ETSI TS 103 466 V1.2.1 (2019-09)

TECHNICAL SPECIFICATION
Digital Audio Broadcasting (DAB);
DAB audio coding (MPEG Layer II)

2 ETSI TS 103 466 V1.2.1 (2019-09)

Reference
RTS/JTC-DAB-96
Keywords
audio, broadcasting, coding, DAB, digital
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3 ETSI TS 103 466 V1.2.1 (2019-09)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definition of terms, abbreviations, mathematical symbols and convention . 7
3.1 Terms . 7
3.2 Abbreviations . 9
3.3 Mathematical symbols . 10
3.3.1 Arithmetic operators . 10
3.3.2 Logical and set operators . 10
3.3.3 Functions . 10
3.3.4 Constants . 10
3.4 C-language mathematical symbols . 11
3.4.1 Arithmetic operators . 11
3.4.2 Logical operators . 11
3.4.3 Relational operators . 11
3.4.4 Assignment . 11
3.4.5 Mnemonics . 11
3.4.6 Method of describing bit stream syntax . 12
3.5 Convention . 13
4 Introduction . 13
5 DAB audio coding . 13
5.1 Introduction . 13
5.2 Audio encoding . 14
5.2.0 General . 14
5.2.1 Analysis sub-band filter . 15
5.2.2 Scale Factor calculation . 17
5.2.3 Coding of Scale Factors . 17
5.2.4 Coding of Scale Factor Selection Information . 18
5.2.5 Psychoacoustic model . 19
5.2.6 Bit allocation . 19
5.2.7 Bit allocation coding . 20
5.2.8 Quantization and coding of sub-band samples. 22
5.2.9 Formatting of the audio bit stream . 24
5.3 Semantics of the audio bit stream . 25
5.3.1 MPEG Audio Layer II bit stream . 25
5.3.1.1 Audio sequence . 25
5.3.1.2 Audio frame . 25
5.3.1.3 Audio frame header . 25
5.3.1.4 Error check . 28
5.3.1.5 Audio data . 28
5.3.1.6 Ancillary data . 29
5.3.2 DAB audio bit stream . 29
5.3.2.0 Introduction . 29
5.3.2.1 DAB audio sequence . 29
5.3.2.2 DAB audio frame . 29
5.3.2.3 DAB audio frame header . 30
5.3.2.4 Error check . 30
5.3.2.5 Audio data . 30
5.3.2.6 Audio stuffing bits . 30
5.3.2.7 Extended Programme Associated Data (X-PAD) . 30
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4 ETSI TS 103 466 V1.2.1 (2019-09)
5.3.2.8 Scale Factor Error Check (ScF-CRC) . 31
5.3.2.9 Fixed Programme Associated Data (F-PAD) . 31
5.4 Audio bit stream syntax . 33
5.4.0 Introduction. 33
5.4.1 ISO/IEC 11172-3 and ISO/IEC 13818-3 Layer II bit stream syntax . 33
5.4.1.0 General . 33
5.4.1.1 Audio sequence . 33
5.4.1.2 Audio frame . 33
7.3.1.3 Header . 33
5.4.1.4 Error check . 34
5.4.1.5 Audio data . 34
5.4.1.6 Ancillary data . 35
5.4.2 DAB audio bit stream syntax . 35
5.4.2.0 General . 35
5.4.2.1 DAB audio sequence . 35
5.4.2.2 DAB audio frame . 35
5.4.2.3 DAB audio frame header . 35
5.4.2.4 Error check . 35
5.4.2.5 Audio data . 35
5.4.2.6 Audio stuffing bits . 36
5.4.2.7 Extended Programme Associated Data . 36
5.4.2.8 Scale factor error check . 36
5.4.2.9 Fixed Programme Associated Data . 36
5.5 Programme Associated Data (PAD) . 37
5.5.1 Coding . 37
5.5.2 Transport . 37
5.5.3 Dynamic Range Control data . 38
Annex A (informative): Main characteristics of the audio coding system . 39
A.1 Audio signal characteristics . 39
A.2 Audio coding characteristics . 39
A.3 Audio associated data characteristics . 40
Annex B (normative): Audio decoding . 41
B.1 General . 41
B.2 CRC check for audio side information . 41
B.3 CRC check for Scale Factors . 41
B.4 Decoding of the MPEG Audio Layer II bit stream . 42
Annex C (informative): Audio encoding . 43
C.1 Analysis sub-band filter. 43
C.2 Psychoacoustic model . 46
C.3 Bit allocation procedure . 54
C.4 Bit sensitivity to errors . 56
C.5 Error concealment . 57
C.6 Joint stereo coding . 57
History . 60

