LE Audio technology will leverage the entire wireless audio market

Bluetooth technology has been divided into two branches since version 4.0: Bluetooth Low Energy (BLE), as a rising star, has developed rapidly with the help of the Internet of Things and has become the standard for many innovative IoT applications such as wearables; while Classic Bluetooth (BT) has been sticking to audio and high-speed data transmission, the traditional base of Bluetooth technology, and has been mediocre.

In the past four or five years, classic Bluetooth has ushered in a new wave of growth in the field of audio transmission, mainly thanks to Apple's AirPods. This successful product has brought a new TWS true wireless stereo headset product category. According to Counterpoint's market research data, the global TWS headset market will grow by 33% year-on-year in 2021, reaching 310 million units.

The dilemma of TWS
However, as more and more people enter the field of TWS, everyone has increasingly realized how deep the "pit" left by classic Bluetooth for TWS is - in many aspects, the original classic Bluetooth audio transmission standard can no longer meet the development requirements of TWS. There are two main slots:

First, the coding technology has limitations. Classic Bluetooth uses SBC coding technology, which was OK for transmitting telephone voice in the early stage, but when faced with audio applications with high user experience requirements such as music playback, its weaknesses of low efficiency and poor sound quality are exposed. Therefore, in people's traditional perception, the sound quality of Bluetooth headsets is just "listening to the sound". There are ways to improve the sound quality, which requires the use of other proprietary coding solutions, such as AC3 and AptX coding, but manufacturers and users have to pay extra hardware costs and technology licensing fees for this, which is obviously not the best solution.

Second, it is too difficult to synchronize both ears. Classic Bluetooth can only support a single point-to-point audio stream on the A2DP profile, while TWS needs to transmit the audio to two separate earphones. For this reason, the traditional solution is to first transmit the audio to the earphone on one side (host), and then connect the host to the earphone on the other side (slave). However, this master-slave TWS solution has obvious weaknesses: first, the host acts as a signal relay, which consumes more power and ages faster, which will cause differences in the battery life and service life of the earphones on both sides; second, the audio of the earphones on both sides is not synchronized, and the delay between the picture and sound of the mobile phone is too large - this is undoubtedly a fatal flaw for video and game parties.

In order to solve the problem of asynchronous binaural audio, various TWS manufacturers are also actively looking for solutions. Apple has solved this problem well on AirPods through a proprietary monitoring solution, but the strict patent barriers it has built have deterred other latecomers. In recent years, many binaural connection solutions have also made great progress, but these protocols and implementation solutions are not "one family" after all, and compatibility issues are inevitably a headache - for example, Qualcomm's TWS+ solution only supports mobile phone platforms above Snapdragon 845.

It can be seen that all the efforts to "fill the gaps" mentioned above are just patching up the original Bluetooth standard and are far from perfect. To solve the problem fundamentally and fill the "gap" of classic Bluetooth audio transmission, we still need to work hard on the Bluetooth standard.

SIG is well aware of the demand for LE Audio standard
, so it finally released a big trick in the Bluetooth 5.2 standard version launched in early 2020 - launching LE Audio technology. As the name of this technology shows, it is to provide audio transmission through BLE connection (rather than classic Bluetooth), and comprehensively improve the user's wireless audio experience based on the low power consumption characteristics of BLE.

If we say that the development of Bluetooth technology before, BLE and classic Bluetooth were like two parallel lines due to their different application scenarios, now LE Audio makes the two intersect, and it is very likely to touch the "cheese" of classic Bluetooth audio transmission. Therefore, some industry insiders commented that this will be "one of the biggest development achievements in the history of Bluetooth."

So what is the magic of this highly anticipated LE Audio technology? A closer look reveals that this is mainly due to its three newly added skills.

Figure 1: Three key technologies used in LE Audio (Source: SIG)

First, the Low Complexity Communication Codec (LC3),
a new high-quality, low-power audio encoder, has the characteristics of providing high sound quality at low rate conditions. It also supports a wide range of sampling rates, bit rates and frame rates. Developers can flexibly adjust and optimize products as needed to provide users with the best audio experience.

The following figure compares LC3 and the classic SBC encoder. The vertical axis shows the audio impairment scale after encoding and compression based on the ITU-R BS.1116-3 specification - 5 means no difference from the original audio source, 4 means obvious difference but acceptable, and 3 means very obvious difference. It can be seen that LC3 has obvious advantages. Even if the bit rate is reduced by 50%, it can still provide a good audio experience.

It is no exaggeration to say that LC3 enables Bluetooth audio to have the capital to match the HiFi experience under the premise of low power consumption.

Figure 2: Comparison of LC3 and SBC audio coding schemes (Source: SIG)

Second, Multi-Steam Audio technology
can be said to be tailor-made to solve the problem of TWS audio asynchrony. It can realize multiple and independent audio streaming transmissions between a single source device (Source Device) and a single or multiple audio sink devices (Sink Device) of a smartphone. In other words, Multi-Steam Audio technology can send audio streams to both earphones of TWS at the same time, providing a better stereo experience and making the switching between multiple audio source devices smoother, and this is an open technical standard! No wonder once this technology was announced, predictions of "ending the AirPods monopoly" were heard everywhere.

Third, Broadcast Audio technology.
If the introduction of the first two new technologies is to use LE Audio to solve the practical problems encountered by TWS, then broadcast audio technology is to open up greater imagination space for the future of LE Audio.

Based on broadcast audio technology, a single audio source device can broadcast one or more audio streams to an unlimited number of audio receiving devices. A popular understanding is "audio sharing". Moreover, this sharing can be based on individuals or locations, and the application scenarios are wide and flexible. Some applications that we can directly imagine include:

• Personal music sharing: Let multiple friends enjoy the music on a mobile phone (or audio source device) at the same time.

• Public assisted listening: In theaters or museums, multiple users use Bluetooth headphones to listen to drama dialogues or exhibit explanations.

• Public TV/teaching: Fitness coaches can teach target students through Bluetooth headsets, or square dance music no longer needs to be played at a high volume, but can be transmitted to every "auntie" through headphones.

• Multi-language announcements: Use multiple audio streams to enable simultaneous interpretation in multiple languages ​​at international conferences or multi-language announcements on airplanes.

If we continue to expand on this line of thought, the future of broadcast audio technology will be even more exciting.

Figure 3: Bluetooth audio applications will continue to grow in the future (Source: SIG)

At present, various forces have started to lay out around LE Audio. It is expected that the new version of Android system will support LE Audio function in 2022, and the relevant chip research and development work is also in full swing. It is expected that in the first few years of LE Audio entering the market, dual-mode chips that support both LE Audio and classic Bluetooth audio will be the mainstream. Later, with the increase in LE Audio penetration and the expansion of new application scenarios, single-mode LE Audio chips will also be launched one after another.

In short, in the future, more and more good sounds coming out of Bluetooth headsets or other wireless audio devices will be labeled LE Audio.