Summary
A guide to the LE Audio specifications by a former chair of the SIG's Hearing Aid Working Group, with chapters on broadcast, Presentation Delay and Auracast.
Key findings
- Section 2.2.8 expands LC3 as Low Complexity Communications Codec and describes it as the mandatory Bluetooth LE Audio codec. Section 3.3 describes encoding and decoding, and groups of streams with related timing, such as separate stereo channels.
- Section 4.4 describes broadcast isochronous streams (BIS) as one-way streams without a connection or receiver acknowledgements; receivers need the appropriate Broadcast_Code when a stream is encrypted. Section 4.4.1 (printed pp. 110–111) describes a Broadcast Isochronous Group (BIG) as one or more BISes and explains the timed intervals, anchor points and spacing of their transmissions.
- Chapter 12 describes Auracast as the Bluetooth SIG's brand for interoperable broadcast audio. Its introduction explains the Broadcast Assistant as a proxy user interface for the receiving device, potentially a phone application or another device, used to choose broadcasts.
- Discussing a TV heard through both its speakers and a hearing aid, states that a gap of much more than 30 to 40 ms between the stream and the room sound begins to be heard as echo, and that 30 to 40 ms is the sound travel time over about 10 m (section 2.1.1.2). No study is cited for the threshold.
- Presentation Delay can be set per transmitter in a large auditorium or stadium to offset the distance between each audience area and the sound source, as venues already do with loudspeaker delays (section 3.12).
- For broadcasts, values above 40 ms should generally be avoided because they may cause echo where room sound is present; the book calls alignment in large venues a fairly specialised use. The specifications do not say what a receiver should do with a Presentation Delay outside the range it supports.
- Reports that demonstrations of broadcast transmitters at 4 mW reached usable ranges of more than 50 m, without giving conditions (section 4.4).
- A phone acting as assistant may detect transmitters that are out of range of the user's earbuds, because its receiver is usually more sensitive (section 8.8.2).
Limits
The author's explanations, not a specification. The Broadcast Audio URI specification (2024) lists the author under GN Hearing A/S.
Read the original
www.bluetooth.com/wp-content/uploads/2025/01/Introduction-to-LE-Audio-2.0.pdf
Cited in
- Should the Auracast stream be delayed to line up with the loudspeakers?Open
- How do many transmitters share one broadcast across a large venue?Open
Cite this source
Nick Hunn. Introducing Bluetooth LE Audio, 2nd edition (including Auracast). Nick Hunn; free digital edition distributed by the Bluetooth SIG. November 2024. https://www.bluetooth.com/wp-content/uploads/2025/01/Introduction-to-LE-Audio-2.0.pdf (accessed 13 October 2026).
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