The LE Audio Launchpad
Next Generation Wireless Audio Streaming
Bluetooth® LE Audio is the next generation of wireless audio streaming, with many innovative features to enable a whole new range of market and product creation opportunities for forward-thinking companies.
From hearing aids and wearables for augmented and virtual reality offering greater intelligibility and longer battery life, public information systems offering simultaneous announcements in multiple languages, to the reimagination of live entertainment, LE Audio fundamentally redefines wireless audio streaming experiences.
Classic Audio vs Bluetooth Low Energy
We are all familiar with the one-to-one pairing offered by Bluetooth Classic Audio, wirelessly streaming from our mobile devices to our earbuds, headphones, and personal speakers. In contrast, Bluetooth Low Energy is targeted at applications where power consumption is a key consideration and limited amounts of data are sent on an occasional basis, such as with energy-efficient sensor devices
Whilst sharing the same branding, and indeed Core Specification documentation, Bluetooth Classic Audio and Bluetooth Low Energy are not compatible, and for this reason smartphones and other mobile devices have to implement dual radios to support both protocols.
Low Energy Audio Transmission
As its name suggests, LE Audio differs from Classic Audio in that it operates on the Bluetooth Low Energy radio. This is made possible by LE Isochronous Channels, a feature introduced in Bluetooth Core Specification version 5.2 that adds isochronous data transport on the Bluetooth Low Energy radio.
LE Audio will support the development of the same audio device types and use cases as Classic Audio. In addition, LE Audio introduces several key new features that will enable development of new device types and new use cases.
Not only does support for audio on LE allow for lower power consumption, it also enables the development of devices capable of both wireless data transfer and audio streaming using a single mode Bluetooth LE radio, rather than the current need to have dual radios. We however anticipate that mobile devices will still support Classic Audio for at least a few years, but that support will eventually be phased out.
High Quality Energy-Efficient Codec
LE Audio includes a new high-quality, low-power audio codec called LC3, or Low Complexity Communications Codec. Providing high quality even at low data rates, LC3 will bring tremendous flexibility to developers, allowing them to make better design tradeoffs between key product attributes such as audio quality and power consumption.
Source: Bluetooth SIG
The above graph shows results graded using ITU-R BS 1116-3 (PDF), which presents Methods for the subjective assessment of small impairments in audio systems:
4,o Perceptible, but not annoying
3.0 Slightly annoying
1.0 Very annoying
The SBC codec employed in Classic Audio scores a value of just above 4.0 at 345 kbits per second, whereas the LC3 codec scores higher, even with less than half the bitrate (160 kbps).
Enhanced User Experience
Developers can use LE Audio to enhance the user experience in several ways, starting with audio quality. Extensive listening tests show that LC3 provides superior audio quality over the SBC codec included with Classic Audio for typical use cases such as listening to music, even at a 50% lower bit rate. Developers can leverage the power savings provided by LE Audio to design products that provide longer battery life or, in cases where current battery life is enough, reduce the form factor by using a smaller battery.
LE Audio introduces Multi-Stream Audio, a new feature that enables the transmission of multiple, independent, synchronised audio streams between an audio source device and one or more audio sink devices. Using this new feature, developers can improve the performance of truly wireless earbuds, including a better stereo imaging experience, more seamless voice control services, and smoother switching between multiple audio source devices, such as when a headset is simultaneously connected to both a smartphone and laptop.
Classic Audio Streaming
In the relay (or forwarding) method employed by True Wireless Stereo (TWS) implementations in Classic Audio, the mobile device source first connects with the primary sink device using the standard Bluetooth Advanced Audio Distribution Profile (A2DP), which then relays the transmission to the secondary sink device for the other channel of the stereo pair. As well as the additional transmitter for the relay link, the primary sink device needs to provide data buffering to maintain synchronisation with the secondary sink, which in turn increases the overall link latency.
As well as being proprietary solutions and not part of the Bluetooth Core Specification, the added functional requirements for TWS sink device implementations represent increased material cost, weight and power consumption compared with the far more efficient and lower latency solutions offered by LE Audio Unicast and Broadcast isochronous streaming. Isochronous data transmission is time-sensitive and ensures a fixed phase relationship between two or more streams received by physically separate sink devices, such as wireless earbuds or speakers operating in stereo pairs.
Unicast Connected Isochronous Streams (CIS) enable the transfer of audio data between two devices with an acknowledgement scheme to provide flow control. An Asynchronous Connection-Oriented Link (ACL) control channel is used to set up the CIS stream and maintains the flow control until the stream is terminated.
A Connected Isochronous Group (CIG) contains one or more CIS streams, and in the case of multiple streams, these may flow in the same or opposite directions. The left and right channels of a stereo pair are each implemented as a CIS and contained within a CIG, each stream connecting directly to the wireless earbud, or other sink device, for that channel. The respective ACL flow controls ensure that both streams, being in the same direction, remain time-synchronised for the duration of the connection to maintain the stereo image. This allows the sink devices for the left and right channels of a stereo pair to operate independently and without any need to know about the existence of one another.
Auracast Broadcast Streaming
A name that will become very familiar in the near future, Auracast is Bluetooth SIG's trade name for LE Audio broadcast streaming. This technology enables multiple sink devices to connect to a single source in either mono or stereo.
Broadcast Isochronous Streams (BIS) are Connectionless in that they do not include ACL control channels to allow acknowledgements from sink devices back to the source device, and so a source device operating in Broadcast mode has no information about how many of a potentially unlimited number of receiving sink devices are subscribed to a BIS. Broadcasts can be configured to be open for any sink device to subscribe, or secured with a pass key to protect against unauthorised access.
As with Unicast connected streams, multiple BIS streams can be grouped together. The Broadcast Audio Source Endpoint (BASE) structure is a three tier hierarchy with the individual BIS streams as the bottom tier. At the middle tier, BIS streams with common features such as the left and right channels of a stereo pair are contained in Subgroups. The Subgroups are then aggregated into a Broadcast Isochronous Group (BIG) at the top tier.
The use of Unicast and Broadcast streams is not mutually exclusive in LE Audio, indeed implementations may switch between them, or use them in combination, to fulfil the requirements of a particular application.
Source: Bluetooth SIG
The LE Audio Opportunity
This is the beginning of a new wireless audio paradigm and an opportunity to create the enabling products that will revolutionise many aspects of our everyday lives.
As a Bluetooth SIG Adopter Member and an active participant in the development of LE Audio technology applications, Inline Audio is well placed to help companies gain a first mover advantage in the emerging market for LE Audio products. With our mutual non-disclosure agreement policy, companies can talk in confidence about realising this next generation of wireless products leveraging LE Audio technology. In conjunction with our manufacturing partner, we can provide a complete product development service from initial concept ideation to full-scale production shipment.
We aim to provide a variety of original content to promote the adoption of LE Audio across multiple market segments and user applications.
We will explore novel applications for LE Audio to inspire new and innovative product ideas, take a deep dive into the technical aspects, as well as share our own first-hand experience of LE Audio hardware and software development.
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