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dCS 954 User Manual Manual for Standard Software Version 1.5x
dCS Ltd June 2000
Manual part no: DOC136954 iss 2B1
Page 49
file 135954ma2b1.pdf available from website
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dCS
on + 44 1799 531 999 email to: more@dcsltd.co.uk
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AES3 (AES/EBU) Format
Message Handling -
The AES/EBU interface decodes 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
The message attached to the AES Reference Out depends on the Ref In
setting. In Loop or Loop.t modes, it is copied from the Reference In data.
When set to Route, the message is copied from the lowest numbered AES
input selected. When set to ddC with a PCM input, the message is as follows:
Professional: On
Emphasis: Off
Non-Audio: Off
Mode: Not indicated
Sample rate: (Correctly stated)
Source: DCS1
Destination: null
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 28 and Figure 29 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 30 and Figure 31 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”.