Bluetooth LE Audio: audio quality, music sharing, LC3 codec…everything you need to know about the new Bluetooth standard

Bluetooth LE Audio will revolutionize the way we listen to music. A great new feature of the Bluetooth LE Audio standard, Auracast Music Sharing allows the same audio stream to be broadcast to multiple speakers, headphones or earbuds. Bluetooth LE Audio also introduces a new reference codec, the LC3, which consumes little power and is compatible with 5.1 multi-channel audio. Features, benefits, uses, we explain everything about Bluetooth LE Audio.

The Google Pixel Buds Pro to illustrate // Source: Chloé Pertuis for Frandroid

More than two decades after its creation, the Bluetooth standard is on the way to undergoing a major evolution and freeing itself from numerous constraints. The ban on connecting to a single audio device for music playback is on the verge of a breakthrough, as is the inability to make calls while listening to music. And thanks to the Bluetooth LE audio standard.

What is Bluetooth LE audio?

It’s a complete rewrite of the way sound is delivered that the Bluetooth LE Audio standard offers. Introduced in 2010 with Bluetooth 4.0 controllers, Bluetooth Low Energy (LE) technology has never been used to transmit sound, only to transmit small amounts of data, for example from a connected bracelet to a smartphone, or to control certain functions of wireless headphones and earphones. Sound transmission has always been the prerogative of the classic Bluetooth radio connection (Bluetooth Classic Audio), via the profiles A2DP (Advanced Audio Distribution Profile) for music and HFP for telephone calls.

Go beyond the limits of classic Bluetooth in audio

Although it has evolved over the years and revisions, the Bluetooth Classic Audio standard maintains an architecture that was conceived over 20 years ago when the primary need was to pair a wireless headset with a smartphone for hands-free audio calls to do. Therefore, Bluetooth Classic’s HFP (Hand Free Profile) profile still uses low-quality audio compression technology, which is unsuitable for streaming music in Hi-Fi conditions.

Bluetooth LE audio
Source: Bluetooth SIG

The A2DP profile, later developed for listening to music – and using the famous codecs SBC, AAC, aptX or even LDAC – suffers from a major flaw: it is unidirectional. It is therefore not possible to use the microphone of a Bluetooth headset to make calls or to use the voice assistant of a smartphone while listening to music. It is also not possible to stream music via Bluetooth Classic to multiple headphones, earphones or speakers. With the Bluetooth LE Audio standard, that all changes and it will finally be possible to play with Bluetooth headphones or earphones.

What are the new features of Bluetooth LE Audio?

Auracast technology is the great novelty of the Bluetooth LE Audio standard. Auracast allows music to be streamed to multiple devices (speakers, headphones, earphones, hearing aids, etc.) simultaneously. To do this, simply activate the sharing of the current measured value, possibly associated with a password to secure access. Auracast opens up new possibilities for listening to audio content in public places, especially museums, where listeners can use their own headphones or earphones without lengthy pairing. The integration of Auracast technology into TVs is also said to make it easier to distribute sound to multiple users, especially those equipped with compatible hearing aids. For the latter, the ability to easily connect to many audio sources could bring a lot of convenience.

Bluetooth LE audio
Source: Bluetooth SIG

Simultaneous streaming to multiple Bluetooth audio receivers, called Multistream Audio, could also affect the operation of the true wireless headphones. With classic Bluetooth, the stereo audio signal is sent to one of the headphones, which transmits to the other the channel it needs to transmit. This has the effect of inducing additional latency in sound propagation as it consumes energy. More flexible in operation, Bluetooth LE Audio allows a smartphone to send each earbud the channel it needs to send, reducing latency and inevitably reducing earbud power consumption.

Bluetooth audio becomes multi-channel

The Bluetooth LE Audio standard also brings compatibility with 5.1 multi-channel sound. Up to now, classic Bluetooth only allowed audio transmission in mono or stereo. A home cinema receiver or soundbar compatible with Bluetooth LE Audio can now receive a multi-channel title and transmit 5.1 surround sound. This new feature opens up the possibility of assembling multiple LE Audio Bluetooth speakers into a small home theater system by telling the Bluetooth source which speaker is left, centre, right, behind you and even which should act as a subwoofer. If Netflix and co. play the game, as does Apple Music with its catalog of titles in Dolby Atmos 5.1, it could significantly change the way we listen to music, films and TV series.

The LC3 codec at the heart of Bluetooth LE Audio

The Bluetooth LE Audio standard introduces a new Bluetooth audio codec called LC3 (Low Complexity Communication Codec) that must be integrated into BT LE Audio certified smartphones and audio devices. According to the Bluetooth SIG (Special Interest Group), the LC3 codec offers excellent sound quality, which is better than the Bluetooth Classic SBC (sub-band) codec at the same bit rate. Developed by Fraunhofer IIS Institute (the inventor of MP3) and Ericsson, the LC3 codec would make it possible to obtain premium sound with a data rate ranging from 160 kbps to 250 kbps, depending on the encoding profile, for streams with audio sampling at 48 kHz (movies , series, videos) and about 200 kbps for audio streams sampled at 44.1 kHz (music). These rather low bit rates make it possible to limit the energy consumption during radio transmission.

