SIST EN 61603-7:2004

SLOVENSKI STANDARD
SIST EN 61603-7:2004
01-oktober-2004
6LVWHPL]DSUHQRVDYGLRR]LURPDYLGHRLQVRURGQLKVLJQDORY]LQIUDUGHþLP
VHYDQMHPGHO'LJLWDOQLDYGLRVLJQDOL]DNRQIHUHQFHLQSRGREQRXSRUDER,(&

Transmission systems for audio and/or video and related signals using infra-red radiation
-- Part 7: Digital audio signals for conference and similar applications
Übertragung von Ton- und/oder Bildsignalen und verwandten Signalen mit Infrarot-
Strahlung -- Teil 7: Digitale Audiosignale für Konferenzsysteme und ähnliche
Anwendungen
Transmission de signaux audio et/ou vidéo et de signaux similaires au moyen du
rayonnement infrarouge -- Partie 7: Systèmes de transmissions numériques des signaux
audio destinés aux conférences et applications similaires
Ta slovenski standard je istoveten z: EN 61603-7:2003
ICS:
33.160.99 Druga avdio, video in Other audio, video and
avdiovizuelna oprema audiovisual equipment
SIST EN 61603-7:2004 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

SIST EN 61603-7:2004

---------------------- Page: 2 ----------------------

SIST EN 61603-7:2004
EUROPEAN STANDARD EN 61603-7
NORME EUROPÉENNE
EUROPÄISCHE NORM October 2003

ICS 33.160.99; 33.040.20 Partly supersedes EN 61603-3:1998


English version


Transmission systems for audio and/or video and related signals
using infra-red radiation
Part 7: Digital audio signals for conference and similar applications
(IEC 61603-7:2003)


Transmission de signaux audio  Übertragung von Ton- und/oder
et/ou vidéo et de signaux similaires Bildsignalen und verwandten Signalen
au moyen du rayonnement infrarouge mit Infrarot-Strahlung
Partie 7: Systèmes de transmissions Teil 7: Übertragungssysteme für digitale
numériques des signaux audio destinés Audiosignale für Konferenzsysteme
aux conférences et applications similaires und ähnliche Anwendungen
(CEI 61603-7:2003) (IEC 61603-7:2003)






This European Standard was approved by CENELEC on 2003-10-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels


© 2003 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61603-7:2003 E

---------------------- Page: 3 ----------------------

SIST EN 61603-7:2004
EN 61603-7:2003 - 2 -
Foreword

The text of document 100/649/FDIS, future edition 1 of IEC 61603-7, prepared by Technical Area 3,
Infrared systems and applications, of IEC TC 100, Audio, video and multimedia systems and equipment,
was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 61603-7 on
2003-10-01.

This European Standard supersedes 2.6.2 of EN 61603-3:1998.

The following dates were fixed:

– latest date by which the EN has to be implemented
 at national level by publication of an identical
 national standard or by endorsement (dop) 2004-07-01

– latest date by which the national standards conflicting
 with the EN have to be withdrawn (dow) 2006-10-01

Annexes designated "normative" are part of the body of the standard.
Annexes designated "informative" are given for information only.
In this standard, annexes A and ZA are normative and annexes B and C are informative.
Annex ZA has been added by CENELEC.
__________

Endorsement notice

The text of the International Standard IEC 61603-7:2003 was approved by CENELEC as a European
Standard without any modification.
__________

---------------------- Page: 4 ----------------------

SIST EN 61603-7:2004
- 3 - EN 61603-7:2003
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any
of these publications apply to this European Standard only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
IEC 61603-1 1997 Transmission of audio and/or video and EN 61603-1 1997
+ corr. May 1997 related signals using infra-red radiation
Part 1: General

IEC 61603-3 1997 Part 3: Transmission systems for audio EN 61603-3 1998
signals for conference and similar
systems

1)
IEC 61920 - Infrared free air applications - -

ISO/IEC 7498-1 1994 Information technology - Open systems EN ISO/IEC 7498-1 1995
interconnection - Basic reference model
Part 1: The basic model




1)
To be published.

