AES/EBU/SPDIF Formats
C-10 ADSP-214xx SHARC Processor Hardware Reference
There is one channel status bit in each sub-frame, (comprising of 192 bits
per audio block). This translates to 192/8 = 24 bytes available (per audio
block). The meaning of the channel status bits are as follows
• The biphase encoded AES3 stream is composed of subframes
(Figure C-5 on page C-13). Subframes consist of a preamble, four
auxiliary bits, a 20-bit audio word, a validity bit, a user bit, a chan-
nel status bit, and a parity bit.
• The preamble indicates the start of the subframe. The four auxil-
iary bits normally are the least significant bits of the 24-bit audio
word when pasted to the 20-bit audio word. In some cases, the aux-
iliary bits are used to convey some kind of other data indicated by
the channel status bits.
• The validity bit (if cleared, =0) indicates the audio sample word is
suitable for direct analog conversion. User data bits may be used in
any way desired by the program. The channel status bit conveys
information about the status of the channel. Examples of status are
length of audio sample words, number of audio channels, sampling
frequency, sample address code, alphanumeric source, and destina-
tion codes and emphasis. The parity bit is set or cleared to provide
an even number of ones and of zeros for time slots 4-31.
• Each frame in the AES3 stream is made up of two subframes. The
first subframe is channel A, and the second subframe is channel B.
A block is comprised of 192 frames. The channel status is orga-
nized into two 192 bit blocks, one for channel A and one for
channel B. Normally, the channel status of channel A is equal to
channel B. It is extremely rare that they are ever different. Three
different preambles are used to indicate the start of a block and the
start of channel A or B.
1. Preamble Z indicates the start of a block and the start of subframe
channel A
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