The electrical parameters of AES3 are based upon those specfied in CCITT V.11. To further improve the transmission integrity, a circuit such as shown in fig. 4 is recommended, but not required. The transformer is used to isolate the signals, preventing ground loops and reducing electromagnetic interference, and the series capacitors protect the transformer in case of connection to a surge containing a high DC voltage. The differential signal amplitude was specified as 3 to 10 volts peak-to-peak in AES3-1985, measured across the 110 ohm characteristic impedence (implementations using single 5 volts supply, AES3-1992 reduced the signal range to 3 to 7 volts peak-to-peak).
Fig. 4 - AES/EBU Transmission and Reception Recommended Circuits
Three implementation of the Channel Status block are specified in AES3-1992, the minimum, standard, and enhanced implementations.
The minimum implementation set the first bit of the block, called byte 0 bit 0, to one (1) to indicate professional usage of the Channel Status block and all other bits of the Channel Status block are set to zero (0).
The standard implementation will also set byte 0 bit 0 and will correctly encode and recognize all Channel Status bts in byte 0, 1, 2 and 23. Byte 23 is the CRC byte.
The enhanced implementation is defined as any implementation exceeding the standard implementation whether or not it encodes and recognizes all the other Channel Status bytes.
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