---------------------- Page: 5 ----------------------

SIST EN 61603-7:2004

---------------------- Page: 6 ----------------------

SIST EN 61603-7:2004
INTERNATIONAL IEC
STANDARD
61603-7
First edition
2003-05
Transmission systems of audio and/or video and
related signals using infra-red radiation –
Part 7:
Digital audio signals for conference and
similar applications
 IEC 2003  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch  Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale
U
International Electrotechnical Commission
Международная Электротехническая Комиссия
For price, see current catalogue

---------------------- Page: 7 ----------------------

SIST EN 61603-7:2004
– 2 – 61603-7  IEC:2003(E)
CONTENTS
FOREWORD . 4
1 Scope . 5
2 Normative references. 5
3 Terms and definitions . 5
4 Abbreviations. 5
5 Explanation of terms and general information . 6
6 System considerations. 6
7 Basic system concept . 6
8 Protocol . 7
8.1 System context . 7
8.2 Physical layer . 8
8.3 Data link layer .13
8.4 Detailed overview of audio frame structures.15
9 Data protocol .17
9.1 General .17
9.2 Data messages.18
9.3 Data packet structure.21
Annex A (normative) Definition of prototype filter .23
Annex B (informative) Example of λ/f diagram in the user area conference.24
Annex C (informative) Provision for future developments .25
Bibliography.26
Figure 1 – System . 7
Figure 2 – Conceptual model. 7
Figure 3 – Band allocation for 6 modulated sub-carriers. 8
Figure 4 – (D)QPSK constellation and differential decoding algorithm . 9
Figure 5 – Pulse response of a raised cosine channel filter .10
Figure 6 – Scrambler.11
Figure 7 – Block diagram of sub-band APCM encoder.12
Figure 8 – Quantization of sub-band samples.13
Figure 9 – Superframe structure.14
Figure 10 – RS frame structure .14
Figure 11 – Audio block structure.15
Figure 12 – CRC calculation.15
Figure 13 – Audio block structure for medium quality .16
Figure 14 – Bit-pool sample structure for medium quality .16
Figure 15 – Audio block structure for high quality.16
Figure 16 – Bit-pool sample structure for high quality.17
Figure 17 – Positioning of the data protocol .18

---------------------- Page: 8 ----------------------

SIST EN 61603-7:2004
61603-7  IEC:2003(E) – 3 –
Figure 18 – Data message build-up.18
Figure 19 – Configuration message structure .19
Figure 20 – Display message structure for ASCII display data.20
Figure 21 – Display message structure for bitmap display data .21
Figure 22 – Segmentation of data messages.21
Figure 23 – Data packets fitted on to the superframe structure.22
Table 1 – Sub-carrier centre frequencies. 8
Table 2 – Phase transitions of the differential encoding algorithm . 9
Table 3 – Characteristics of sub-band APCM encoder.12
Table 4 – Definition of audio mode bits .15
Table 5 – Audio blocks and audio quality .17
Table 6 – Data message identifier definition.18
Table 7 – SCI definition.19
Table 8 – Channel allocation table .19
Table 9 – Audio quality mode (AQM) to number of audio blocks used.20
Table C.1 – Sub-carrier allocation .25

---------------------- Page: 9 ----------------------

SIST EN 61603-7:2004
– 4 – 61603-7  IEC:2003(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
TRANSMISSION SYSTEMS OF AUDIO AND/OR VIDEO
AND RELATED SIGNALS USING INFRA-RED RADIATION –
Part 7: Digital audio signals for conference and
similar applications
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International
Organization for Standardization (ISO) in accordance with conditions determined by agreement between the
two organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61603-7 has been prepared by Technical Area 3, Infrared systems
and applications, of IEC technical committee 100: Audio, video and multimedia systems and
equipment.
This first edition cancels and replaces 2.6.2 of IEC 61603-3 (1997).
The text of this standard is based on the following documents:
FDIS Report on voting
100/649/FDIS 100/676/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until 2005.
At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.

