User manual

dCS 950 / 952 User Manual Manual for Software Version 6.2x
dCS Ltd 22
nd
May 2000
Manual part no: DOC0029526B1 Page 36 Document No: OS-MA-D0002-952.6B1
Contact dCS on + 44 1799 531 999 email to: [e-mail]
(inside the UK replace + 44 with 0) web site: www.dcsltd.co.uk
AES3 (AES/EBU) Format
Message Handling -
The AES/EBU interface accepts a data structure that conforms to the dCS
version of AES3-1992. This contains 28 bits of Manchester encoded data, and
a 4 bit near-Manchester encoded preamble in a subframe, and subframes are
further assembled in a block and frame structure. Each subframe contains:
• preambles, to allow the receiver to sync up
• up to 24 bits of audio data, transmitted lsb first
• V, a validity bit
• U, a user bit, for the "User Message"
• C, a Channel Status bit, for the "System Message"
• P, a parity bit
For more information on the way dCS implement the AES3 system message to
handle higher sample rates, see the Appendix to this manual. For the formal
definition of the AES3 interface, see footnote
6
, from the AES.
How Far will AES3 Go? -
The AES/EBU format was designed to go reasonable distances, at 44.1 kS/s
and 48 kS/s. Figure 15 and Figure 16 below show it over 16 m and 94 m using
average cables. The waveform at 94 m can still be decoded, although it is quite
degraded. Cable delay is about 5.6 ns/metre.
At 96 kS/s (twice the data rate the format was designed for) the allowed cable
length is less. Figure 17 and Figure 18 below show this over 16 m and 94 m. At
16 m the waveforms are still very good, but at 94 m they are really quite
unreliable.
We recommend restricting 96 kS/s cable runs to 20 m or less, and using good
cable near this length.
6
AES3-1992 (ANSI S4.40-1992) “AES Recommended practice for digital audio engineering – Serial
transmission format for two-channel linearly represented digital audio data”.