Bluetooth LE Audio: A Comprehensive Overview
Wireless audio transmission is one of the primary applications of Bluetooth®. Today, billions of headphones, speakers, mics, and earbuds use Bluetooth® BR/EDR connection.
Almost every Bluetooth® device now uses Bluetooth® Low Energy, except for audio streaming devices that require a Dual Mode controller for streaming audio over Classic Bluetooth®. To address this, the Bluetooth® Special Interest Group (Bluetooth® SIG) developed a solution to enable and enhance streaming audio over Bluetooth® Low Energy, paving the way for the next generation of Bluetooth® audio.
Bluetooth® Low Energy (LE) Audio was initially designed for low-power communication, ideal for connecting wearables or peripherals with small data packets. With Bluetooth® 5.2, the Bluetooth® SIG paved the way for the future of Bluetooth® LE Audio by introducing different types of isochronous streams: connected isochronous streams (CIS) and broadcast isochronous streams (BIS).
LE Audio operates on the Bluetooth LE standard and is designed to support the development of the same audio products and use cases as classic audio, while also improving the performance of classic audio products.
Key Features of Bluetooth LE Audio
Bluetooth® Low Energy Audio is based on a new audio codec: LC3 for Low Complexity Communication Codec. The groundbreaking features of Bluetooth® LE Audio usher in a new era, expanding support beyond basic speech communication and audio streaming.
Here's an illustration of the salient features of LE audio:
Low Complexity Communication Codec (LC3)
LE audio includes a new high quality, low power codec, known as LC3. LC3 delivers high quality audio at low data rates. This offers a high level of flexibility and strikes a good balance between high audio quality and low data rate.
Compared to the SBC codec used in classic audio, LC3 is much more efficient in processing and delivering audio, resulting in a better audio experience to end users. The LC3 codec is designed to have an efficient tradeoff between sound quality and power consumption.
The Bluetooth SIG claims that the SBC codec encodes a 1.5 Mbps audio stream to a 345 Kbps stream, while Bluetooth LE Audio will compress it at 160 Kbps - which will take up much less bandwidth. Despite this lower bitrate (48 kHz, 32-bit audio at bitrates from 16 to 425 Kbps), the Bluetooth SIG quotes from a listening test that Bluetooth LE Audio's sound quality is perceived as better than that achieved by Bluetooth Classic.
LC3 also reduces the need for vendor-specific codecs and proprietary solutions, resulting in lower device costs. It supports standards-based implementations, offering a high level of flexibility and striking a good balance between high audio quality and low data rate.
Isochronous Channels: CIS and BIS
With Bluetooth® 5.2, different types of isochronous streams were introduced: connected isochronous streams (CIS) and broadcast isochronous streams (BIS).
- Connected Isochronous Stream (CIS): Ideal for audio streaming between a single source and a single sink.
- Broadcast Isochronous Stream (BIS): Enables the broadcast of audio streams from a single source to multiple sinks.
LE audio includes a new logical transport comprised of a connected isochronous stream (CIS) and connected isochronous group (CIG). A CIG comprises one or more CISes that need to have a time relationship at the application layer, or of a single CIS. The maximum number of CISs in a CIG is 31.
The CIS and CIG servicing left and right stereo ear buds
CIS is ideal for audio streaming between a single source and a single sink, while BIS enables the broadcast of audio streams from a single source to multiple sinks. This evolution also brought forth a new, low-complexity communications codec (LC3), which offers a high level of flexibility and strikes a good balance between high audio quality and low data rate.
Multi-Stream Audio
LE audio now supports multiple isochronous audio streams with synchronization between them. This allows for multiple isochronous audio streams with synchronization between them, making switching between multiple audio source devices smoother.
Hearing Aids Support
LE audio provides exclusive support for hearing aids, which require low and efficient power consumption. Microsoft recently brought Bluetooth LE Audio to a Windows 11 Preview Build beta, letting wearers pair their hearing aid direct to their PC to take calls, listen to music and stream audio.