---------------------- Page: 10 ----------------------

SIST EN 61603-7:2004
61603-7  IEC:2003(E) – 5 –
TRANSMISSION SYSTEMS OF AUDIO AND/OR VIDEO
AND RELATED SIGNALS USING INFRA-RED RADIATION –
Part 7: Digital audio signals for conference and
similar applications
1 Scope
This part of IEC 61603 describes the characteristics of a digital multiple channel, multiple
carrier audio transmission system as an extension to conference interpretation or similar
systems using the frequency ranges 45 kHz to 1 MHz and 2 MHz to 6 MHz.
NOTE These frequency ranges are also covered by analogue pulse systems used for the same applications.
Interference is not expected because both transmission systems are normally not applied at the same time in the
same room.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 61603-1:1997, Transmission of audio and/or video and related signals using infrared
radiation – Part 1: General
IEC 61603-3:1997, Transmission of audio and/or video and related signals using infrared
radiation – Part 3: Transmission systems for audio signals for conference and similar systems
1
IEC 61920, Infrared transmission systems – Free air applications
ISO/IEC 7498-1:1994, Information technology – Open Systems Interconnection – Basic
Reference Model: The Basic Model
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61603-1 apply.
4 Abbreviations
APCM Adaptive pulse code modulation
AQM Audio quality mode
CAT Channel allocation table
CM Configuration message
CRC Cyclic redundancy check
DCI Display changed identifier
DM Display message
DM-CRC Data message CRC
___________
1
 To be published. For the purposes of the reference in C.1, IEC 61920:1998 is equally valid.

---------------------- Page: 11 ----------------------

SIST EN 61603-7:2004
– 6 – 61603-7  IEC:2003(E)
DMI Data message identifier
DML Data message length
DQPSK Differential quadrature phase shift keying
HQ High quality
MAXCN Maximum channel number
MHQ Mono high quality
MMQ Mono medium quality
MQ Medium quality
OSI Open systems interconnection
PCM Pulse code modulation
PRBS Pseudo-random binary sequence
SCI Source coding identifier
SEI Setting changed identifier
SF Scale factor
SHQ Stereo high quality
SMQ Stereo medium quality
SRRC Square root raised cosine
Exclusive OR
XOR
5 Explanation of terms and general information
For the purposes of this part of IEC 61603, the explanation and information given in
IEC 61603-3, Clause 2, apply.
6 System considerations
For the purposes of this part of IEC 61603, the considerations given in IEC 61603-3, Clause
3, apply.
NOTE With regard to the primary band, the special caution advised in IEC 61603-3, 3.3 should be observed,
especially for inductive lighting and future developments.
7 Basic system concept
The basic system concept is shown in Figure 1.
The system consists of a number (N) of audio sources, either analogue or digital, which are
connected to a transmitter. The transmitter processes the audio signals (in accordance with
the protocol described in Clause 8) into an electrical output to feed the infrared radiator. The
infrared signal is received by the infrared receiver that processes the signal and outputs an
audio signal and/or associated data.

---------------------- Page: 12 ----------------------

SIST EN 61603-7:2004
61603-7  IEC:2003(E) – 7 –
N sources
Audio Audio
Audio Audio
source
source source source
Transmitter
Infrared
Infrared
radiator
receiver
IEC  1548/03
Figure 1 – System
8 Protocol
8.1 System context
In terms of the conceptual OSI reference model, the transmission protocol shall implement the
following layers:
User data
Audio streams
(low rate, limited)
Higher OSI protocol Higher OSI protocol
layers layers
Data link layer (layer 2)
IEC 61603-7
IEC 61603-7
Physical layer (layer 1) IEC 61603-1
IEC 61920
Medium
IEC  1549/03
Figure 2 – Conceptual model
Figure 2 shows the system context using the OSI reference model. Layers 1 and 2 will be part
of the transmission protocol defined in this standard.

---------------------- Page: 13 ----------------------

SIST EN 61603-7:2004
– 8 – 61603-7  IEC:2003(E)
8.2 Physical layer
8.2.1 General
OSI layer 1 (physical layer) shall use infrared radiation as the transfer medium between
radiator and receiver as specified in IEC 61920 and IEC 61603-1.
8.2.2 Carrier
λ
Optical wavelength at the optical peak intensity : 875 nm ± 25 nm
P
8.2.3 Sub-carriers
Primary frequency band (band IV): 2 MHz – 6 MHz
Secondary frequency band (band II): 45 kHz – 1 MHz.
NOTE The secondary frequency band, 45 kHz to 1 MHz, is under consideration.
Figure 3 shows the wideband allocation in the primary band, with the frequencies of each sub-
carrier. A guard band between the transmission bands has been included. Table 1 shows the
frequencies of each sub-carrier.
f  MHz
2,333 3 3,667 4,333 5 5,667
Guardband
IEC  1550/03
Figure 3 – Band allocation for 6 modulated sub-carriers
Table 1 – Sub-carrier centre frequencies
Frequency
Sub-carrier
kHz
CC1 2333,333
CC2 3000
CC3 3666,667
CC4 4333,333
CC5 5000
CC6 5666,667
8.2.4 Occupied bandwidth
The occupied bandwidth is defined as follows.
B =r ⋅()1+ β
occ S
where
B is the occupied bandwidth;
occ

