I
NTERNAT
I
O
NA
L
S
TA N DA
R
D
ISOIIEC
I1
172-3
First
edition
1993-08-01
Information technology
-
Coding
of
moving pictures and associated audio for
digital storage media at
up
to about
1,5
Mbit/s
-
Part
3:
Audio
Technologies de l'information
-
Codage de l'image animee et du son
associe
pour
les
supports
de stockage numerique jusqu'd environ
1,5
MbiVs
-
Partie
3:
Audio
Reference number
ISO/IEC
11
172-3:1993(E)
Licensed to INTEL CORPORATION/LINDA HODGE
ISO Store order #: 539739/Downloaded: 2003-04-11
Single user licence only, copying and networking prohibited
ISOAEC
11 172-3: 1993
(E)
Contents
Page
III
troduc tion..
...................................................
.....................................
v
Section 1: General
..........................................
............................
1
.........................
1.1
Scope
.............................................
1
1.2 Normative references.
.......
......................................................
1
Section 2: Techiiical elements..
....
................................................................
2
2.1 Defiiiitioiis
.......................................
.....................................
2
2.2
Symbols
and
abbreviations..
.................
...........................................
10
2.3 Method of describing bitstream syntax
12
2.4
R
eq
U
ire inen ts
.
.
..............................................................................
14
A
II
II
ex
es
A
Diagrams
......
....
..........................
.......
38
B
Tables
...............
.................
C The encodiug process
.......
.............
D
Psychoacoustic models
....................................................................
..IO9
E
Bit sensitivity to errors.....
............................................................
140
OISO/IEC 1993
All
rights reserved. No part
of
this publicatiori inay be reproduced
or
utilized
in
any form
or
by
any
~neaiis, electronic
or
nech ha ni cal,
i~icluding photocopying
and
microfilm, without
permission
in
writiiig from the publisher.
ISOAEC Copyright Office
Case Postale
56
CH
121
1
Genève
20
Switzerland
Printed in Switzerland.
ii
Licensed to INTEL CORPORATION/LINDA HODGE
ISO Store order #: 539739/Downloaded: 2003-04-11
Single user licence only, copying and networking prohibited
O
ISO/IEC
ISO/IEC
11
172-3:
1993
(E)
F
Error
concealment 142
G
Joint stereo coding 143
H
List
of
patent
holders
.........................................................................
147
.............................................................................
...........................................................................
iii
Licensed to INTEL CORPORATION/LINDA HODGE
ISO Store order #: 539739/Downloaded: 2003-04-11
Single user licence only, copying and networking prohibited
ISO/IEC
11
172-3: 1993
(E)
8
ISO/IEC
Foreword
IS0
(the International Organization for Standardization) and IEC (the Inter-
national Electrotechnical Commission) form the specialized system for
worldwide standardization. National bodies that are members
of
IS0
or
IEC participate in the development of International Standards through
technical committees established by the respective organization to deal
with particular fields of technical activity.
IS0
and IEC technical com-
mittees collaborate in fields of mutual interest. Other international organ-
izations, governmental and non-governmental, in liaison with
IS0
and IEC,
also take part in the work.
In the field of information technology,
IS0
and IEC have established
a
joint
technical committee, ISO/IEC JTC 1. Draft International Standards adopted
by the joint technical committee are circulated to national bodies for vot-
ing. Publication as an International Standard requires approval by
at
least
75
YO
of
the national bodies casting
a
vote.
International Standard iSO/IEC 11 172-3 was prepared by Joint Technical
Committee ISO/IEC JTC 1,
lnformation technology,
Sub-committee
SC
29,
Coded representation
of
audio, picture, multimedia and hypermedia infor-
mation.
ISO/lEC
11
172 consists of the following parts, under the general title
In-
formation technology
-
Coding of moving pictures and associated audio
for digital storage media at up to about
1,5
MbiVs:
-
Part
1:
Systems
-
Part2: Video
-
Part
3:
Audio
-
Part
4:
Compliance testing
Annexes A and
B
form an integral part of this part of ISO/IEC 11 172. An-
nexes
C,
D, E,
F,
G
and
H
are for information only.
iv
Licensed to INTEL CORPORATION/LINDA HODGE
ISO Store order #: 539739/Downloaded: 2003-04-11
Single user licence only, copying and networking prohibited
O
ISO/IEC
t
ISO/IEC
11
172-3: 1993 (E)
model
Introduction
Note:
Readers interested in
an
overview
of
MPEG
Audio should read this Introduction and then proceed to
annex
A
(Diagrams) (and annex
C
(The encoding process) before reading the normative clauses
1
and
2.
To
aid in the understanding of the specification of the stored compressed bitstream and its decoding, a
sequence of encoding, storage and decoding is described.
0.1
Encoding
The encoder processes the digital audio signal and produces the compressed bitstream for storage. The
encoder algorithm is not standardized, and may use various means for encoding such
as
estimation of the
auditory masking threshold, qu(mtization, and scaling. However, the encoder
output
must
be
such
that
a
decoder conforming
to
the
specifications
of
clause
2.4
will produce audio suitable for the intended
application.
PCM
audio samples
32
44,l
48kHz
1
encoded
bitstream
.I,:--
f
ra
quanrizer
4
and
4
pacnllly
I
4
psychoacoustic
ancillary data
ISOAEC
11172-3
encoder
I
Figure
1
--
Sketch
of
the basic structure
of
an encoder
Figure
1
illustrates the basic structure of
a
audio encoder. Input audio samples
are
fed
into the encoder. The
mapping creates
a
filtered and subsampled represenwion of the input audio stream. The mapped samples
may
be
Galled either subb<md samples
(as
in Layer I
or
II, see below)
or
transformed subband samples
(as
in
Layer
ID).
A
psychoacoustic model creates
a
set of
data
to control the quantizer and coding. These
data
are
different depending
on
the actual coder implemenWion. One possibility is to use an estimation of the
masking threshold to do this quantizer control. The quantizer and coding block creates
a
set of coding
symbols
from the mapped input samples. Again, this block can depend on the encoding system. The block
'frame packing' assembles the actual bitstream from the output
&zta
of the other blocks, and adds other
information (e.g. error correction) if necessary.
There
are
four different modes possible, single chmnel, dual channel (two independent audio signals coded
within one bitstrean), stereo (left and right signals of
a
stereo
pair
coded within one bitstream), and Joint
Stereo (left and right signals
of
a
stereo pair coded within one bitstrean with the stereo irrelevancy and
redundancy exploited).
V
Licensed to INTEL CORPORATION/LINDA HODGE
ISO Store order #: 539739/Downloaded: 2003-04-11
Single user licence only, copying and networking prohibited
