BS EN 61937-10:2011 pdf download

BS EN 61937-10:2011 pdf download.Digital audio — Interface for non-linear PCM encoded audio bit streams applying IEC 60958 Part 10: Non-linear PCM bitstreams accordingto the MPEG-4 Audio Lossless Coding (ALS)format.
The regular rate of the MPEG-4 A1.S frames and the repetition period of the data burst can be calculated as
The value of the samples field is stored in the 9th to 12th bytes of the MPEG-4 ALS burst- payload. The value represents the number of samples contained in the MPEG-4 ALS burst- payload. The IEC 60958 frame rate is defined by the audio sampling rate and a value of the multiplier (see Table.2).
The reference point of a MPEG-4 ALS data-burst is bit 0 of Pa and occurs exactly once every predefined number of IEC 60958 frames. The data-burst containing MPEG-4 ALS frames shall occur at a regular rate, with the reference point of each MPEG-4 ALS data-burst beginning alter the number of IEC 60958 frames In the previous MPEG-4 ALS data-burst from the reference point of the preceding MPEG-4 ALS data-burst (of the same bit-stream-number).
It is recommended that pause data-bursts be used to fill stream gaps in the MPEG-4 ALS bit stream as described in the IEC 61937-1, and that pause data-bursts be transmitted with a repetition period of 32 IEC 60958 frames, except when other repetition periods are necessary to fill the precise stream gap length (which may not be a multiple of 32 IEC 60958 frames), or to meet the requirement on burst spacing (see IEC 61937-1).
When a stream gap in an MPEG-4 ALS stream is filled by a sequence of pause data-bursts, the Pa of the first pause data-burst shall be located after a number of sampling periods represented by the samples’ field of the ALSSpecificConfig header in the previous MEG-4 ALS data-burst from the Pa of the previous MPEG-4 ALS frame, It is also recommended that the sequence(s) of pause data-bursts that fill the stream gap should continue from this point up to (as close as possible, considering the 32 IEC 60958 frame length of the pause databurst) the Pa of the first MPEG-4 ALS data-burst that follows the stream gap. The MPEG-4 ALS decoder can detect the number of decoded PCM samples by using the value set in the sam pIes field of ALSSpeciflcConfig.
The receiving delay time to receive a whole data-burst Is calculated by using the length of the burst- payload. Nd. which Is shown in Figure 3. The length o1 preamble is 8 bytes. Since an IEC 60958 frame can contain 4 bytes, The receiving delay of an MPEG-4 ALS data-burst should be as follows:
The maximum receiving delay time is related to the number of samples contained in the data-burst and to 12 bytes of the the IEC 60958 frame rate. The number of samples. ‘samples, is stored In the 9
ALSSpecificConfig header of the MPEG-4 ALS burst-payload (131i to 16 bytes of the MPEG-4 ALS burst-payload) as shown in Figure 3. The maximum decoding delay time can be regarded as being the same as the maximum receiving delay time,
Note that the encoded size never exceeds the rate given by the IEC 60958 frame rate in theory except when the Aux data in burst is too large The Aux size shall be small enough to ensure that the total size of the burst compiles with following formula:
Pd <= ((((samplesji(samp freqj) (IEC 60958 frame ratel x 4 bytes) — 8 bytes)18 EXAMPLE The maximum size of the MPEG-4 ALS burst-payload shall be equal to or less than the size calculated by the frame repetitIon p6 hod and the IEC 60958 frame rate. When the values of samp_treq’, ‘samples, channels’, and ‘resolution’ are 48 000. 2 048, 1 • arid I respectively, the sampling rate of the audio signal is 48 kHz. the number of samples contained in the MPEG-4 ALS burst-payload is 2 048 samples, the number of channels is 2 (=‘channels’+l), and the number of bits per an audio sample is 16 bits. With these values, the IEC 60958 frame rate is 96 kHz as shown in Table 2. Though the receiving delay time vanes depending on the compressed size of the MPEG-4 ALS burst-payload, the maximum receiving delay time can be calculated by using ‘samples’ and ‘samp_freq’. In this example case, It should be 42,67 ms (2 048)48 000 = 0.042 67). The maximum decoding delay time should be 42.67 ms because it can be regarded as being the same as the maximum receiving delay time. The total latency of MPEG-4 ALS decoding is approximately 65.34 ms.