IEC 61603-7:2003 pdf – 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 IEC 61920, Infrared transmission systems – Free air applications 1 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
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 each pair of audio blocks in combination with 1 data slot. An RS(28,24) in GF(2 8 ) has been chosen (see 8.2.7). The structure of an RS frame is shown in Figure 10.
8.3.5 Data slots The data slots carry control, configuration, display, … information. This information is sent as messages in a consecutive sequence of data slots. Each data slot is 4 bytes. NOTE The data protocol is described in Clause 9. 8.4 Detailed overview of audio frame structures 8.4.1 Audio mode Each pair of audio blocks (slot A and slot B) contains 2 audio mode bits. These bits indicate the audio mode carried by slot A and slot B (as indicated in Table 4). Bit1 is located in audio block A and bit0 is located in audio block B (see also 8.4.3).
e) Spare field (SPARE) (40-bit) The configuration message can be transmitted in 2 data packets (see 9.3). To fit exactly in the packet payload, the message is extended with a spare field containing zeros. 18.104.22.168 Display message (DM) 22.214.171.124.1 General The purpose of this message is to transmit data for the receiver’s display, such as channel numbers or language names. There are two types of display messages: ASCII for textual displays and bitmap data for graphical displays. 126.96.36.199.2 ASCII display message The ASCII display message consists of a logical channel number, a display changed identifier DCI and the ASCII data itself. If the logical channel number carries the value 63, the display message has to become visible on all receivers. Each logical channel has its own 2-bit DCI. The DCI is incremented when the ASCII display data of its corresponding logical channel has been changed. The ASCII display data consist of 12 characters and is 12 * 8-bit = 96-bit.