IEC 61937-14:2017 pdf download

IEC 61937-14:2017 pdf download.Digital audio – Interface for non-linear pcm encoded audio bitstreams applying IEC 60958
1 Scope
This part of IEC 61 937 describes the method to convey non-linear PCM bit streams encoded according to the AC-4 format.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements 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 60958 (all parts), Digital audio interface IEC 61 937-1 :2007, Digital audio interface for non-linear PCM encoded audio bitstreams applying IEC 60958 – Part 1: General IEC 61 937-1 :2007/AMD1 :201 1 , Digital audio interface for non-linear PCM encoded audio bitstreams applying IEC 60958 – Part 1: General IEC 61 937-2, Digital audio interface for non-linear PCM encoded audio bitstreams applying IEC 60958 – Part 2: Burst Information ETSI TS 1 03 1 90 v.1 .1 .1 , 201 4, Digital Audio Compression (AC-4) Standard
3 Terms, definitions and abbreviated terms
For the purpose of this standard, the following definitions and abbreviations apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: • IEC Electropedia: available at http://www.electropedia.org/ • ISO Online browsing platform: available at http://www.iso.org/obp 3.1 AC-4 frame AC-4 sync frame, as specified in Annex A 3.2 audio frame rate number of AC-4 audio frames per second, indicated by the value of the frame_rate_index AC-4 bit stream parameter as specified in ETSI TS 1 03 1 90 3.3 base sampling frequency sampling frequency of the AC-4 bit stream, indicated by the value of the fs_index AC-4 bit stream parameter as specified in ETSI TS 1 03 1 90 Note 1 to entry: AC-4 supports base sampling frequencies of 44.1 and 48 kHz only. 3.4 latency delay time of an external audio decoder to decode an AC-4 data burst defined as the sum of two values: the receiving delay time and the decoding delay time 3.5 fractional frame rates fractional audio frame rates supported by AC-4 Note 1 to entry: These frame rates are written in shorthand notation, as specified in Table 1 .
5 Format of AC-4 data-bursts
5.1 General This clause specifies the AC-4 audio data-burst. Specific properties such as reference points, repetition period, the method of filling stream gaps, and decoding latency are specified. The decoding latency (or delay), indicated for the data-type, should be used by the transmitter to schedule data-bursts as necessary to establish synchronization between picture and decoded audio. 5.2 Pause data-burst The pause data-burst for AC-4 is given in Table 3.5.3 Audio data-burst 5.3.1 The AC-4 data An AC-4 bit stream consists of a sequence of AC-4 frames. The AC-4 data-burst is headed with a burst-preamble, followed by the burst-payload. The structure of the AC-4 data-burst is shown in Figure 1 . The data-type bits 0-4 of an AC-4 data-burst is 24, and the data-type bits 5-6 is 0. When AC-4 data is being transmitted, the transmission device shall ensure that both the data-type bits 0-4 and data-type bits 5-6 values are set correctly. Additionally, the receiving device shall utilize both the data-type bits 0-4 and data-type bits 5-6 values to ensure that the content of the data-burst is correctly identified as AC-4.The AC-4 burst-payload shall always contain a single AC-4 frame. The transmission device shall ensure that the AC-4 burst-payload is constructed only from a single complete AC-4 frame. It is prohibited to transmit a single AC-4 frame using multiple data-bursts. The length of the AC-4 data-burst will depend on the encoded bit rate (which determines the AC-4 frame length). The AC-4 bit stream is specified in ETSI TS 1 03 1 90. The reference point of an AC-4 data-burst is bit 0 of Pa. The repetition period of the AC-4 data-burst shall be defined by the base sampling frequency (indicated by the value of the fs_index AC-4 bit stream parameter as specified in ETSI TS 1 03 1 90) and frame rate (indicated by the value of the frame_rate_index AC-4 bit stream parameter as specified in ETSI TS 1 03 1 90) of the AC-4 audio bit stream. The IEC 60958 frame rate shall be equal to the base sampling frequency of the AC-4 bit stream. As AC-4 supports multiple audio frame rates that match commonly used video frame rates, the transmission device shall ensure that the selected AC-4 data-burst repetition rate is equal to the duration of the AC-4 frame, as specified in Table 5.