ETSI
5 ETSI TS 103 466 V1.2.1 (2019-09)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This Technical Specification (TS) has been produced by Joint Technical Committee (JTC) Broadcast of the European
Broadcasting Union (EBU), Comité Européen de Normalisation ELECtrotechnique (CENELEC) and the European
Telecommunications Standards Institute (ETSI).
NOTE 1: The EBU/ETSI JTC Broadcast was established in 1990 to co-ordinate the drafting of standards in the
specific field of broadcasting and related fields. Since 1995 the JTC Broadcast became a tripartite body
by including in the Memorandum of Understanding also CENELEC, which is responsible for the
standardization of radio and television receivers. The EBU is a professional association of broadcasting
organizations whose work includes the co-ordination of its members' activities in the technical, legal,
programme-making and programme-exchange domains. The EBU has active members in about
60 countries in the European broadcasting area; its headquarters is in Geneva.
European Broadcasting Union
CH-1218 GRAND SACONNEX (Geneva)
Switzerland
Tel: +41 22 717 21 11
Fax: +41 22 717 24 81
The Eureka Project 147 was established in 1987, with funding from the European Commission, to develop a system for
the broadcasting of audio and data to fixed, portable or mobile receivers. Their work resulted in the publication of
European Standard, ETSI EN 300 401 [1], for DAB (see note 2) which now has worldwide acceptance.
NOTE 2: DAB is a registered trademark owned by one of the Eureka Project 147 partners.
The DAB family of standards is supported by WorldDAB, an organization with members drawn from broadcasting
organizations and telecommunication providers together with companies from the professional and consumer
electronics industry.
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
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6 ETSI TS 103 466 V1.2.1 (2019-09)
1 Scope
The present document defines the method to code and transmit audio services using the MPEG Layer II audio coder for
Digital Audio Broadcasting (DAB) (ETSI EN 300 401 [1]) and details the necessary mandatory requirements for
decoders. The permitted audio modes and the data protection and encapsulation are detailed. This audio coding scheme
permits the full use of the PAD channel for carrying dynamic labels and user applications.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference/.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] ETSI EN 300 401 (V2.1.1): "Radio Broadcasting Systems; Digital Audio Broadcasting (DAB) to
mobile, portable and fixed receivers".
[2] ISO/IEC 11172-3 (1993): "Information technology - Coding of moving pictures and associated
audio for digital storage media at up to 1,5 Mbit/s - Part 3: Audio".
[3] IEC 60958 (all parts): "Digital audio interface".
[4] ISO/IEC 13818-3: "Information technology - Generic coding of moving pictures and associated
audio information - Part 3: Audio".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
Not applicable.
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7 ETSI TS 103 466 V1.2.1 (2019-09)
3 Definition of terms, abbreviations, mathematical
symbols and convention
3.1 Terms
For the purposes of the present document, the terms given in ETSI EN 300 401 [1] and the following apply:
alias component: mirrored signal component resulting from sub-Nyquist sampling
audio bit stream: sequence of consecutive audio frames
audio frame: frame of a duration of 24 ms (at 48 kHz sampling frequency) or of 48 ms (at 24 kHz sampling frequency)
which contains a Layer II encoded audio signal ISO/IEC 11172-3 [2], ISO/IEC 13818-3 [4], corresponding to
1 152 consecutive audio samples
NOTE: It is the smallest part of the audio bit stream which is decodable on its own.
audio mode: audio coding system provides single channel, stereo and joint stereo audio modes
