Auracast™ Simple Transmitter
Best Practices Guide
Technical Overview
This document provides recommendations to assist in the creationof uniform user experiences when designing and installingstandalone Auracast™ transmitter products.

Author: SIG Staff
Version: 2
Revision Date: 8 January 2024

Revision History

Version

Date

Changes1

3 October 2022

Initial Version

2

8 January 2024

Update to the initial version. Includes updated guidance
based on implementation feedback. Also includes guidanceon installer and administrator configuration settingsand documentation

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Table of Contents
1. Purpose of This Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1

Nomenclature6

1.2

Terminology		

6

1.2.1

PBP Broadcast Audio Stream Quality

6

1.2.1.2 High Quality Public Broadcast Audio7		

1.2.2 Auracast™ Transmitter Types

7		

1.2.2.1 Public Auracast™ Transmitter7		

1.2.2.2 Personal Auracast™ Transmitter7

1.2.3 Auracast™ Encryption

7		

1.2.3.1 Open Auracast™ Streams

7		

1.2.3.2 Closed Auracast™ Streams

8

1.2.4 General Bluetooth® LE Audio Stream Terminology

8

2. Auracast™ Transmitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1

Physical Implementations

9

2.2 Required Support for Standard Quality Public Broadcast Audio9

2.3 Basic Advertising Configuration

10

2.4 Using Metadata

11

2.5 Recommended Default Bluetooth® Settings

11

2.5.1 Auracast™ Broadcast Audio Related Data in		Primary Advertisements

12

2.5.2 Auracast™ Broadcast Audio Related Data in		Extended Advertisements13		

2.5.2.1 Public Broadcast Announcement Service (Mandatory) 13		

2.5.2.2 Broadcast_Name AD Type

14

2.5.3 Auracast™ Broadcast Audio Related Data in		Periodic Advertisements

15

		

15

2.5.3.1 Basic Audio Announcement

3Table of Contents		

2.5.3.2 Codec Specific Configurations

2.5.4 Broadcast_Code1818

2.6 Recommended Advertising Data Intervals

19

2.7 Additional Settings for a Public Auracast™ Transmitter20

2.8 User Configurable Fields

20

2.9 Advanced Design Settings for an Auracast™ Transmitter20

2.9.1 Output Transmit Power Level

21

2.9.2 Broadcast Audio Volume Level

21

2.9.3 Handling Stereo Audio21

2.10 Other Recommendations

22

3. Considerations for Installer and Administrator
Product Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1

Locating the Transmitter23

3.2 Configuring the Broadcast Transmitter23

3.3 Location Registration

24

4. Use of the Auracast Trademarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6. Appendix – Configuration Examples . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.1

Single stream mono Auracast™ transmitter28

6.1.1 BASE for a single stream mono Auracast™ transmitter28

6.1.2 Public Broadcast Announcement29

6.2 Stereo Auracast™ Transmitter30

6.2.1 BASE for a Stereo Auracast™ Transmitter30

6.2.2 Public Broadcast Announcement32

6.3 Three Channel Auracast™ Transmitter32

6.3.1 BASE for a three channel Auracast™ transmitter33

6.3.2 Public Broadcast Announcement

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1. Purpose of This Document
The purpose of this document is to provide guidance for developing, deploying, and documenting asimple, Auracast™ broadcast audio transmitter.
Broadcast audio is a new capability included in the Bluetooth® LE Audio set of specifications. It
allows multiple devices, which can be earbuds, hearing aids, headphones, or speakers, to receive
the same audio streams from a broadcast transmitter. These transmitters can support a variety ofaudio applications, ranging from low-latency voice to very high-quality music, as well as multiple
concurrent audio streams in different languages. The broadcast technology is designed for both
personal devices, such as smartphones, tablets, PCs, and domestic TVs, as well as public spaces,
like theatres, cinemas, churches, and hospitality venues. Unlike the inductive loop systems currently
installed for hearing aids, Bluetooth® LE Audio broadcast transmitters have the potential to bring ashared wireless audio experience to anyone with Auracast™ enabled earbuds or headphones.
To help ensure interoperability and a consistent user experience, the Bluetooth Special Interest Group(SIG) has created the Auracast™ brand program. This imposes certain requirements on broadcast
audio devices, including selected audio stream parameters which are common to all products.
Applying these requirements to broadcast audio devices helps ensure global interoperability between
all kinds of rendering devices and both public and personal Auracast™ transmitters.
Careful consideration about the configuration and deployment of an Auracast™ transmitter isrequired to ensure the best possible user experience for visitors to a location. This document provides
recommendations on settings to use when designing and installing an Auracast™ transmitter, as wellas suggestions on the instructions to provide to the person installing the transmitter at a location.
Broadcast audio is a one-way process at the transmitter, which needs to make autonomous decisions,
as it does not know how many devices are receiving its transmissions nor their capabilities. This
document describes a variety of typical, qualified implementations of Auracast™ transmitters to help
explain the decision process necessary to meet the Auracast™ broadcast audio requirements. It also
provides recommendations for some simple Auracast™ broadcast audio transmitters, utilizing the
Public Broadcast Source (PBS) role from the Public Broadcast Profile (PBP) specification [1].
This document is a tool which is dedicated to supporting broadcast of an audio input signal. Thereis no assumption made about the source of the audio signal (e.g., TV, A/V system, public address,
live audio, etc.). It is assumed that the broadcast transmitter can be configured by a user, but noassumption is made on how this is done. For example, it may be by a Bluetooth® link to a phone app, a
wired link, or an integrated user interface.
This document is not intended to provide an exhaustive description of the underlying Bluetooth®
specifications used in the creation of Auracast™ products; rather the goal is to provide a set ofclear, concise, and useful recommendations for product makers interested in building and deploying
Auracast™ transmitter products.

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1.1 Nomenclature
The Bluetooth® LE Audio specifications each ascribe different names for the roles taken by the threedevices that comprise the Auracast™ ecosystem. To help readability, this document uses the generic,descriptive names of Auracast™ transmitter, Auracast™ receiver and Auracast™ assistant. These
are used to describe both the physical devices and their roles. They are based on the definitionsof roles in the Basic Audio Profile, but also encompass the roles identified in various higher levelspecifications which are listed below:
Name

Includes the role ofSpecification

Auracast™ transmitter

Broadcast Source

BAP 2.2.2.1 [2]Public Broadcast Source

PBP 3.1 [1]Initiator

CAP 2.1.1 [10]Broadcast Media Sender

TMAP 3.5.2 [11]Broadcast Sink

BAP 2.2.2.2 [2]Public Broadcast Sink

PBP 3.2 [1]Acceptor

CAP 2.1.2 [10]Hearing Aid

HAP 3.2 [12]Broadcast Media Receiver

TMAP 3.5.2 [11]Broadcast Assistant

BAP 2.2.2.3 [2]Public Broadcast Assistant

PBP 3.3 [1]Commander

CAP 2.1.3 [10]Auracast™ receiver

Auracast™ assistant

1.2 Terminology
Auracast™ defines two new terms, which in turn are based on definitions of Standard and HighQuality (SQ and HQ) streams in Sections 4.2 and 4.3 of the Public Broadcast Profile (PBP). As they
are used extensively throughout this document, they are introduced here, along with relevant
terminology defined in PBP and other Bluetooth® LE Audio specifications.
1.2.1 PBP Broadcast Audio Stream Quality
The Public Broadcast Profile defines two sets of Audio Stream configurations which are exposed in
the Public Broadcast Announcement. They are:1.2.1.1 Standard Quality Public Broadcast Audio
Standard Quality Public Broadcast Audio streams are broadcast streams which are transmitted using
the LC3 codec [9] configurations that are mandatory for a Broadcast Sink to support in Table 6.4 of
Basic Audio Profile (BAP) [2]. By limiting them to configurations which every Broadcast Sink must
support, it ensures that Standard Quality Public Broadcast Audio streams can be received by every
Broadcast Sink. Within Auracast™ documents, they are referred to as SQ streams.

