IEC 60958-4-2:2016 pdf download – Digital audio interface – Part 4-2: Professional applications – Metadata and subcode.
1 Scope This part of IEC 60958 specifies the format for coding metadata, or subcode, that relates to the audio content and is carried with it. This part of IEC 60958, together with IEC 60958-1 , IEC 60958-4-1 , and IEC 60958-4-4, specifies an interface for serial digital transmission of two channels of periodically sampled and linearly represented digital audio data from one transmitter to one receiver. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60958-1 :2008, Digital audio interface – Part 1: General IEC 60958-1 :2008/AMD1 :201 4 IEC 60958-3, Digital audio interface – Part 3: Consumer applications IEC 60958-4-1 , Digital audio interface – Part 4-1: Professional applications – Audio content IEC 60958-4-4, Digital audio interface – Part 4-4: Professional applications – Physical and electrical parameters ISO 646, Information technology – ISO 7-bit coded character set for information interchange ITU-R Recommendation BS.450, Transmission standards for FM sound broadcasting at VHF 1 ITU-T Recommendation J.1 7, Pre-emphasis used on sound program circuits 3 Terms, definitions and abbreviations 3.1 Terms and definitions For the purposes of this document, the terms and definitions given in IEC 60958-1 and the following apply.
4 User data format One bit of user data may be carried in each subframe. Different user data may be carried in each channel and may be related to the associated audio or not. Its capacity in kbit/s is therefore equal to the sampling frequency in use, in kilosamples/s, for each channel. User data bits may be used in any way desired by the user. Known possible formats for the user data channel are indicated by the channel status byte 1 , bits 4 to 7. Other possible formats may be used and may or may not be standardized in future. The default value of the user data bit is logic 0. 5 Channel status format 5.1 Channel status bit One bit of channel status data shall be carried in each sub-frame. Different channel status data may be carried in each channel. Their capacity in kbit/s is therefore equal to the sampling frequency in use, in kilosamples/s. NOTE The channel status for each audio signal carries information associated with that audio signal, and thus it is possible for different channel status data to be carried in the two subframes of the digital audio signal. Examples of information to be carried in the channel status are: length of audio sample words, number of audio channels, sampling frequency, sample address code, alphanumeric source and destination codes, and emphasis. 5.2 Channel status block Channel status information shall be organized in 1 92-bit blocks, subdivided into 8-bit bytes numbered from 0 to 23. The transmission format shall mark every 1 92 nd frame to show that it carries the first bit of a block. Within each byte, the bits are numbered from 0 to 7, 0 being the first bit transmitted, so bit 0 of byte 0 is the first bit in the block. Where a byte holds a numerical value, bit 0 is the least significant bit. NOTE In IEC 60958-1 , the frame that begins with preamble Z contains the first bit of a block in both channels. In other transports (for example AES1 0 and IEC 62365) a block start flag is used to mark the first subframe in a block, and may be applied to each channel independently.
5.3 Implementation 5.3.1 Implementation levels 5.3.1 .1 General The following two implementations are defined: standard and enhanced. These terms are used to communicate in a simple manner the level of implementation of the interface transmitter involving the many features of channel status. Irrespective of the level of implementation, all reserved states of bits defined in 5.5 shall remain unchanged. 5.3.1 .2 Standard level The standard implementation provides a fundamental level of implementation which should prove sufficient for general applications in professional audio or broadcasting. In standard implementation, transmitters shall correctly encode and transmit all channel status bits in byte 0, byte 1 , byte 2, and byte 23 (CRCC) in the manner specified in this standard. NOTE This note applies to the French language only.