NOTE: In each mode, the complete audio signal is encoded as one audio bit stream.
bark: unit of the critical band
NOTE: The Bark scale is a non-linear mapping of the frequency scale over the entire audio frequency range.
bit allocation: time-varying assignment of bits to samples in different sub-bands according to a psychoacoustic model
bound: lowest sub-band in which Intensity stereo coding is used, in the case of joint stereo mode
Common Interleaved Frame (CIF): serial digital output from the main service multiplexer which is contained in the
Main Service Channel part of the transmission frame
NOTE: It is common to all transmission modes and contains 55 296 bits (i.e. 864 CUs).
convolutional coding: coding procedure which generates redundancy in the transmitted data stream in order to provide
ruggedness against transmission distortions
critical band: psychoacoustic measure in the frequency domain which corresponds to the frequency selectivity of the
human ear
DAB audio frame: Same as audio frame, but includes all specific DAB audio-related information.
dual channel mode: audio mode, in which two audio channels with independent programme contents are encoded
within one audio bit stream
NOTE: This audio mode is not used in DAB.
Equal Error Protection (EEP): error protection procedure which ensures a constant protection of the bit stream
Extended Programme Associated Data (X-PAD): extended part of the PAD carried towards the end of the DAB
audio frame, immediately before the Scale Factor Cyclic Redundancy Check (CRC)
NOTE: Its length is variable.
Fixed Programme Associated Data (F-PAD): fixed part of the PAD contained in the last two bytes of the DAB audio
frame
intensity stereo coding: method of exploiting stereo irrelevance or redundancy in stereophonic audio programmes
NOTE: It is based on retaining only the energy envelope of the right and left channels at high frequencies. At low
frequencies, the fine structure of the left and right channel of a stereophonic signal is retained.
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8 ETSI TS 103 466 V1.2.1 (2019-09)
joint stereo mode: audio mode, in which two channels forming a stereo pair (left and right) are encoded within one bit
stream and for which stereophonic irrelevance or redundancy is exploited for further bit reduction
NOTE: The method used in the DAB system is Intensity stereo coding.
logical frame: data burst, contributing to the contents of a sub-channel, during a time interval of 24 ms
EXAMPLE: Data bursts at the output of an audio encoder, a Conditional Access scrambler and a convolutional
encoder are referred to as logical frames. The number of bits contained in a specific logical frame
depends on the stage in the encoding process and the bit rate associated with the sub-channel.
Main Service Channel (MSC): channel which occupies the major part of the transmission frame and which carries all
the digital audio service components, together with possible supporting and additional data service components
masking: property of the human auditory system by which an audio signal cannot be perceived in the presence of
another audio signal
masking threshold: function of frequency and time, specifying the sound pressure level below which an audio signal
cannot be perceived by the human auditory system
N: length of Fast Fourier Transform (FFT)
polyphase filter bank: set of equal-bandwidth filters with special phase relationship, allowing for efficient
implementation of a filter bank
Programme Associated Data (PAD): information which is related to the audio data in terms of contents and
synchronization
NOTE: The PAD field is located at the end of the DAB audio frame.
protection level: level specifying the degree of protection, provided by the convolutional coding, against transmission
errors
protection profile: scheme of convolutional coding applied
psychoacoustic model: mathematical model of the masking behaviour of the human auditory system