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These configurations include 16kHz and 24kHz sampling frequencies with 10ms frames, supporting
both low latency and high reliability use cases. The 16kHz option would normally only be used forvoice applications.
1.2.1.2 High Quality Public Broadcast AudioHigh Quality Public Broadcast Audio streams are broadcast streams which are transmitted using theLC3 codec configurations that are defined in Table 4.2 of PBP. Support for these is not mandated in
BAP or PBP, so some Auracast™ receivers will not be able to receive and render these streams. They
are included to accommodate devices which wish to use the highest 48kHz sampling rate supportedby the LC3 codec. These configurations use 48kHz sampling frequencies with 10ms frames,
supporting both low-latency and high-reliability use cases. Within Auracast™ documents, they arereferred to as HQ streams.
1.2.2 Auracast™ Transmitter Types
Auracast™ transmitters are classified in two categories based on the PBP Audio Stream category
they support:
1.2.2.1 Public Auracast™ Transmitter
A Bluetooth® product capable of transmitting a PBP-compliant Standard Quality (SQ) audio broadcast
and which is intended for deployment within a public venue, such as commercial public address (PA)systems, televisions, and audio streamers. A device claiming to be a Public Auracast™ transmittermust always transmit at least one Standard Quality Public Broadcast Audio Stream.
1.2.2.2 Personal Auracast™ Transmitter
A Bluetooth® product capable of transmitting a PBP-compliant audio broadcast which is intended for
personal use, such as a smartphone, tablet, laptop, PC, home television, or home audio streamer, may
be categorized as a Personal Auracast™ transmitter. Personal Auracast™ transmitters may default totransmitting a High Quality (HQ) Public Broadcast Audio stream but must allow the user to select aStandard Quality (SQ) broadcast audio stream so that they can be accessed by devices which are notcapable of decoding and rendering a 48kHz sampled stream. This may be accomplished by changing
to the lower sampling rates required for SQ or transmitting both HQ and SQ streams concurrently.
1.2.3 Auracast™ Encryption
Auracast™ broadcast audio uses the terminology Open and Closed to categorize devices which use
encryption for their broadcast streams.
1.2.3.1 Open Auracast™ Streams
Open Auracast™ streams are not encrypted and do not require a Broadcast_Code to render the
streams. It is recommended that Public Auracast™ transmitters are Open.

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1.2.3.2 Closed Auracast™ Streams
Closed Auracast™ streams are encrypted and require a Broadcast_Code to allow the received stream
to be rendered. Closed streams are typically the default for personal devices but may be used where
access to a public stream needs to be limited to a specific area, such as adjacent conference rooms
or screens in a cinema multiplex.
1.2.4 General Bluetooth® LE Audio Stream Terminology
The structure of broadcast streams is defined in the Bluetooth Core Specification [4]. Each audio
stream is carried in a Broadcast Isochronous Stream (BIS) and collections of related BISes areassembled into subgroups within a Broadcast Isochronous Group (BIG). Each BIS will normally carrya single stream, for example, left, right, or mono. The subgroups, which are defined in BAP [2], areused to collect together related BISes, such as streams in different languages or different codec
configurations. A BIG typically contains multiple BISes. Auracast™ receivers can decide which ofthese they wish to receive and ignore the rest based on their own configured preferences.

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2. Auracast™ Transmitters
This section provides a brief summary of the intended functions of an Auracast™ transmitter and therecommended configuration settings that may need to be exposed to the end user or installer of abasic Auracast™ transmitter.

2.1 Physical Implementations
Auracast™ transmitters may be installed by people with a wide range of technical knowledge,
from novice to expert. Manufacturers should design Auracast™ broadcast audio products with anunderstanding of the likely installer so that the end-user experience is the same when listening toan Auracast™ broadcast. A simple deployment or commissioning tool and a generic out-of-the-box
configuration should include enough information to provide a consistent user experience for theintended audience, along with the ability to tailor it with minimal technical knowledge.
The physical form factor of an Auracast™ transmitter is independent from its function. The Auracast™
transmitter might be a dongle that is plugged into an audio source, such as a phone, tablet, or PC, ora small box connected with a cable to the output jack of a sound system or TV (examples of both are
shown in Figure 2.1. It could equally be a System-on-Chip (SoC) or an embedded module integrating
Auracast™ functionality within a consumer electronics device, such as a smartphone, television,or PC.

OpticalHDMI ARC
3.5mm stereo jackor other audio input

LC3

LC3
Auracasttransmitter

Audio input
processing

USB/Lightning

Auracasttransmitter

Sound
Card

LC3

LC3

Figure 2.1 Examples of simple Auracast™ transmitters designed as adaptors or dongles

2.2 Required Support for Standard Quality Public Broadcast Audio
All Auracast™ transmitters are required to be able to transmit broadcast audio at 16kHz or 24kHz
using the LC3 codec [8]. This is a requirement to comply with the Auracast Trademarks in the Brand
Guide for Bluetooth Trademarks [3], which states that all transmitters must be configurable by the end
user to broadcast a Standard Quality Public Broadcast Audio stream.
Additionally, if the transmitter is marketed as being intended for use within a public location (where“public location” means any public, private, or commercial venue, building, means of transport, or
open space), the product’s default setting when configuring the product to transmit an Auracast™
broadcast must be to broadcast a Standard Quality Public Broadcast Audio stream.

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The intent of both of these requirements is to increase the likelihood that all products capable ofreceiving Auracast™ broadcast audio will be able to do so, as some resource-constrained devices,such as hearing aids, may only be capable of receiving Auracast™ broadcast audio that is configured
as a Standard Quality Public Broadcast Audio stream. In practice, what this means is, to support thebroadest portfolio of receiver devices in a public location, a Standard Quality Public Broadcast Audio
stream must be made available for all audio content provided through Auracast™ broadcast audio by
the location. Because the transmitted Standard Quality audio stream packets are smaller, they will
typically provide slightly better range and robustness to interference compared to High Quality (HQ)
packets.
In contrast, personal Auracast™ transmitters may default to transmitting an HQ audio stream but
are required to allow a user to select transmission of an SQ audio stream. If a standard-quality
audio stream is selected for transmission, the decision whether the SQ audio stream is transmitted
concurrently with a HQ audio stream, or is transmitted instead of a HQ audio stream, is determinedby the manufacturer1. It may also be user configurable.

2.3 Basic Advertising Configuration
All Bluetooth® LE Audio broadcasters use Extended and Periodic Advertisements to provide
information about their broadcast streams. Their use for Bluetooth® LE Audio is described in BAP [2]and PBP [1], and is illustrated in Figure 2.2.

