How much do you know about Bluetooth LE audio technology?

The Bluetooth Special Interest Group (SIG) community supports innovative features including various mesh networks, 512-byte extended advertising, use of a special coded PHY for long-range transmission of about 1 km, location services (indoor positioning services), isochronous channels, and LE audio (Bluetooth 5.2 specification). Each new version of Bluetooth comes with new features and provides multiple application benefits.

About Bluetooth LE Audio Technology:

Bluetooth audio has become a mainstream solution in the market, and most earbuds and headphones use the existing classic Bluetooth technology. However, LE Audio will change the game with the next generation of Bluetooth audio technology. Compared with classic Bluetooth, LE Audio is transmitted over Bluetooth low energy radio and provides high audio quality and lower power consumption. LE Audio has more attractive new features, such as multiple audio streams, broadcast audio streams, and enhancements to Bluetooth audio use cases.

Features of LE Audio:

LC3 Codec Audio:

Typically, an audio codec is used to compress the audio stream at the sender and decompress it at the receiver to play the audio. LE Audio introduces a new codec, the "Low Complexity Communication Codec" (LC3), which enables high quality and low power consumption. LC3 provides better quality at a lower data rate and can provide flexibility to choose between audio quality and power consumption. At the same quality audio, the bit rate is about 50% lower than the SBC codec.

The current classic Bluetooth audio uses the default SBC codec, which is highly flexible for sampling rates up to 48khz and 16-bit depth, and can transmit data up to 345kbps. But its compression algorithm will lose high data. The LC3 audio codec will support various combinations of sampling rates from 8khz to 48khz, with a bit depth of 16, 24, and 32 bits per audio sample. LC3 is a mandatory codec for LE audio, supporting multiple audio channels, which can provide users with high-quality audio, more powerful audio, longer battery life, or smaller product form factors.

Figure 1: Bluetooth codec comparison

Low Energy Audio: The name of LE Audio (Low Energy) is self-explanatory. Its audio capabilities support the Bluetooth Low Energy radio. Obviously, it opens up various opportunities for designing low-power audio applications. Here, most of the use cases will be wearable devices that use battery power.

There is a trade-off between power consumption and audio data rate, where the LC3 codec helps achieve the same audio quality at a 50% lower bit rate, which means the LE radio does not need to be active longer, thus reducing power consumption. Product designs can achieve the same audio quality in a smaller form factor and with a smaller battery size.

Multi-stream audio: Multi-stream audio provides independent, synchronized multiple audio streams between a source device and one or more audio sink devices. For example, a smartphone as a source device and one or two or more earbuds as sink devices. LE Audio takes full advantage of the isochronous channel feature to provide a variety of applications such as true TWS. This feature allows multiple audio streams between source and sink devices, and the error of synchronization accuracy of these streams is about 10-15 microseconds. This feature can provide smoother switching between different audio source devices and helps to implement the functions of A2DP and HFP profiles of classic Bluetooth.

Figure 2: Multi-stream audio

LE Audio multi-streaming can be achieved through Connected Isochronous Streams (CIS), which enables logical transports between connected devices to transmit data on either side of an ACL (Connected Asynchronous Link). Each CIS can use fixed or variable data sizes and framed or unframed data with single or multiple packets on each CIS event. CIS data traffic can be unidirectional or bidirectional between devices, using protocols to improve the reliability of packet delivery in the CIS.

Figure 3: Classic Bluetooth and LE Audio

Broadcast Audio: An innovative feature that enhances use cases in the Bluetooth audio space. It allows one audio source device to broadcast an audio stream to many audio sink devices.

The Broadcast Audio feature can be enabled using "Broadcast Isochronous Stream" (BIS). It is used to broadcast one or more isochronous data streams to all receiving devices within range. It supports fixed or variable sizes, using framed or unframed data or multiple packets on each BIS event. It uses a unidirectional data stream from the source device to the receiving device without acknowledgment. BIS packets can be retransmitted by increasing the number of sub-events in each BIS event to improve the reliability of delivery.

Figure 4: Broadcast audio

Broadcast audio allows receiving devices within range to join the broadcasting audio stream using two broadcast methods:

Open Broadcast: Any receiving device within range can begin receiving the broadcast audio.

Closed Broadcast: Any receiving device in range needs to enter a key to participate in the audio stream from any source device.

Audio sharing can be mainly divided into the following categories:

Personal Audio Sharing: Users can share personal mobile music with friends and family.

Location-based audio sharing: A specific location can enable an audio source device to broadcast its surrounding audio stream to audio sink devices.

For example, airport authorities can set up an audio source device with a common announcement broadcast audio stream, and audio receiving devices (passenger earbuds) within range can simultaneously receive the same audio stream.

Figure 5: Personal and location-based audio sharing

Bluetooth LE Audio use cases:

LE Audio will change the experience in the Bluetooth audio space in different capabilities, enhancing a variety of Bluetooth audio applications. Let’s discuss some industry-specific applications:

Medical industry:

Hearing aids: Bluetooth audio brings more and more consumers to their audio products. The requirements for single or dual hearing aid devices with phone, low power consumption and low latency are increasing rapidly. Hearing aids with LE Audio can provide multi-stream audio traffic to and from the phone and provide individual controls for each audio stream. Overall, LE Audio provides users with "wireless talk, wireless music, wireless viewing and wireless calls".

Figure 6: LE Audio hearing aid

Consumer electronics products:

Audio source device (telephony/media audio): An LE audio source device can send an audio data stream to one or more sink devices as it supports multi-stream capabilities.

Mobile phones, tablets, laptops, TVs, projectors, set-top boxes, streaming media players, etc. are several application scenarios of LE audio source devices.

Audio Sink Device (Phone/Media Audio): The audio sink will receive audio data from one or different source devices. Here, the multi-link feature allows different stream control based on user needs.

Earbuds, headphones, and speakers are some examples of LE Audio Sink devices.

Figure 7: LE Audio Source and Sink Devices

Automotive and Industrial Industries:

Audio source/sink devices (phone/media audio): The automotive industry is rapidly moving toward electric vehicles (EVs). Current infotainment systems use Classic Bluetooth for music and phone profiles, while LE Audio in infotainment will provide additional features, such as audio sharing for music streaming and phone calls, with optimized power consumption.

Figure 8: LE Audio in an infotainment system

Location-based audio: Broadcast audio is a really great feature in LE Audio that can enable many different applications to reach a larger audience. Let’s look at location-based audio with some examples:

Public TV: Public TV in libraries, waiting rooms, gyms, airports, train stations, restaurants, houses of worship, etc. requires public announcement or instruction audio transmission, where LE Broadcast Audio with multiple streams can help achieve this requirement.

Multi-language support: Seminars/conferences need to provide different language translations for participants in different regions, where LE Audio Broadcast multi-streaming will provide various language translations for different participants.

Movie theaters require multi-language support for various native language audio broadcasts, and users can sync their earbuds/headphones and hearing aids to select the language audio stream.