Scale Factor (ScF): factor by which a set of values is scaled before quantization
NOTE: The numerical code for the Scale Factor is called the Scale Factor Index.
Scale Factor Select Information (ScFSI): 2-bit code which indicates for each sub-band how many Scale Factors are
coded within the audio frame
service: user-selectable output which can be either a programme service or a data service
service component: part of a service which carries either audio (including PAD) or data
NOTE: The service components of a given service are linked together by the Multiplex Configuration
Information. Each service component is carried either in a sub-channel or in the Fast Information Data
Channel.
side information: information in the encoded audio bit stream which is necessary for controlling the audio decoder
NOTE: This information includes Bit Allocation, Scale Factor Select Information and Scale Factors.
single channel mode: audio mode, in which a monophonic audio programme is encoded within one bit stream
stereo mode: audio mode, in which two channels forming a stereo pair (left and right) are encoded within one bit
stream
stuffing: one or more bits which may be inserted into the audio bit stream
NOTE: Stuffing bits are ignored by the audio decoding process. The purpose is to fill up a data field when
required.
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9 ETSI TS 103 466 V1.2.1 (2019-09)
sub-band: subdivision of the audio frequency range
NOTE: In the audio coding system, 32 sub-bands of equal bandwidth are used.
sub-band samples: sub-band filter bank in the audio encoder creates a filtered and sub-sampled representation of the
input audio signal
NOTE: The filtered samples are called sub-band samples. From 384 consecutive input audio samples, 12
consecutive sub-band samples are generated for each of the 32 sub-bands.
syncword: 12-bit code embedded in the MPEG Audio Layer II bit stream ISO/IEC 11172-3 [2], ISO/IEC 13818-3 [4]
that identifies the beginning of an audio frame
Unequal Error Protection (UEP): error protection procedure which allows the bit error characteristics to be matched
with the bit error sensitivity of the different parts of the bit stream
X-PAD data group: package of data used for one user application in the Extended Programme Associated
Data (X-PAD)
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in ETSI EN 300 401 [1] and the following apply:
AES Audio Engineering Society
ASCTy Audio Service Component Type
CIF Common Interleaved Frame
CRC Cyclic Redundancy Check
DAB Digital Audio Broadcasting
DRC Dynamic Range Control
EBU European Broadcasting Union
EEP Equal Error Protection
FFT Fast Fourier Transform
F-PAD Fixed Programme Associated Data
ID Identifier of audio coding algorithm
ISO International Organization for Standardization
LSb Least Significant bit
LSF Lower Sampling Frequency
M/S Music/Speech
MPEG Moving Pictures Expert Group
MSb Most Significant bit
MSB Most Significant Byte
PAD Programme Associated Data
PCM Pulse Coded Modulation
ScF Scale Factor
ScF-CRC audio Scale Factor - Cyclic Redundancy Check (error check)
ScFSI Scale Factor Select Information
SMR Signal-to-Mask Ratio
SPL Sound Pressure Level
UEP Unequal Error Protection
X-PAD eXtended Programme Associated Data
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10 ETSI TS 103 466 V1.2.1 (2019-09)
3.3 Mathematical symbols
3.3.1 Arithmetic operators
For the purposes of the present document, the following mathematical symbols apply:
^ Power
/ Integer division with truncation of the result toward zero;
for example, 7/4 and -7/-4 are truncated to 1 and -7/4 and 7/-4 are truncated to -1
Q(a/b) Q(a/b) is the quotient part of the division of a by b (a and b positive integers)
R(a/b) R(a/b) is the remainder of the division of a by b
 R (a / b) if a is a positive integer
mod(a,b) (b positive integer)
mod( a,b) =