Extended
Periodoc

Advertising Channels

Primary

ADV_EXT_IND
AD_Types
Appearance Value
Local Name

AUX_ADV_IND
AuxPtrBroadcast Audio Announcement (0x1852)(BAP)

Public Broadcast Announcement (0x1851)(PBP)

Broadcast_Name(PBP)

AUX_SYNC_IND
SyncInfo

BIGInfo (Core)

Basic Audio Announcement (0x1852)
BASE
Program_Info LTV
Language LTV

(BAP)
(BAP)
(AN)
(AN)

BIG

Figure 2.2 The location of Auracast™ broadcast audio related data in Primary, Extended, and Periodic advertisements
1

Concurrent transmissions of multiple streams may have an impact on airtime requirements and may require theuse of multiple BIGs.

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For Auracast™ transmitters, the PBP specification mandates inclusion of the Public Broadcast
Announcement within the Extended Advertisements that accompany an audio broadcast in addition
to the Broadcast Audio Announcement. The Public Broadcast Announcement informs devices looking
for broadcast audio streams whether the associated audio broadcast contains a Standard Quality
audio stream and/or a High Quality audio stream.
The information in the Public Broadcast Announcement is used to assist devices in determining
whether they should attempt to receive the associated periodic advertising data which gives themmore information about the broadcast audio streams. If the stream is not relevant, typically because
the rendering device does not have the resources to support an HQ stream, it can ignore it and moveon to find the next available transmitter. This reduces the overhead associated with having to retrieve
more detailed information from the periodic advertisements. It gives devices looking for broadcast
transmitters the ability to restrict scanning to just the streams they want to receive. By reading thecontents of the Public Broadcast Announcement, they can avoid streams which do not match
their requirements.

2.4 Using Metadata
To provide a good user experience, it’s important that Auracast™ transmitters provide enoughinformation about their streams to allow them to be unambiguously identified by a user. This isachieved by adding human-readable text strings in the Extended Advertising data and Periodic
Advertising data, using LTV2 structures that are defined in the specifications. [4]If metadata is applicable to all broadcast audio streams being transmitted, it should be included in the
Extended Advertising data. Metadata that is specific to a subset of audio streams being transmitted,
or which may change regularly, should be included in the Periodic Advertising data. The tables in
Section 2.5 show recommended settings for a public Auracast™ transmitter broadcasting a single
Broadcast Isochronous Group.

2.5 Recommended Default Bluetooth® Settings
This section shows the recommended default Bluetooth® settings for an Auracast™ transmitter.
These are defined in BAP [2] and PBP [1]. It lists the recommended data elements which an Auracast™
transmitter should include to ensure a good user experience and explains their usage. Eachrequirement is identified as being Mandatory (M), Recommended (R), Conditional (C), or Optional (O).
Auracast™ receivers and Auracast™ assistants which are scanning for this information will expect thepresence of items identified as Mandatory. In general, they will be able to provide an enhanced user
experience if Recommended and Optional items are also present in the Auracast™ transmissions.
Some of these values are set automatically as a result of the BIG configuration; others may be set by2

LTV stands for Length | Type | Value, which is a standard way of structuring data. The allowable LTV structures forBluetooth® LE Audio and Auracast™ applications are defined in the Assigned Numbers document [5].

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the manufacturer or the installer or end-user, depending on the use case. It is useful for a customer if some of these are printed on a labelon the Auracast™ transmitter, as users may need them to identify or configure the broadcaster. This is similar to the labelling on Wi-Fi
access points and broadband routers.
Parameters identified as user-defined are expected to be set when the Auracast™ transmitter is commissioned using an appropriate userinterface or application. They will normally be set to a default value at manufacture but may be overwritten by configuration applications
when they are installed.
2.5.1 Auracast™ Broadcast Audio Related Data in Primary Advertisements
There are two AD Types which are normally used in all Bluetooth® devices in the primary advertisements. Primary advertisements are theadvertisements that use the three fixed advertising channels of Bluetooth® LE, which also contain information about the existence
and location of Extended and Periodic advertisements. For Auracast™ devices, the following recommendations for the standard AD
Types apply.
AD TypeDefined in

Value

Local NameCSS [4]See
description

Requirement

Configurable

R

O

Description of usage
A user identifiable, unique name of the device, allowing the
Auracast™ transmitter to be identified during processes likepairing, for example, AcmeCorp-A4F7X9. This is normally set by
the manufacturer, but may be made configurable, allowing a user
or installer to update it.
Note that PBP Assistants use the Broadcast_Name for displaying
available Auracast™ transmitters, rather than the Local Name.

Appearance Value

Assigned
Numbers [5]0x0885RNo

The Appearance Value is intended to allow a user interface toselect an appropriate generic icon to identify a device. 0x0885 is a
generic broadcasting audio source.
Other values may be appropriate for specific applications. For
example, 0x0889 identifies an auditorium, 0x0040 a phone,
0x0881 a microphone, and 0x0A01 a television.
The values for the Appearance Value AD Type are defined in the
Assigned Numbers document [5].

Table 2.1 Auracast™ broadcast audio related data in primary advertisements

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2.5.2 Auracast™ Broadcast Audio Related Data in Extended Advertisements
The following Announcement UUIDs and AD Types are located in the Extended Advertisements. The tables in this section indicate
elements of each which should be considered for an Auracast™ transmitter implementation, but is not exhaustive. Implementers mustrefer to the BAP and PBP specifications for a complete list.
2.5.2.1 Public Broadcast Announcement Service (Mandatory)
The Bit value in the Public Broadcast Announcement Feature parameter, defined in Table 4.1 of the PBP specification [1], reflects the codec
configuration of the BIG that has been set in the Broadcast Audio Announcement, and the encryption status which is set in the BIGInfo.
Parameter
Public Broadcast
Announcement Service
Features [1](These bits are set by
the system based on theconfiguration of the BIG)

Metadata

Requirement
M

O

Audio_Active_State
Defined in Assigned Numbers Sect 6.12.6.10

Value

FeatureDescription of usage

Bit 0

Encryption

Set to 0b1 if the BISes are encrypted and 0b0 if they are not.
Note that all BISes in a BIG have the same encryption status. Either all are encrypted ornone are encrypted.

Bit 1Standard
Quality

Set to 0b1 if one or more of the BISes in the BIG are transmitted using the Standard
Quality settings. Mandatory for public Auracast™ transmitters.

Bit 2High Quality

Set to 0b1 if one or more of the BISes in the BIG are transmitted using the High
Quality settings.

All LTVs described below are optional.
The Audio_Active_State Metadata type is used to assist receiving devices in deciding
when to synchronise to a broadcast audio stream.
The Audio_Active_State Metadata should be included in the Public Broadcast
Announcement in Extended Advertising data if the broadcast audio content
is expected to be started or stopped on a regular basis. An example would beintermittent travel announcements at an airport or on a bus or train. If the broadcast
audio stream is not regularly interrupted, this LTV should be omitted.