According to the Bluetooth SIG, the LC3 codec would provide the SBC with superior quality
According to the Bluetooth SIG, the LC3 codec would give the SBC better quality // Source: Bluetooth SIG

Let’s be clear, there will be no qualitative revolution, most competing codecs (aptX, AAC, etc.) offer similar bitrates and already very good sound quality. In addition, the LC3 codec also uses degrading compression, which removes certain tones that are considered inaudible, attenuates high frequencies, and reduces overall dynamic range.

Compatible with Bluetooth LE Audio, aptX HD or LDAC

While the Bluetooth SIG has made the LC3 codec mandatory for Bluetooth LE audio, the organization does not preclude the use of other codecs by manufacturers. So we can imagine that Apple’s AAC codecs, Qualcomm’s aptX or Sony’s LDAC will eventually be implemented in smartphones, headsets and Bluetooth LE audio speakers. With a usable bandwidth of around 1 MBit/s – as with classic Bluetooth – Bluetooth LE Audio could, for example, enable stereo transmission in CD quality with the aptX Lossless Codec.

However, remember that the quality of sound transmission through headphones, earphones and speakers mainly depends on the quality of the speakers used and the associated amplifier. Headphones with inferior drivers, even when driven by a lossless audio signal, still sound (much) worse than high-performance headphones that play heavily compressed audio.

Better audio quality for calls

Bluetooth LE Audio offers better support for calls in VoLTE (Voice over LTE), i.e. in HiFi quality in 4G and 5G networks.Until now, the HFP profile of classic Bluetooth and its prehistoric codec degraded the quality of calls with headphones or clearly headphones. Bluetooth LE audio now uses the LC3 codec. This allows the listener to enjoy much better sound during phone calls in general and VoLTE calls in particular. Likewise, the interlocutor hears better because the sound from the microphone integrated in the helmet is now compressed in LC3.

Lower latency… or not

The Bluetooth SIG claims that the LC3 codec significantly reduces audio streaming latency. In other words, the delay between image and sound transmitted via Bluetooth would be reduced thanks to the new codec. The encoding, radio transmission and decoding time would be as little as 20 milliseconds, according to the organization, a figure low enough to be imperceptible. However, this performance correlates with a low data rate and poor QoS (Quality of Service), i.e. heavily compressed audio and minimal connection stability. It can be assumed that most audio device manufacturers will opt for high QoS, i.e. a stable Bluetooth connection with buffering of the received data to avoid artifacts and playback interruptions, especially in wireless environments. – Disturbed frequencies (public places, public transport, etc.).

Bluetooth LE audio

This could double or triple the announced 20 ms. In addition, the audio post-processing (equalization, ANC, etc.) carried out after receiving the audio data increases the latency a little. In short, Bluetooth audio latency seems like a fatality that we need to solve, especially since it only really affects video games. Reading films or series is already subject to an upstream audio-video synchronization correction.

Bluetooth LE Audio: power consumption and range

Since the introduction of Bluetooth LE, the low power consumption argument has been systematically advanced. However, this energy sobriety needs to be brought closer to the concrete applications of Bluetooth LE. In fact, activating the Bluetooth controller occasionally and transferring a few bytes from a connected bracelet requires infinitely less energy than continuously sending streams of audio data, which can be tens or hundreds of megabytes in long streaming listening sessions. So it is by no means certain that Bluetooth LE Audio consumes less energy than Bluetooth Audio Classic at a comparable data rate.

The radio coverage of Bluetooth LE is identical to that of classic Bluetooth. Depending on the device class, the range can vary between 10 and a maximum of 100 meters. Of course, these numbers should be taken with caution, since the presence of obstacles (partitions, floors, objects, etc.) and radio frequency interference (computers, smartphones, WiFi routers, etc.) can reduce coverage.

Which Bluetooth LE Audio compatible smartphones, headphones and earphones are there?

If it seems certain that new smartphones, computers, headphones and headsets with Bluetooth LE Audio support will be marketed in the future, then a little patience is certainly required. Currently, no operating system, Android and iOS at the forefront, support Bluetooth LE Audio.

For Android, this could come with version 13 of the operating system, while Apple hasn’t announced anything for iOS or Mac OS at this time. Helmets, headphones or speakers are nothing, for example, in the Qualcomm catalog, despite the availability of certified chips. B. with headphones and earphones that already have a Bluetooth LE chip, to manage advanced settings from the smartphone (ANC power, equalization, key programming, etc.). firmware Supporting the LC3 codec and Auracast seems technically feasible. The user would also have everything to gain.

Whether manufacturers will have to play along or equip themselves with new smartphones, helmets, earbuds or speakers to take advantage of Bluetooth LE Audio and Auracast Broadcast Sharing remains to be seen. Be continued…

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