R((b - R(-a/b))/b ) if a is a negative integer

(mod p) Modulo p operation
3.3.2 Logical and set operators
For the purposes of the present document, the following mathematical symbols apply:
max [,.,] The maximum value in the argument list
min [,.,] The minimum value in the argument list
⊕ Exclusive or
∩ Set intersection
Set union
∪
\ Set exclusion: {-3, -2, ., 3} \ {0} is the set of integers {-3, -2, -1, 1, 2, 3}
3.3.3 Functions
For the purposes of the present document, the following mathematical symbols apply:
sin Sine
cos Cosine
exp Exponential
(.)
e Exponential function
Square root
log10 Logarithm to base 10
j Imaginary unit, j = -1
≤ <
1 if 0 x 1
Rect
Rect (x) =

0 elsewhere

1 if i = j

δ Kronecker symbol
δ(i, j) =

0 if i ≠ j

3.3.4 Constants
For the purposes of the present document, the following mathematical symbols apply:
π 3,14159265359.
e 2,71828182846.
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11 ETSI TS 103 466 V1.2.1 (2019-09)
3.4 C-language mathematical symbols
3.4.1 Arithmetic operators
For the purposes of the present document, the following C-language mathematical symbols apply:
+ Addition
- Subtraction (as a binary operator) or negation (as a unary operator)
++ Increment
- - Decrement
* Multiplication
DIV Integer division with truncation of the result toward -∞
% Modulo operator. Defined only for positive numbers
log Logarithm to base 10
3.4.2 Logical operators
For the purposes of the present document, the following C-language mathematical symbols apply:
|| Logical OR
3.4.3 Relational operators
For the purposes of the present document, the following C-language mathematical symbols apply:
> Greater than
≥ Greater than or equal to
< Less than
≤ Less than or equal to
== Equal to
!= Not equal to
3.4.4 Assignment
For the purposes of the present document, the following C-language mathematical symbols apply:
= Assignment operator
3.4.5 Mnemonics
The following mnemonics are defined to describe the different data types used in the coded DAB audio bit-stream:
bslbf Bit string, left bit first, where "left" is the order in which bit strings are written in the present
document. Bit strings are written as a string of 1 s and 0 s within single quote marks,
e.g. "1000 0001". Blanks within a bit string are for ease of reading and have no significance
bound Number of first sub-band in joint stereo mode
ch Channel. If ch has the value 0 the left channel of a stereo signal or the first of two independent
audio signals is indicated
chlimit Number of channels
dscf Difference between two Scale Factors
gr Granule of three sub-band samples per sub-band
nbal Number of allocated bits per sub-band sample
nch Number of channels; equal to 1 for single channel mode, 2 in other modes
rpchof Remainder polynomial coefficients, highest order first
sb Sub-band
sblimit The number of the lowest sub-band for which no bits are allocated
scfsi Scale Factor selection information
uimsbf Unsigned integer, most significant bit first
The byte order of multi-byte words is most significant byte first.
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12 ETSI TS 103 466 V1.2.1 (2019-09)
3.4.6 Method of describing bit stream syntax
The bit stream described in clause 5 is the bit stream that exists in the DAB-receiver at the interface between channel
decoder and audio decoder. The bit stream is described using the "C" software language which is used to program the
processor which assembles the programme audio and associated data for channel coding. Each data item in the bit
stream is in bold type. It is described by its name, its length in bits, and a mnemonic for its type and order of
transmission.
The action caused by a decoded data element in a bit stream depends on the value of that data element and on data
elements previously decoded. The decoding of the data elements and definition of the state variables used in their
decoding are described in annex B. The following constructs are used to express the conditions when data elements are
present, and are in normal type.
NOTE 1: This syntax uses the "C"-code convention that a variable or expression evaluating to a non-zero value is
equivalent to a condition that is true.
while ( condition ) { If the condition is true, then the group of data elements occurs next
data_element in the data stream. This repeats until the condition is not true.
. . .
}
do {
data_element The data element always occurs at least once.
. . .
} while ( condition ) The data element is repeated until the condition is not true.
if ( condition) { If the condition is true, then the first group of data elements occurs next
data_element in the data stream.
. . .
}
else { If the condition is not true, then the second group of data elements
data_element occurs next in the data stream.
. . .
}
for (expr1; expr2; expr3) { expr1 is an expression specifying the initialization of the loop.
data_element Normally it specifies the initial state of the counter. expr2 is a condition specifying a
test made before each iteration of the loop.
. . . The loop terminates when the condition is not true.
} expr3 is an expression that is performed at the end of each iteration of the loop,
normally it increments a counter.