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Broadcast_Audio_Immediate_Rendering_Flag

The Broadcast_Audio_Immediate_Rendering_Flag Metadata type is used to informreceiving devices that rendering the broadcast audio prior to the value of Presentation
Delay in the BASE may result in a better user experience. Because a broadcast
transmitter sets a value of Presentation Delay that it expects every device is to be able
to support, it may not be optimum, particularly if the listener can also hear audio fromlocal speakers.
Devices acting on the Broadcast_Audio_Immediate_Rendering_Flag will apply ashorter, manufacturer defined Presentation Delay value, reducing the overall latency,
in the expectation of providing a better listening experience.
The Broadcast_Audio_Immediate_Rendering_Flag should only be used where there
is a concern that the streamed audio may arrive later at the listener’s ear than direct
sound propagated through the air, which could result in an annoying echo or comb
filter effect.

Defined in Assigned Numbers Sect 6.12.6.11

Table 2.2 Auracast™ broadcast audio related data in Primary Advertisements in the Public Broadcast Announcement

2.5.2.2 Broadcast_Name AD TypeThe Broadcast_Name AD Type is the primary human readable text string used to identify the broadcast transmitter in user applications. It
may often be helpful to indicate the physical broadcasting device by making the Broadcast_Name string visible on the
Auracast™ transmitter.
AD Type
Broadcast Name [1]Requirement
M

Value

Description of usage

User
definedThe Broadcast Name should be set by the user when the Auracast™ transmitter is installed to describe its
identity in a form that will allow users to recognize and select it. Examples are: Lou’s Café, Conference
Room A, Gate 41B, TV3. This information is used by Auracast™ assistants to identify nearby Auracast™
transmitters in their User Interfaces. Its usage is similar to Wi-Fi SSIDs, but the Broadcast_Name contains
more relevant user information on the stream.
It is strongly recommended that this parameter is made available for a user or installer to set to an
appropriate name at installation, as described in the PBP specification. At shipment, the default should
be set to the same as the Local Name.
If multiple BIGs are transmitted by one Auracast™ device, the default values for each BIG should be
distinguished by the addition of a separate identifying character. (e.g. TV3-SQ, TV3-HQ)
If multiple transmitters are located in the same venue, carrying the same encoded audio content, theyshould use the same Broadcast_Name.

Table 2.3 Format of the Broadcast_Name for Auracast™ transmitters

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2.5.3 Auracast™ Broadcast Audio Related Data in Periodic Advertisements
2.5.3.1 Basic Audio Announcement
The Basic Audio Announcement (defined in Section 3.7.2.2 of BAP [2]) is transmitted in the Periodic Advertising Data. It includes the
Basic Audio Announcement UUID, followed by the Broadcast Audio Source Endpoint (BASE) structure, which defines the structure of
the Broadcast Isochronous Group (BIG), the arrangement of the individual Broadcast Isochronous streams (BISes) within it, and theirproperties. Examples of BASE structures are provided in the Appendix. The following table shows example values for some of the main
fields in the Basic Audio Announcement data structure. The Level column refers to the feature’s position in the BASE structure.
FeaturePresentation Delay

Level

Value

Requirement1

40,000M

Description of usage
Sets the Presentation Delay to 40ms, which is supported by all
Auracast™ devices.
If a lower latency is desired the Broadcast_Audio_
Immediate_Rendering_Flag can be included in the Public
Broadcast Announcement.

Codec_Specific_Configuration
Sampling Frequency

2
See Table 2.5

M

A public Auracast™ transmitter must transmit at least one BIS witha Codec_Specifc_Configuration that represents one of the 16_2_1,
16_2_2, 24_2_1 or 24_2_2 configurations from Table 6.4 of BAP. Fora public Auracast™ transmitter, the default QoS setting is generally
16_2_1 for voice applications and 24_2_1 or 24_2_2 for music. See
PBP [1] for more details. Personal Auracast™ transmitters may select a
codec configuration for one of the 48kHz option specified in PBP.

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Feature

Level

Value

Requirement

Number of Subgroups2

Normally 1 or 2

M

Number of BISes

2

Application
definedM

Description of usage

Many Auracast™ applications will have only one subgroup with eithera single mono BIS or two BISes representing left and right stereo
streams. If a hearing enhanced mono stream is available, this should
generally be transmitted as a third BIS, contained in a separate
subgroup from left or right streams. At least one Standard Quality
audio stream should be available for each independent audio input tothe transmitter.
Where both 24kHz and 48kHz audio streams are being simultaneouslytransmitted, these are enabled as separate subgroups, or as separate
BIGs. The choice is largely dependent on the airtime requirements.
The use of multiplexed streams is discouraged, as their support is notmandated in HAP or PBP and they will increase the power consumptionof hearing aids and earbuds compared to using individual BISes foreach stream.

Level 2 Metadata
Streaming_Audio_Contexts LTV

2Level 2 metadata applies to all BISes in that subgroup.
Application
dependentR

If supported, this field should reflect the use case, which may bebased on the implementation, the intended application, or be user
configurable. Typical values are Live for microphone inputs, orMedia where the audio is output with video, such as a TV, cinema,or is a music stream. In most cases, this will be selected at the initialcommissioning, but more complex devices may set this automatically.
Auracast™ transmitters designed for general purpose deployment may
also use the Unspecified option.
The values for the Streaming_Audio_Contexts LTV are defined in the
Assigned Numbers document [5].

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Program_Info LTV

Application
dependentR

If supported, this LTV provides metadata describing the current audio
stream. It is often dynamic data which is updated by metadata inincoming content, for example, from a TV’s EPG data. It may also be
configurable by a user.
The values for Program_Info LTV may differ across subgroups.
For example, if two subgroups contain audio streams in different
languages, this may be reflected in the language strings for the
Program_Info LTVs.

FeatureLevel

Language LTV [5]Value
Application
dependent

Requirement
R

Description of usage
This should be set to reflect the language, where that information
is known. For simple Auracast™ transmitters, which only have an
audio input, with no metadata to identify the language used, it can beomitted. The value applies to all BISes in that subgroup.
The values for the Streaming_Audio_Contexts LTV are defined in the
Assigned Numbers document [5].

Codec_Specific_Configuration
Audio_Channel_Allocation LTV

3Implementation
dependentC

Set to indicate at which audio location each stream is intended tobe rendered. This is used by Auracast™ receivers and Auracast™
assistants to select the correct audio streams.
In most Auracast™ use cases, the following values should be used:
0x00000001 – Left (Front Left)
0x00000002 – Right (Front Right)
The Audio_Channel_Allocation LTV shall be present unless the stream
is mono / unspecified, in which case no Audio_Channel_Allocation
LTV shall be present in the Codec_Specfication_Configuration ateither Level 2 or Level 3.
The use of multiplexed stereo streams is not recommended, as it
results in unnecessary power consumption on Auracast™ receivers
which only render a single audio stream.