Auracast Broadcast Audio
LE Audio introduces audio broadcasting, also known as AURACAST®, opening up possibilities for public audio scenarios. Auracast enables an audio source device to broadcast to an unlimited number of audio sink devices through Auracast broadcast. Auracast is introduced as a new Bluetooth use case, audio sharing. Imagine tuning into a silent TV at a restaurant, receiving public announcements at a train station through your earbuds, or immersing yourself in a live music performance for an exceptional listening experience even in noisy environments.
Changes to Link Layer (LL) State Machine
The Bluetooth data transport architecture now supports LE isochronous channels. These isochronous channels can be connection-oriented or connectionless.
Isochronous communication is realized using the new LE isochronous physical channel. This physical channel uses frequency hopping and specifies the timing of the first packet. The timing acts as a reference point for the timing of the subsequent packets. The LL transmits the isochronous data packets on an isochronous physical channel.
LE audio has the following logical links:
- LE-S: Used to transmit audio data
- LE-F: Used to transmit framed data packets
- LEB-C: Used for control requirements
A flushing period is specified for the LE-CIS logical transport. Any packet that has not been transmitted within the flushing period is discarded. The LEB-C logical link is used for control requirements, and supports only unidirectional communication.
Bluetooth LE Audio Testing
High audio and speech quality are paramount for delivering an exceptional mobile user experience. Bluetooth® wireless testing, coupled with comprehensive audio performance measurements, is key to accelerating the development of Bluetooth® audio devices.
Rohde & Schwarz test and measurement solutions are designed to comply with the latest Bluetooth® core specifications. Bluetooth® test functions are embedded across all major Rohde & Schwarz test instruments, including signal generators and analyzers. These solutions cover Bluetooth® BR, EDR, and LE and are suitable for the entire development cycle - design, certification, and production.
The R&S®CMW500/270 serves as an ideal foundation for Bluetooth® audio testing, offering support for the most crucial audio profiles, mandatory codecs (CSVD, SBC, LC3), and a range of options for conducting audio performance measurements. These measurements include single and multi-tone assessments of output power, signal-to-noise ratio (SNR), total harmonic distortion (THD) and signal-to-noise and distortion (SINAD), among others, providing a holistic evaluation of audio device performance.
It has the unique capability to seamlessly integrate Bluetooth® RF testing with audio testing, and it features in-radio test control for DTM-like testing of Bluetooth® LE devices in an over the air (OTA) setup. This setup enables the simultaneous verification of audio performance and wireless Bluetooth® connection. It also provides the flexibility to experiment with various communication parameters.
There is also the option to integrate applicable audio quality measurement equipment for more advanced audio quality measurements, such as perceptual objective listening quality analysis (POLQA) or perceptual audio quality measurement (PEAQ). Additionally, the system supports an echo mode with a Bluetooth® loopback - ideal for functional testing in manufacturing.
Devices Supporting Bluetooth LE Audio
In order to support Bluetooth LE Audio, a device must have Bluetooth 5.2 or 5.3. But beware - not all devices that support those versions of Bluetooth support LE Audio. Some will stick with Bluetooth Classic Audio.
Both the source (i.e. phone, tablet, computer etc) and sink (i.e. wireless headphones, wireless speaker) device must support Bluetooth LE Audio in order for it to work. But with most LE Audio devices also supporting Bluetooth Classic Audio, your sink and source device should still work together, just maybe without all the benefits of LE Audio.
Devices compatible with Bluetooth LE Audio include the Google Pixel 7/8, Samsung Galaxy S23, Samsung Galaxy Z Fold 4 and Galaxy Z Flip 4 smartphones. When it comes to headphones the Samsung Galaxy Buds 2 Pro, OnePlus Buds Pro 2 and Earfun Air Pro 3 true wireless earbuds are also confirmed to support it.
Development Tools for LE Audio Products
LE Audio is the next generation of Bluetooth Audio, making audio streaming over Bluetooth Low Energy possible. Bluetooth LE Audio is developed to enhance performance in power consumption, latency, and bandwidth. LE Audio and Classic Audio standards will continue to coexist and have features that will be supported by both.
Development tools that make it easy to develop LE Audio products include:
- nRF Connect for Desktop is a cross-platform framework for development applications.