---------------------- Page: 14 ----------------------

SIST EN 61603-7:2004
61603-7  IEC:2003(E) – 9 –
r
b
r is the symbol rate ( = for (D)QPSK, r is the bit rate (see 8.3));
b
S
2
β is the roll-off factor (see 8.2.6).
8.2.5 Sub-carrier modulation
The modulation method is (D)QPSK. The constellation is shown in Figure 4a. The differential
decoding algorithm is shown in Figure 4b. The phase transitions for the differential encoding
algorithm are also listed in Table 2.
00 00
Q
10
01 11
01
11
10 11
01 11
01
I 11
11
01
10
00 10
01
00 10
10
00 00
a) b)
IEC  1551/03
Figure 4 – (D)QPSK constellation and differential decoding algorithm
Table 2 – Phase transitions of the differential
encoding algorithm
Phase change Symbol IQ
 0° 00
90° 01
180° 11
–90° 10
8.2.6 Filter characteristics
A channel filter is included. A square root raised cosine (SRRC) characteristic, as illustrated
in Figure 5, is implemented in both the transmitter and the receiver resulting in a total transfer
characteristic of a raised cosine.
The roll-off factor of the filter is β = 0,4.

---------------------- Page: 15 ----------------------

SIST EN 61603-7:2004
– 10 – 61603-7  IEC:2003(E)
1
0,8
0,6
0,4
0,2
0
0Tb 2Tb 3Tb
–0,2
IEC  1552/03
Figure 5 – Pulse response of a raised cosine channel filter
The combined filter characteristic from the transmitting and receiving filter shall be in
accordance with the following equation:
r

b
T f ≤ (1− β )
b

2

r r r
 π  
2
b b b
P ( f ) = T • cos f − (β +1) (1− β ) < f ≤ (1+ β )
 

r b
 
4β 2 2 2
 

r

b
0 f > (1+ β )

 2
where
P ( f ) is the power transfer function;
r
f is the frequency (Hz);
is the bit rate (bit/s);
r
b
1
T =
b
r
b
β is the roll-off factor.
8.2.7 Channel coding
8.2.7.1 Reed-Solomon encoder
A shorted Reed-Solomon encoder (n,k,d) = (28,24,5) on 8-bit symbols is used. The Reed-
8
Solomon encoder operates in Galois Field GF(2 ).
The field generator polynomial is:
8 4 3 2
p()x = x + x + x + x +1

---------------------- Page: 16 ----------------------

SIST EN 61603-7:2004
61603-7  IEC:2003(E) – 11 –
The code generator polynomial is:
3
i
g()x = ()x +α
∏
i = 0
4 75 3 249 2 78 6
= x +α x +α x +α x +α
α = 02(HEX)
8.2.7.2 Scrambler
The scrambler consists of an XOR gate and a pseudo-random binary sequence (PRBS)
generator. The length of the PRBS is 11 bits and is initialized after every frame sync. The
polynomial that is used for the PRBS is
9 11
1 + x + x
and the initial pattern is
Initial pattern = “10010101000”
A diagram of the scrambler is shown in Figure 6. Scrambling is not applied to the frame sync.
Data in
Initial value
PRBS generator
1 0 0 1 0 1 0 1 0 0 0
Load
0 1 2 3 4 5 6 7 8 9 10
Clock
Data out
IEC  1553/03
Figure 6 – Scrambler
8.2.8 Audio source coding
8.2.8.1 General
The linear PCM audio signal (f = 44,1 kHz) is divided into 4 sub-band signals by an
s
(analysis) filter bank. The 4 sub-band signals are decimated by a factor 4 and quantized
by an adaptive pulse code modulation (APCM) coding scheme. A block diagram of the
encoder is shown in Figure 7.