Table 2.4 Auracast™ broadcast audio related data in the Broadcast Audio Announcement and BASE

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2.5.3.2 Codec Specific Configurations
A Public Auracast™ transmitter must transmit at least one BIS with a Codec_Specifc_Configuration that represents one of the 16_2_1,
16_2_2, 24_2_1 or 24_2_2 configurations from Table 6.4 of BAP.
LTV Structure

16_2_1 / 16_2_2

24_2_1 / 24_2_2

Codec_ID (LC3 Coding Format)

0x06

0x06

Sampling_Frequency LTV

16000 kHz

24000 kHz

Frame_Duration

10 ms

10 ms

Octets_Per_Codec_Frame

40 octets

60 octets

Table 2.5 Codec Configuration settings for public Auracast™ transmitters

2.5.4 Broadcast_Code
If the Auracast™ streams are encrypted, the encryption bit of the Public Broadcast Announcement will be set, and a Broadcast_Codemust be made available to users. The value of the Broadcast_Code for a public Auracast™ transmitter is generally static for the life of thedevice. For personal Auracast™ transmitters, the Broadcast_Code may be changed at the start of each new session, i.e., whenever the
BIG is started. In this case a mechanism needs to be provided to communicate this change to the user’s devices.
Public Auracast™ devices do not normally support encryption, in which case no value is set for Broadcast_Code.
FeatureValue

Requirement

Broadcast_Code

Factory
default

M for encrypted
streams

Configurable
R

Description of usage
The factory default value of Broadcast_Code should be a unique string that a user
can input into an Auracast™ assistant, comprised of between 4 and 16 characters.
Recommendations on allowable characters are given in the Core Vol 3, Part C,
Section 3.2.3.3. The Broadcast_Code should be different to any other password
or access code used on the device.
The Broadcast_Code may be a fixed string, supplied with the device, a user
configurable string, or a code which can change with each session. The factory
default value should be provided with the device.
Personal Auracast™ devices are likely to change the Broadcast_Code on a
per session basis. Where session based codes are used, a mechanism must be
provided to inform the user of each new value. This is implementation specific.

Table 2.6 Broadcast_Code requirements for Auracast™ transmitters18

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For most public Auracast™ transmitters, the Broadcast_Code is supplied to the user using an Out ofBand method. This will often be accomplished by a public display of the code, which a user can enterusing an application on an Auracast™ assistant, which will convey it to the Auracast™ receiver. An
example of a simple, printed notice is shown below.

Broadcast Details for Tonight's Event
Auracast™ Broadcast: Mark's Tasting Evening
Passcode: PinotNoir

Figure 2.3 Example of a public Auracast™ broadcast audio notice with a Broadcast_Code

Auracast™ transmitter manufacturers should be aware of the constraints of Auracast™ assistants
that are on the market in their intended sales geographies, which may have language specificinput requirements.

2.6 Recommended Advertising Data Intervals
The advertising intervals used for Extended Advertising and Periodic Advertising should be chosenwith regard to the speed of acquisition that best suits the use case. Setting the values too high will
increase the time between advertisements, which may increase the time it takes for a device todiscover and acquire a broadcast audio stream, causing it to expend unnecessary power.
For example, a personal Auracast™ transmitter, such as a phone, might be used to provide a sharedaudio experience to a small group of friends. In this use case, the acquisition time of the broadcast
audio need not be immediate, as the phone owner can tell them that the transition to broadcast is
in progress. Designers of earbuds, hearing aids, speakers, and headphones as well as Auracast™
assistants need to consider the user experience and how it will reflect these trade-offs.
In a typical use case, a receiving device using a scanning interval of 1.28s (the period between
the start of consecutive scans), and a scanning window of 11.25ms (the length of the scan) should
normally be able to acquire Extended Advertising data sent at 30ms intervals within 8 seconds with
95 percent confidence. The period and length of the scan used by the receiving device can have asignificant impact on power consumption of the device and the transmitting device should attempt toprovide this data as frequently as possible within its own power budget to both maximize the speedof acquisition and minimize the power consumption of the receiver. To preserve battery, scanning will
normally only take place as a result of a user action, and should cease after 30 – 60 seconds, unlessrefreshed by the user.
Table 2.7 shows recommended Bluetooth® settings for the broadcaster’s advertising data. Thesesettings help scanning devices discover the presence of Auracast™ broadcast audio streams in atimely manner.

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FeatureValue

Extended Advertising data interval

30ms

Table 2.7 Recommended values for advertising the presence of a public Auracast™ transmitter

2.7 Additional Settings for a Public Auracast™ Transmitter
In additional to the information described above, Table 2.8 shows recommendations for Bluetooth® LE characteristics for an Auracast™
transmitter. These characteristics, which are part of the Device Information Service (DIS) [9], enable a user to identify the transmitter for
maintenance and commissioning. These are included as a reminder of good practice to help installers configure and maintain products
and are not specific Auracast™ requirements. If the features in Table 2.8 are made accessible through the Bluetooth® LE characteristics, itallows their use in diagnostic and configuration applications which may help the installer. These characteristics are defined in the Device
Information Service [9].
FeatureDescription

UUID1

Value

Printed on label

Configurable

Manufacturer Name String

Name of manufacturer

0x2A29Product specific

YES

NO

Model Number String

Name of the specific model

0x2A24

Product specific

YES

NO

Serial Number String

Unique Serial Number

0x2A25

Product specific

YES

NO

1. UUIDs are defined in the Assigned Numbers document [5].
Table 2.8 General settings for a public Auracast™ transmitter

2.8 User Configurable Fields
It is good practice to protect any user configurable fields by implementing a username and password that needs to be entered to accessthe configuration utility before any changes to the settings can be made. This should be independent of the method used to access theconfiguration application, which may be a wired or wireless connection depending on the device implementation.

2.9 Advanced Design Settings for an Auracast™ TransmitterThis section discusses implementation decisions which should be considered during the specification and design of an
Auracast™ transmitter.

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2.9.1 Output Transmit Power Level
The transmitter should provide the ability to configure the output power level. At its simplest, thetransmitter may provide a Low, Medium or High transmit power setting. This setting helps installers
optimize the transmitter power for the size of the intended coverage area, good coexistence withother uses of the 2.4 GHz band (e.g., Wi-Fi networks) and any signal obstructions in the coverage area
(thick walls, metal structures, water, etc.).
It is possible to design an Auracast™ transmitter that satisfies regulations worldwide to transmit atan output power up to +20 dBm. Care must be taken at both application and chipset level to comply
with all applicable regulatory requirements for operation in the 2.4 GHz band, which differ between
markets (North America, the European common market, Japan, China, etc.). For more information
please refer to the Bluetooth® Low Energy Regulatory Aspects Document (RAD), published by theBluetooth SIG.
2.9.2 Broadcast Audio Volume Level
Having a common reference level for the signal in an Auracast™ transmission is important to secure
the best user experience when switching to Auracast™ streaming. The Auracast™ transmitter should
therefore operate at the reference level which is a long-term average level of -35 dB FS, equivalent to
70 dB SPL and a maximum level of -3 dB FS. If needed, end users can adjust the personal volume level
for their device, either directly on the device, or using a personal remote control or application.
These values are derived from the reference levels for inductive loop systems, EBU standards andcomparisons to other input sources in hearing aids. The 70 dB SPL reference level at -35 dB FS meansthat levels up to 102 dB SPL can be transmitted in Auracast™ broadcast audio, which should be finefor most situations except live events where the SPL can go above 102 dB SPL. The LC3 [8] codec canhandle a dynamic range of 115 dB because of the 24-bit internal signal representation in the codec,
but if it is configured for 16 bits, the useful dynamic range will be limited to around 90 dB. Setting thereference level to -35 dB FS, while maintaining the -3 dB FS as the maximum allows transmissions up
to 102 dB SPL while still maintaining a good signal to noise ratio.
In some use cases, it may be necessary to adjust the default audio reference signal level of thetransmitter to a level other than 70 dB SPL to achieve optimum performance, but this will normally belimited to professional installations.
2.9.3 Handling Stereo Audio
Bluetooth® LE Audio was designed to minimize the power demands of hearing aids and earbuds sothat they can maximize their battery life. An important factor in achieving that is that Auracast™
transmitters should only send them the data that they need to render. Where the Bluetooth® Classic
A2DP profile transmits joint stereo streams to devices, Bluetooth® LE Audio can send independent
left and right streams so that each earbud only needs to listen for a shorter amount of time. The
Bluetooth® LE Audio specification allows a device to transmit a multiplexed stereo stream, but it is notmandatory for a BAP or PBP compliant receiver to be able to receive or decode it.