NOTE 2: The most common usage of this construct is as follows.
for ( i = 0; i < n; i++) { The group of data elements occurs n times.
Conditional constructs within the group of data
data_element elements may depend on the value of the loop
. . . control variable i, which is set to zero for the first
occurrence, incremented to one for the second occurrence, and
} so forth.
As noted, the group of data elements may contain nested conditional constructs. For compactness, the {} may be
omitted when only one data element follows.
data_element [] data_element [] is an array of data. The number of data elements is indicated by the
context.
data_element [n] data_element [n] is the (n+1)th element of an array of data.
data_element [m][n] data_element [m][n] is the (m+1),(n+1)th element of a two-dimensional array of data.
data_element [l][m][n] data_element [l][m][n] is the (l+1),(m+1),(n+1)th element of a three-dimensional array
of data.
data_element [m.n] is the inclusive range of bits between bit m and bit n in the data_element.
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13 ETSI TS 103 466 V1.2.1 (2019-09)
3.5 Convention
Unless otherwise stated, the following notation, regarding the order of bits within each step of processing is used:
• in figures, the bit shown in the left hand position is considered to be first;
• in tables, the bit shown in the left hand position is considered to be first;
• in byte fields, the Most Significant bit (MSb) is considered to be first and denoted by the higher number. For
example, the MSb of a single byte is denoted "b " and the Least Significant bit (LSb) is denoted "b ";
7 0
• in vectors (mathematical expressions), the bit with the lowest index is considered to be first.
NOTE: Due to time-interleaving, this order of bits is not the true transmission order.
4 Introduction
The DAB system standard [1] allows audio (programme) services to be carried using either DAB audio or DAB+ audio.
The present document defines the way that audio (programme) services are carried when using DAB audio (MPEG
layer II audio coding).
Two sampling rates are permitted for DAB audio coding, 48 kHz and 24 kHz. Each audio frame contains samples for
24 ms or 48 ms, respectively, and each frame has a constant size. The audio frames are carried in one or two DAB
logical frames, respectively. A range of bit rates and audio modes are available and the addition of Programme
Associated Data (PAD) allows supplementary content to be provided.
5 DAB audio coding
5.1 Introduction
An overview of the principal functions of the audio coding scheme is shown in the simplified block diagram of the
DAB audio encoder (see figure 1). The main characteristics of the audio coding system, like audio modes, bit rates and
audio frame length are given in clause A.2, whereas the characteristics of the input audio signal are given in clause A.1.
sub-band
samples
PCM
audio samples
DAB
48 kHz or 24 kHz audio frame
quantizer
filter bank
frame
and
32 sub-bands
packing
coding
MPEG Audio
psycho- Layer II encoder
bit
[3, 14]
acoustic
allocation
model
PAD
Figure 1: Simplified block diagram of the DAB audio encoder
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14 ETSI TS 103 466 V1.2.1 (2019-09)
The input PCM audio samples are fed into the audio encoder. A filter bank creates a filtered and sub-sampled
representation of the input audio signal. The filtered samples are called sub-band samples. A psychoacoustic model of
the human ear should create a set of data to control the quantizer and coding. These data can be different depending on
the actual implementation of the encoder. An estimation of the masking threshold can be used to obtain these quantizer
control data. The quantizer and coding block shall create a set of coding symbols from the sub-band samples. The frame
packing block shall assemble the actual audio bit stream from the output data of the previous block, and shall add other
information, such as header information, CRC words for error detection and Programme Associated Data (PAD), which
are intimately related with the coded audio signal. For a sampling frequency of 48 kHz, the resulting audio frame
corresponds to 24 ms duration of audio and shall comply with the Layer II format, ISO/IEC 11172-3 [2]. The audio
frame shall map on to the logical frame structure in such a way that the first bit of the DAB audio frame corresponds to
the first bit of a logical frame. For a sampling frequency of 24 kHz, the resulting audio frame corresponds to 48 ms
duration of audio and shall comply with the Layer II LSF format, ISO/IEC 13818-3 [4]. The audio frame shall map on
to the logical frame structure in such a way that the first bit of the DAB audio frame corresponds to the first bit of a
logical frame (this may be associated with either an "even" or an "odd" logical frame count). The formatting of the
DAB audio frame shall be done in such a way that the structure of the DAB audio frame conforms to the audio bit
stream syntax described in clause 5.4.
The simplified block diagram of the audio decoder in the receiver, shown in figure 2, accepts the DAB audio frame in
the syntax defined in clause 5.4.2 which is a conformant subset of the MPEG Audio Layer II (ISO/IEC 11172-3 [2] and
ISO/IEC 13818-3 [4]) bit stream syntax defined in clause 5.4.1. This allows the use of an MPEG Audio Layer II
(ISO/IEC 11172-3 [2] and ISO/IEC 13818-3 [4]) decoder. The DAB audio frame shall be fed into the audio decoder,
which unpacks the data of the frame to recover the various elements of information. The reconstruction block shall
reconstruct the quantized sub-band samples. An inverse filter bank shall transform the sub-band samples back to
produce digital PCM audio signals in the case of ISO/IEC 11172-3 [2] at 48 kHz sampling frequency and in the case of
ISO/IEC 13818-3 [4] at 24 kHz according to annex B.
sub-band
samples
PCM
audio samples
DAB
48 kHz or 24 kHz
audio frame inverse
frame
filter bank
reconstruction
unpacking
32 sub-bands
MPEG Audio Layer II
decoder [3, 14]
PAD
Figure 2: Simplified block diagram of the DAB audio decoder
5.2 Audio encoding
5.2.0 General
The source encoder for the DAB system is the MPEG Audio Layer II (ISO/IEC 11172-3 [2] and ISO/IEC 13818-3 [4])
encoder with restrictions on some parameters and some additional protection against transmission errors. In the
ISO/IEC 11172-3 [2] and ISO/IEC 13818-3 [4] International Standards only the encoded audio bit stream, rather than
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