---------------------- Page: 17 ----------------------

SIST EN 61603-7:2004
– 12 – 61603-7  IEC:2003(E)
Linear PCM samples
APCM
4
x(n)
h(0,n)
encode
APCM
4
h(1,n)
encode
Bit
multi-
plexer
APCM
4
h(2,n)
encode
APCM
4
h(3,n)
encode
IEC  1554/03
Figure 7 – Block diagram of sub-band APCM encoder
Two coding qualities are available: medium quality (MQ) and high quality (HQ). The
characteristics are shown in Table 3.
Table 3 – Characteristics of sub-band APCM encoder
Parameter MQ HQ
Audio bandwidth (kHz) 10 20
Number of used sub-bands 2 4
Bit-pool 11 22
Output bit-rate (kbit/s) 136 272
8.2.8.2 Filter banks
The analysis filters are represented by h(k,n). These filters are derived from a prototype filter
p(n) with length L = 40 (see Annex A). With k the number of the sub-band, k∈(0,3) and n the
index of the prototype filter n∈(0,L-1) the following is given:
h()k,n = c(k,n)× p(n)
a
with
 
π  1
c = cos ×()n − 2 × k + 
 
a
 
4 2
 
 
8.2.8.3 Sub-band APCM coding
The decimator output samples are saved in buffers. Each 24-sample period (544 μs),
4 blocks of 6 sub-band samples are filled and available for APCM coding.
The sub-band APCM coding operates on 16 bit samples and performs the steps listed below.
NOTE At the output of the decimators all samples have to be quantized to 16 bits.
The value k specifies the index of the sub-band, k∈(0,3) for HQ and k∈(0,1) for MQ coding.
The value n specifies the number of coded sub-bands, 4 for HQ and 2 for MQ coding.
bands
a) The largest absolute value in each block is searched for: M(k).
b) From the value of M(k), the scale factor (SF) F (k) is calculated:
scale
2
F ()k = log()M()k
 
scale

---------------------- Page: 18 ----------------------

SIST EN 61603-7:2004
61603-7  IEC:2003(E) – 13 –
c) From the SF values, the number of bits per sub-band is calculated: n ()k ← F (k)
bits scale
− n ()k = max()F (k) − W,0
bits scale
 
F ()k − B
scale
∑
 
∀k
with W =
 
n
 bands 
 
 
where B = bit-pool (see Table 3)
− while n ()k < B → increment n (k) by 1, starting with k = 0 and increasing k
bits
∑ bits
∀k
until n ()k = B
∑ bits
∀k
while n ()k > B → decrement n (k) by 1, starting with k = 3 (HQ) or k = 1
bits
∑ bits
∀k
(MQ) and decreasing k until n ()k = B
∑ bits
∀k
d) quantize all samples in the block of sub-band k to n (k) bits (see example of 7-bit
bits
quantization in Figure 8)
bit position 15 SF+1 0
16-bit sample
bits(k) = 7
7-bit quantized sample
IEC  1555/03
Figure 8 – Quantization of sub-band samples
The output of the sub-band APCM coder consists of all quantized sub-band samples together
with the scale factors.
8.3 Data link layer
8.3.1 General
The major building block of the data link layer protocol is a superframe (see Figure 9).

---------------------- Page: 19 ----------------------

SIST EN 61603-7:2004
– 14 – 61603-7  IEC:2003(E)
Audio
Sub-band samples Scale factors CRC
mode
(66 bits) (5 bits)
(8 bits)
(1 bit)
1 audio block (10 bytes)
Audio block A Audio block B DATA RS parity
(10 bytes) (10 bytes) (4 bytes) (4 bytes)
1 RS frame (28 bytes)
SYNC RS frame 0 RS frame 1 RS frame 2 RS frame 3 RS frame 4 RS frame 5
(3 bytes) (28 bytes) (28 bytes) (28 bytes) (28 bytes) (28 bytes) (28 bytes)
1 superframe (1 368 bits) ; 1,632 ms
IEC  1556/03
Figure 9 – Superframe structure
A superframe consists of a SYNC pattern followed by 6 RS frames. This results in a size of
1 368 bits per superframe. With a bit-rate of 837,9 kbit/s, the total length of a superframe is
1,632 ms. This is exactly 3 times the length of an APCM frame (at the input of an encoder).
8.3.2 Synchronization information
Before 6 consecutive RS frames a SYNC word is transmitted. The SYNC word equals the
hexadecimal value D21DB8.
8.3.3 Error coding redundancy
A Reed-Solomon encoder is applied to protect the audio and data information from
transmission errors. The Reed-Solomon encoder adds 4 bytes of redundant information, to
8
each pair of audio blocks in combination with 1 data slot. An RS(28,24) in GF(2 ) has been
chosen (see 8.2.7). The structure of an RS frame is shown in Figure 10.
Audio block A Audio block B DATA RS parity
(10 bytes) (10 bytes) (4 bytes) (4 bytes)
1 RS frame (28 bytes)
IEC  1557/03
Figure 10 – RS fr
...