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For this reason, Auracast™ transmitters should not transmit multiplexed audio streams as their
only transmission.
Auracast™ transmitters should not assume that receiving devices are capable of performing stereo
to mono conversion. This would require them to receive two audio streams and perform additional
processing. As an Auracast™ transmitter will almost always have more resources, especially in termsof power, the Auracast™ transmitter should process the stereo stream locally and then transmit aseparate mono stream. This means that any such transmission is only done once.
Depending on the application, Auracast™ transmitters may wish to include a configuration option toconvert an incoming stereo signal to mono only, particularly if the intended recipients of the stream
are hearing aids. Examples may be live audio at a lecture, conference room, or classroom.

2.10 Other Recommendations
This document covers the use case of individual Auracast™ transmitters. If Auracast Trademarks are
publicly displayed, other recommendations and/or requirements may apply.

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3. Considerations for Installer and Administrator
Product Documentation
This section includes guidance that a manufacturer may wish to include in their productdocumentation to guide administrators and installers through the commissioning process. It is notintended that these are reproduced exactly, but the areas described below should be covered toensure the best user experience.

3.1 Locating the Transmitter
To provide your visitors with a good Auracast™ broadcast audio experience within the intended
coverage area, it is essential to choose the best location for the transmitter. Please follow these basic
guidelines when deciding where to place the Auracast™ transmitter:•

Centralize: Install the transmitter in a location that is as central as possible within the intended
coverage area.

•

Height: Install the transmitter in the highest possible location relative to the habitable area of thevenue, ideally on a ceiling, lowest high beam, or high on a wall.

•

Avoid obstructions: Install the transmitter in a location that is free from obstructions, such as
beams, rafters, or other electrical equipment. Avoid installing the transmitter within enclosures
such as cupboards, or behind metal partitions or counters.

3.2 Configuring the Broadcast TransmitterTo ensure the best visitor experience, please customize the following broadcast
configuration settings:•

Broadcast Name: It is important to name the broadcast so that visitors can easily identify its
contents and differentiate it from other broadcasts that may be available in the same area. This
is normally achieved using a user configuration process or application which should be suppliedwith the Auracast™ transmitter. For example, if the transmitter is being used with a public
television, the Broadcast Name should be set to help visitors identify it as TV audio as well as to
identify the correct TV with which it is associated (e.g., “Strikers Pub TV1”, “Strikers Pub TV2”,etc.). If the transmitter is being used with a PA system in a hotel conference room, the broadcast
name should help the user identify the correct room with which the broadcast is associated (e.g.,“Hilton Ballroom Audio”, “Hilton Boardroom Audio”, etc.).

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Broadcast Quality: Auracast™ broadcast audio supports two audio quality levels, Standard
Quality and High Quality. Not all receiving devices (e.g., hearing aids) can receive High Quality
broadcasts. In public locations, the transmitter should default to Standard Quality. If the location
wishes to promote the availability of Auracast™ broadcast audio, they are required to makeavailable a Standard Quality version of any audio.

•

Broadcast Security: Auracast™ broadcasts can be configured to be Open, where anyone with
an Auracast™ receiver will be able to join, or Closed (encrypted), where visitors will be required
to enter the Broadcast_Code string to join the broadcast. In situations where the transmitter isbeing installed in a public location, it is likely the broadcast will be configured to be Open andnot require a Broadcast_Code. In those situations where the broadcast needs to be Closed, youwill need to set a Broadcast_Code as well as implementing a method for the location to share theBroadcast_Code with authorized users. If registered as an Auracast™ location with encryption
enabled, the Broadcast_Code should be displayed in a prominent location to help end users
discover and join an Auracast™ broadcast audio stream.

•

Broadcast Range: You can adjust the power level of the transmitter to adjust its coverage area.
The higher the power level, the larger the physical area it will cover. The best practice is to set
the power level to the lowest level that meets the intended coverage area. Determining thecorrect power level to use may take some experimentation. It is recommended that you start byconfiguring the broadcast to the lower power level and then use an Auracast™ receiver to walkthroughout the intended coverage and test the audio quality. If the quality of reception is not
sufficient, increase the power to the next higher level and retest the area. Continue this processuntil the audio reception is consistent throughout the intended coverage area. Be aware that thepresence of people in the room and the location of the transmitter may affect the range, so repeat
the coverage check when the room is being used or the transmitter location has changed. Placing
the Auracast™ transmitter above head level will minimize this effect.

After installation and commissioning, the broadcast transmissions should be checked with earbuds orheadphones. It is recommended that for installations where no speakers are included, regular checks
should be made to confirm that broadcasts are available for public reception.
We hope these guidelines will help you provide the best possible Auracast™ broadcast audio
experience for visitors to your location.

3.3 Location Registration
Once you have installed an Auracast™ transmitter for public use, you are encouraged to register
the location with the Bluetooth SIG using the Auracast Location Registration Tool. Registering yourlocation will allow you to show your support of Auracast™ broadcast audio to the global communityof consumers looking for audio accessibility and new audio experiences in public spaces. Locations
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Appear in an upcoming, consumer-searchable database of Auracast™ broadcast audio locations,managed by the Bluetooth SIG.

•

Receive a welcome packet of brand resources for your location, including a window sticker for
you to display.

•

Gain additional access to .to the Auracast Trademarks and promotional materials.Stay up-to-dateon necessary requirements to ensure global accessibility of Auracast™
broadcast audio.

The Bluetooth SIG encourages public locations who have completed the registration process
and met the licensing requirements to use the Auracast Trademarks to promote the availability of
Auracast™ broadcast audio at their locations, on their websites, and throughout theirpromotional materials.

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4. Use of the Auracast Trademarks
Use of the Auracast word mark, figure mark, and combination mark (collectively, the Auracast
Trademarks) is only permitted under license from the Bluetooth SIG. Licensees may use the Auracast
Trademarks in association with products that have completed the Bluetooth® Qualification Process
and indicated in the submission to the Bluetooth® Qualification Process that the products implement
and meet the requirements for the Public Broadcast Source (PBS) role, the Public Broadcast Sink
(PBK) role, or the Public Broadcast Assistant (PBA) role as defined in the Public Broadcast Profile(PBP) Specification.
The requirements of use for the Auracast Trademarks are located in the Brand Guide for Bluetooth
Trademarks. This guide can be found on the bluetooth.com website:
https://www.bluetooth.com/develop-with-bluetooth/marketing-branding/In addition to detailing the licensing requirements for using the Auracast Trademarks, the Public
Location Brand Guide for Auracast Trademarks [7] also provides rules and guidelines when displaying
the Auracast Trademarks at your location and in supporting promotional materials.

