
However, some technical issues limited take-up. These were:
- It required constant wireless data connection meaning devices quickly drained power. Users found in many cases the problems outweighed the benefits.
- Although Bluetooth is open and interoperable, in practice, interoperability was poor.
- Connecting two devices with any kind of security was hard.
- Recovery from connection loss often failed. So, you needed to start again.
So overall, initially Bluetooth Classic had little traction and was misunderstood. Users found the technology more troublesome than helpful, especially the aspect of keeping devices powered. Cables seemed easier.
Evolution of Bluetooth
However, as is often the way with technology, the “early adopters” persisted. Technology gradually progressed, and some specific use cases started to become popular. The silicon chips and modules used for Bluetooth significantly improved.
These cases were the wireless mouse and keyboard, and streaming audio – the latter being the one which users seemed willing to keep charging devices for.
For audio streaming, the initial devices were a simple “single ear bud connected to a phone”. The quality was poor. Over time – more than a decade – quality improved. We reached the point where today’s HiFi quality solutions are extremely popular. These solutions will persist for many years due to the sheer quantity of legacy devices that will remain in use by consumers. The popularity of Bluetooth is guaranteed, due to its native presence on computers, tablets, and smartphones.
Bluetooth and BLE merge
Bluetooth Low Energy, launched in 2009, was aimed at a different kind of use case. It sought to fulfil the original vision of cable replacement.
Why BLE Audio today?
There are a few reasons. The main ones are that it makes no sense to maintain two parallel Bluetooth standards and that the Bluetooth chips and modules have improved so much that they can cover both protocols.
So, what is Bluetooth Low Energy Audio and is it the same as Bluetooth Classic? The simple answer is no, it is better. This means specifically it consumes less power, has longer range and offers a higher quality audio solution. Note that both Bluetooth Low Energy and Bluetooth Classic use the same 2Mbit/s raw data rate and identical over-the-air encoding schemes.
What technically is BLE?
For an Audio Solution, you do not want “unreliable data transmission” as described above because this would give you a “gappy” sound. If packets need to be held for a retry for Audio, you want a “streaming approach”. You try to send a packet. If it doesn’t arrive, you note it, but just move to the next regardless. Listeners hardly notice. Only in a major packet loss will you hear a noticeable drop in sound quality, and even so streaming is still the best approach. This feature is called “Isochronous Channels”.
Strictly speaking LC3 CODEC is not part of BLE 5.2, in the sense that the CODEC could be used for any compression/decompression task. But it is interesting because it gives good “perceived audio quality” at a lower data rate than the current CODECS. Note BLE 5.2 did NOT provide any data increase. It remains at a (nominal) 2 Mbits/s with a max theoretical “ideal” real throughput at c. 1 Mbs. In the real world, at a realistic distance and use case, it will drop off further with range.
The benefits of Bluetooth Low Energy are:
- Lower power consumption
- Better audio quality
- In certain use cases, simpler technical implementation
- Better latency
How technically BLE achieves these benefits
Lower power consumption is achieved by Bluetooth Low Energy allowing the radio to “drop to sleep” if there is no data to transmit. One could expect that for an audio stream, the radio might be on a large fraction of the time. Nevertheless, there will times when this is not the case – quiet passages, gaps between tracks, simple passages of music, voice calls and so on. One could imagine the power savings to be down to 50% or less, depending on exact circumstances. The “data intensity” of an audio stream is quite variable, depending on its nature.
Better Audio Quality
This is achieved via the LC3 CODEC, as noted above, not strictly speaking part of the Bluetooth audio specification.
Earbuds use case
Bluetooth Classic has a single over-the-air wireless data stream. For a connection to over ear headphones this is fine as a wire can be run inside the headband. For earbuds, which are very popular, this is an issue.
It is necessary for the source, typically a smartphone, to stream to one earbud in stereo. Then this earbud must stream the other channel to the second earbud. This means the mid-earbud requires more complicated hardware and software. It can also lead to poor audio quality, as the wireless signal must “traverse the head”, which leads to possible loss in audio quality.
New BLE Audio Features
In addition to these advantages Bluetooth Low Energy offers some new features. These are:
- Multicast, known by the brand “Auracast”. This allows one source (smartphone) to transmit to several “sinks” (speakers, headphones). This solves the “earbud problem,” and creates some new opportunities.
- A single source can transmit a different stream to many sinks.
The maximum number of sinks supported is 31, although it is doubtful that any hardware exists to support this number. But an advanced audio standard like Dolby 7.1 could be supported.
Possible new Use-Cases for BLE Audio
- Public space receipt of audio stream on personal headphones. One could imagine in a public space, say an airport or train station, where there is a screen showing content, or just noise making it hard to hear announcements. An Auracast stream can allow the user to enjoy the content or hear the announcement above the noise.
- Surround sound. A multichannel solution can allow a surround sound experience via BLE audio.
- Live performance. A multichannel solution can allow a wireless solution of multiple instruments playing together.
- Multi-language. In an international conference a multichannel wireless solution could enable participants to select their language of choice, as provided by interpreting services. This kind of service of course already exists, but typically via wired and switched headsets, often requiring a seated environment. A wireless solution, by contrast, would for example allow a speech at a reception, say, to be translated, whilst delegates circulated.
Current state of play of BLE Audio compatible hardware solutions
Today the first generation of audio products supporting Bluetooth Low Energy Audio including headphones are now on the market. Phones, tablets and computers are progressively being equipped and upgraded with the supported hardware and software. Often only a software upgrade is required.
As with any new technology, full rollout and adoption takes time. But a higher quality, lower power Bluetooth Low Energy is coming!
Dr Nick Wood
Sales and Marketing Director