# IEC 61937-12:2010 pdf – Digital audio – Interface for non-linear PCM encoded audio bitstreams applyingIEC 60958- Part 12: Non-linear PCM bitstreams according to the DRA formats

IEC 61937-12:2010 pdf – Digital audio – Interface for non-linear PCM encoded audio bitstreams applyingIEC 60958- Part 12: Non-linear PCM bitstreams according to the DRA formats.

EXAMPLE The receiving delay time to receive a whole data-burst with maximum length is calculated as follows, The length of preamble is 64 bits. The maximum length of whole data payload is 4 096 bit for a maximum bit rate of 192 kbitls. In this case, the maximum length of data-bursts is 4 160 bits. The receiving delay is 2.708 ms (4 160 x 2148/64) at 48 kHz sampling frequency. The decoding delay is 21.333 ms, corresponding to one ORA frame. Hence, the latency of DRA decoding is approximately 24.041 ms.

The absolute maximum length of the data-burst is calculated as follows. Each data-burst contains a minimum of 4 stuffing 16-bit words. The repetition period of data-bursl is 1 024 IEC 60958 frames. Therefore, the maximum length of data-burst leads as follows:

1 024 samples x 2 channels x 16 bits — 4 words x 16 bits = 32 704 bits

The receiving delay time is 21,292 ms (32 704 x 2/4864) at 48 kHz sampling frequency, which leads to the absolute maximum DRA decoding latency of 42.625 ms with the decoding delay 21,333 ms as above.

5.3.2 DRA half-rate low samplIng frequency condition

53.2.1 Data for DRA half-rate low sampling frequency

The streams of the data-bursts for DRA half•rate low sampling frequency consist of sequences of DRA half-rate low sampling frequency frames. The data-type and sub-data-type of a DRA databurst are 23 and 3 respectively with the bits 8-9 of Pc equal to 012. The data- burst is headed with a burst.preamble. followed by the burst.payload, and stuffed with stuffing bits. The burst-payload of each data•burst of DRA halt•rate low sampling frequency data shall contain one complete DRA half-rate low sampling frequency frame and represents 2 048 samples for each encoded channel. In the context of this standard, forms relating to half -rate low sampling frequency mean the sampling frequency of the lEG 60958 frame (I.e.. IEC 60958 frame rate) increases to 2 x original sampling frequency for DRA encoding process. The units of length-code (Pd) shall be In bytes.

The reference point of a DRA half -rate low sampling frequency data-burst is be 0 of Pa and occurs exactly once every 2 048 sampling periods. The data-burst containing DRA half-rate low sampling frequency frames shall occur at a regular rale, with the reference point of each DRA half.rate low sampling frequency data-burst beginning 2 048 IEC frames after the reference point 01 the preceding DRA halt-rate low sampling frequency burst of the same bitstream number.

It is recommended that pause data-bursts are used to till stream gaps in the DRA half-rate low sampling frequency bitstream as described in IEC 61937-1. and that pause data-bursts be transmitted with a repetition period of 64 lEG 60958 frames, except when other repetition periods are necessary to fill the precise stream-gap length, which may not be a multiple of 64 EC 60958 frames, or to meet the requirement on burst spacing of lEG 61937.

When a stream gap in a DRA halt-rate low sampling frequency stream is tilled by a sequence of pause data-bursts, the Pa of the first pause data-burst shall be located at 2 048 sampling periods following the Pa of the previous DRA half-rate low sampling frequency frame. It is recommended that the sequence(s) of pause data-bursts which fill the stream gap should continue from this point up to (as close as possible to, considering the 64 lEG 60958 frame length of the pause data-burst) the Pa of the DRA half-rate low sampling frequency data-burst which follows the stream gap. The gap-length parameter contained in the pause data-burst is intended to be interpreted by the DRA decoder as an indication of the number of decoded PCM samples which are missing, due to the resulting audio gap.

5.32.2 Latency of DRA decoding half-rate low sampling frequency

The latency of an external audio decoder to decode DRA at half.rate low sampling frequency Is defined as the sum of the receiving delay time and the decoding delay time.