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5. References[1] Public Broadcast Profile, version 1.0 or later[2] Basic Audio Profile 1.0 or later[3] Brand Guide for Bluetooth Trademarks[4] Core Specification Supplement, version 10 or later[5] Assigned Numbers[6] Bluetooth® Core Specification, version 5.2 or later[7] Public Location Brand Guide for Auracast Trademarks[8] Low Complexity Communication Codec (LC3), version 1.0 or later[9] Device Information Service[10] Common Audio Profile[11] Telephony and Media Audio Profile[12] Hearing Access Profile

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6. Appendix – Configuration Examples
This appendix contains examples of the BASE structure within the Broadcast Audio Announcement (seeSection 2.5.3.1) and Public Broadcast Announcements (see Section 2.5.2.1) for a variety of common
Auracast™ transmitter implementations.

6.1 Single stream mono Auracast™ transmitterThis example is for a simple transmitter which has a single, mono audio input. A typical
implementation is a broadcast microphone, which could be a handheld microphone with an
integrated Auracast™ transmitter. The device and its BASE structure are illustrated in Figure 6.1.
Level 1 - BIG
Presentation Delay
Number of BIS Subgroups

Level 2 - BIS Subgroup 0
LC3

Number of BISes in the Subgroup
Codec Information
Stream Metadata

Auracast
Transmitter

Microphone

Level 3 - BIS [0(0)]BIS_Index 0x01
Figure 6.1 Example implementation and BASE structure for a mono Auracast™ transmitter

6.1.1

BASE for a single stream mono Auracast™ transmitter

The following table shows an example of a BASE for the single stream mono Auracast™ transmitter
described above.
Level Parameter

Size(Octets)

Length1

Length of Type and Value fields for AD data type:
0x1E = 30 octets

Type: «Service Data - 16-bit UUID»

1

0x16 (Defined in Bluetooth® Assigned Numbers [5])

Value

1

Value and Description(2-octet Service UUID followed by additional
service data)

Basic Audio Announcement Service
UUID

2

0x1851 (Defined in Bluetooth® Assigned
Numbers [5])Presentation_Delay

3

40 ms

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Size(Octets)

Level Parameter

Value and Description

1

Num_Subgroups

1

0x01: 1 Subgroup

2

Num_BIS[0]10x01: 1 BIS in Subgroup[0]2Codec_ID[0]5Octet 0: 0x06 = LC3 Coding_Format
Octet 1–2: 0x0000
Octet 3–4: 0x0000

2

Codec_Specific_Configuration_
Length[0]1Length of the Codec_Specific_Configuration for
Subgroup[0]: 10 octets – 0x0A

2

Codec_Specific_Configuration[0]10

3 LTV structures for Subgroup[0] defining:
LTV 1: Sampling_Frequency: 24000 Hz
LTV 2: Frame_Duration: 10 ms
LTV 3: Octets_Per_Codec_Frame: 60 octets

2

Metadata_Length[0]1Length of Subgroup[0] Metadata: 4 octets

2

Metadata[0]41 LTV structure for Subgroup[0], defining:
LTV 1: Streaming_Audio_Contexts [0x02]:
Live 0x0040

3

BIS_index[0[0]]

1

0x01

Note that there is no Audio_Channel_Allocation LTV structure in the Level 2 or 3 Cocec_Specific_Configuration, as thestream is Mono.
Table 6.1: BASE entries for example of a mono Auracast™ transmitter as shown in Figure 6.1.

6.1.2 Public Broadcast Announcement
Table 6.2 shows the values for the Public Broadcast Announcement for this example, which istransmitted in the Extended Advertisements.
In this example, the optional metadata includes the Broadcast_Audio_Immediate_Rendering_Flag,
which informs Broadcast Receivers that they can ignore the value of Presentation Delay if they areable to render the audio earlier.
Parameter

Size(Octets)

Value

Description

Length7

0x07

Length of Type and Value fields for AD data type

Type: «Service Data»

1

0x16

16 bit UUID Service Data [5]Value

2-octet Service UUID followed by additional service data29

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Parameter

Size(Octets)

Value

Description

Public Broadcast
Announcement
Service UUID

2

0x1856

Defined in Bluetooth® Assigned Numbers [5]Public Broadcast
Announcement
features1

0x02

Bit 0 = 0b0 (Not encrypted)
Bit 1 = 0b1 (Standard Quality present)
Bit 2 = 0b0 (High Quality not present)

Metadata_Length

1

0x02

Length of the Metadata field

Metadata

20x01

LTV structure defining:

0x09

LTV 1: Broadcast_Audio_Immediate_Rendering_Flag (0x09)

Table 6.2: Advertising data format for the Public Broadcast Announcement shown in Figure 6.1.

6.2 Stereo Auracast™ TransmitterThis example is for a Auracast™ transmitter in the form of a dongle which transmits a stereo signal as
two separate BISes – one for left and one for right. It could be plugged into a phone or PC to provide
a stereo broadcast stream. The device and its BASE structure are illustrated in Figure 6.2.

Level 1 - BIG
Presentation Delay
Number of BIS Subgroups (1)Level 2 - BIS Subgroup 0

LC3

USB/Lightning

Auracast™
Transmitter

Sound
Card
LC3

Number of BISes in the Subgroup (2)Codec Information
Stream Metadata

Level 3 - BIS [0(0)]Level 3 - BIS [0(1)]BIS_Index 0x01
Channel (L)BIS_Index 0x02
Channel (R)Figure 6.2 Example implementation and BASE structure for a stereo Auracast™ dongle

6.2.1 BASE for a Stereo Auracast™ Transmitter
The following table shows an example of a BASE for the stereo stream Auracast™ transmitter
described above.

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Level

Parameter

Size(Octets)

Length1

Length of Type and Value fields for AD data type:0x2D = 43 octets

Type: «Service Data - 16-bit UUID»

1

0x16 (Defined in Bluetooth® Assigned Numbers [5]

Value

Value and Description

2-octet Service UUID followed by additional
service data

Basic Audio Announcement Service
UUID

2

0x1851 (Defined in Bluetooth® Assigned
Numbers [5])1

Presentation_Delay

3

40 ms

1

Num_Subgroups

1

0x01: 1 Subgroup

2

Num_BIS[0]10x02: 2 BISes in Subgroup[0]]2Codec_ID[0]5Octet 0: 0x06 = LC3 Coding_Format
Octet 1–2: 0x0000
Octet 3–4: 0x0000

2

Codec_Specific_Configuration_
Length[0]1Length of the Codec_Specific_Configuration for
Subgroup[0]: 10 octets - 0x0A

2

Codec_Specific_Configuration[0]10

3 LTV structures for Subgroup[0] defining:
LTV 1: Sampling_Frequency: 24000 Hz
LTV 2: Frame_Duration: 10 ms
LTV 3: Octets_Per_Codec_Frame: 60 octets

2

Metadata_Length[0]1Length of Subgroup[0] Metadata: 6 octets

2

Metadata[0]41 LTV structure for Subgroup[0], defining:
LTV 1: Streaming_Audio_Contexts: Media3

BIS_index[0[0]]

1

0x01

3

Codec_Specific_Configuration_
Length[0[0]]1

Length of the Codec_Specific_Configuration for
BIS_index 0x01: 0x06 octets

3

Codec_Specific_Configuration[0[0]]6

1 LTV structure for BIS_Index 0x01, defining:
LTV 1 = Audio_Channel_Allocation: FL

3

BIS_index[0[1]]

1

0x02

3

Codec_Specific_Configuration_
Length[0[1]]1

Length of the Codec_Specific_Configuration for
BIS_index 0x02: 0x06 octets

3

Codec_Specific_Configuration[0[1]]6

1 LTV structure for BIS_Index 0x02, defining:
LTV 1 = Audio_Channel_Allocation: FR

Table 6.3: BASE structure for the example shown in Figure 6.2.

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6.2.2 Public Broadcast Announcement
Table 6.4 shows the values for the Public Broadcast Announcement for this example, which istransmitted in the Extended Advertisements.
Parameter

Size(Octets)

Value

Description

Length4

0x04

Length of Type and Value fields for AD data type

Type: «Service Data»

1

0x16

16 bit UUID Service Data

Value

2-octet Service UUID followed by additional service data

Public Broadcast
Announcement
Service UUID

2

0x1856

Defined in Bluetooth® Assigned Numbers [5]Public Broadcast
Announcement
features1

0x02

Bit 0 = 0b0 (Not encrypted)
Bit 1 = 0b1 (Standard Quality present)
Bit 2 = 0b0 (High Quality not present)

Metadata_Length

1

0x00

No Metadata

Table 6.4: Advertising data format for the Public Broadcast Announcement as shown in Figure 6.2.

6.3 Three Channel Auracast™ TransmitterThis example is for an Auracast™ transmitter in the form of module for a TV or set-top box, which isdesigned to simultaneously transmit a stereo channel comprising a Left and Right BIS, along with amono channel containing dialogue enhanced audio for a listener with hearing loss. The Streaming_Context_Type is set to Media.
A similar device is also applicable to theatres and similar venues, where audio streams areproduced for audience members both with and without hearing issues. For these applications, theStreaming_Contexts_Type should be set to “Live” rather than “Media”, as ambient sound will beavailable alongside the Bluetooth® stream. As “Live” use cases generally benefit from lower latencies,
the Broadcast_Audio_Immediate_Rendering_Flag should be included in the Public Broadcast
Announcement metadata section.
Although the Hearing Enhanced stream contains the same content and is rendered at the same time,
it is placed into a separate subgroup. This allows it to be identified by an Auracast™ assistant using
the Assisted Listening Stream LTV in the Level 2 stream metadata.
The device and its BASE structure are illustrated in Figure 6.3.

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Level 1 - BIG
Presentation Delay
Number of BIS Subgroups (2)

Left

LC3

Right

LC3

Assisted
Listening

LC3

Auracast™
Transmitter

Level 2 - BIS Subgroup 0

Level 2 - BIS Subgroup 1

Number of BISes in the Subgroup (2)Codec Information
Stream Metadata

Number of BISes in the Subgroup (1)Codec Information
Stream Metadata

Level 3 - BIS [0(0)]Level 3 - BIS [0(1)]Level 3 - BIS [1(0)]BIS_Index 0x01
Channel (L)BIS_Index 0x02
Channel (R)BIS_Index 0x01

Figure 6.3 Example implementation and BASE structure for a stereo Auracast™ dongle

6.3.1 BASE for a three channel Auracast™ transmitter
The following table shows an example of a BASE for the three channel Auracast™ transmitter
described above.
Level

Parameter

Size(Octets)

Length1

Value and Description
Length of Type and Value fields for AD data
type: 0x47 = 71 octets

Type: «Service Data - 16-bit UUID»

1

Value

0x16 - Defined in Bluetooth® Assigned
Numbers [5](2-octet Service UUID followed by additional
service data)

Basic Audio Announcement Service UUID

2

0x1851 (Defined in Bluetooth® Assigned
Numbers [5])1

Presentation_Delay

3

40 ms

1

Num_Subgroups

1

0x02: 2 Subgroups2

Num_BIS[0]10x02: 2 BISes in Subgroup[0]2Codec_ID[0]5Octet 0: 0x06 = LC3 Coding_Format
Octet 1–2: 0x0000
Octet 3–4: 0x0000

2

Codec_Specific_Configuration_Length[0]1Length of Subgroup[0] Metadata: 4 octets

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Level
2

Parameter
Codec_Specific_Configuration[0]Size(Octets)
10

Value and Description
3 LTV structures for Subgroup[0] defining:
LTV 1: Sampling_Frequency: 24000 Hz
LTV 2: Frame_Duration: 10 ms
LTV 3: Octets_Per_Codec_Frame: 60 octets

2

Metadata_Length[0]1Length of Subgroup[0] Metadata: 4 octets

2

Metadata[0]41 LTV structure for Subgroup[0], defining:
LTV 1: Streaming_Audio_Contexts: Media3

BIS_index[0[0]]

1

0x01

3

Codec_Specific_Configuration_Length[0[0]]1

Length of the Codec_Specific_Configurationfor BIS_index 0x01: 0x06 octets

3

Codec_Specific_Configuration[0[0]]6

1 LTV structure for BIS_Index 0x01, defining:
LTV 1 = Audio_Channel_Allocation: FL

3

BIS_index[0[1]]

1

0x02

3

Codec_Specific_Configuration_Length[0[1]]1

Length of the Codec_Specific_Configurationfor BIS_index 0x02: 0x06 octets

3

Codec_Specific_Configuration[0[1]]6

1 LTV structure for BIS_Index 0x02, defining:
LTV 1 = Audio_Channel_Allocation: FR

2

Num_BIS[1]10x01: 1 BIS in Subgroup[1]2

Codec_ID[1]5Octet 0: 0x06 = LC3 Coding_Format
Octet 1–2: 0x0000
Octet 3–4: 0x0000

2

Codec_Specific_Configuration_Length[1]1Length of the Codec_Specific_Configurationfor Subgroup[0]: 10 octets

2

Codec_Specific_Configuration[1]10

3 LTV structures for Subgroup[1] defining:
LTV 1: Sampling_Frequency: 24000 Hz
LTV 2: Frame_Duration: 10 ms
LTV 3: Octets_Per_Codec_Frame: 60 octets

2

Metadata_Length[1]1Length of Subgroup[0] Metadata: 7 octets

2

Metadata[1]262 LTV structures for Subgroup[1], defining:
LTV 1: Streaming_Audio_Contexts: MediaLTV2: Assisted Listening Stream3

3

BIS_index[1[0]]

1

0x03

Note that there is no Audio_Channel_Allocation LTV structure in the Codec_Specific_Configuration at Levels 2 or 3 for
Subgroup[1], as the stream is Mono.
Table 6.5: BASE structure for the logical BASE structure example shown in Figure 6.3.

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6.3.2 Public Broadcast Announcement
Table 6.6 shows the values for the Public Broadcast Announcement for this example, which istransmitted in the Extended Advertisements.
Size(Octets)

Value

Description

Length4

0x04

Length of Type and Value fields for AD data type

Type: «Service Data»

1

0x18

16 bit UUID Service Data [5]ParameterValue

2-octet Service UUID followed by additional service data

Public Broadcast
Announcement
Service UUID

2

0x1856

Defined in Bluetooth® Assigned Numbers [5]Public Broadcast
Announcement
features1

0x02

Bit 0 = 0b0 (Not encrypted)
Bit 1 = 0b1 (Standard Quality present)
Bit 2 = 0b0 (High Quality not present)

Table 6.6: Advertising data format for the Public Broadcast Announcement as shown in Figure 6.3.

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