1470 Chapter 39
Cabling to be used for AES3 is specified as 110:
balanced twisted pair with shield. The impedance must
be held over a frequency range from 100 kHz to 128
times the maximum frame rate to be carried. The line
driver and line receiver circuits must have an impedance
of 110:±20% over the same frequency range. While
the acceptable tolerance of the cable impedance is not
specified, it is noted that tighter impedance tolerances
for the cable, driver, and receiver will result in increased
distance for reliable transmission, and for higher data
rates. If a 32 kHz sampling rate mono signal were
carried in single channel double sampling frequency
mode, the interface frequency range would only extend
to 2.048 MHz. If a 48 kHz sampling frequency
two-channel signal were to be carried, the interface
frequency range would extend to 6.144 MHz, or about
the 6 MHz bandwidth commonly quoted for AES3.
However, if a 192 kHz sampling frequency two-channel
signal were to be carried, the interface frequency range
would extend to 24.576 MHz. As you can see, some
uses of AES3 can extend the frequency range far
beyond 6 MHz. If you are using a mode that has
extended interface frequency, make sure that the trans-
mitter, interconnect system, and receiver are all
designed to meet specifications over the entire
frequency range in use.
When AES3 was originally introduced it was
thought that ordinary analog audio shielded twisted pair
cable would be acceptable for carrying AES3 digital
audio, and indeed that is often the case for shorter
distances. However, the impedance and balance of
common audio cable vary widely, and it was quickly
determined that purpose built AES3 cable performed
significantly better for AES3 than ordinary analog audio
cable. It was later determined that such AES3 rated
cable often also performed significantly better as analog
audio cable than ordinary cable, so today we commonly
see AES3 rated cable used in both analog and digital
applications.
While the AES3 Standard makes mention of inter-
connect lengths of “a few hundred meters,” in practice
distances beyond about 100 m often require the use of
equalization to compensate for losses in the cabling. If
such equalization is used, it must never be applied to the
transmitter, but only to the receiver.
As an alternative to purpose built AES3 rated digital
audio cable, structured wiring meeting Category 5 or
greater is acceptable. Such cabling can be of either
shielded twisted pair (STP) or unshielded twisted pair
(UTP) construction. To deliver satisfactory perfor-
mance, only one cable type (Category 5 or higher STP,
Category 5 or higher UTP, or AES3 digital audio rated)Bits 0–7 Reserved. Set to 0 unless defined in the future by the
AES.
Bytes 6–9
Alphanumeric channel origin data. Byte 6 contains
the first character.
Bits 0–7
(each
byte)7 bit International Organization for Standardization
(ISO) 646, American Standard Code for Information
Interchange (ASCII), data. No parity bit is used. Bit 7
is always 0. Transmit LSBs first. Nonprintable char-
acters (codes 01 to 1F hex and 7F hex) must not be
used. Default is all 0’s (code 00 hex or ASCII null).
Bytes 10– 13
Alphanumeric channel destination data. Byte 10 con-
tains the first character.
(each
byte)7 bit ISO 646 ASCII data. No parity bit is used. Bit 7
is always 0. Transmit LSBs first. Nonprintable char-
acters (codes 01 to 1F hex and 7F hex) must not be
used. Default is all 0’s (code 00 hex or ASCII null).
Bytes 14– 17
Local sample address code sent as 32 bit binary with
LSBs first. Value is of the first sample in this block.
Bits 0–7
(each
byte)Transmit LSBs first. Default is all 0’s.Note 1. This serves the same function as an index counter on a
recorder.
Bytes 18– 21
Time of day sample address code sent as 32 bit binary
with LSBs first. Value is of the first sample in this
block.
Bits 0–7
(each
byte)Transmit LSBs first. Default is all 0’s.Note 1. This time of day is the time of the original analog to digi-
tal conversion, and should not be changed thereafter. Midnight is
represented by all 0’s. In order to convert this sample code into
correct time, the sampling frequency must be known accurately.
Byte 22
Flag bits used to indicate if the contents of the chan-
nel status data are reliable. If the specified bytes are
reliable then the associated bits are set to 0. If the
bytes are unreliable, the associated bits are set to 1.
Bits 0–3 Reserved. Set to 0.
Bit 4 Bytes 0 to 5
Bit 5 Bytes 6 to 13
Bit 6 Bytes 14 to 17
Bit 7 Bytes 18 to 21
Byte 23
Channel status data Cyclic Redundancy Check Char-
acter (CRCC).
Bits 0–7 The CRCC allows the receiver to check for cor-
rect reception of the bytes 0 through 22 of the
channel status block. It is generated by
G(x) = x^8 +x^4 +x^3 +x^2 + 1. If a “minimum”
implementation is done, this will default to all
0’s. The AES3 Standard provides further infor-
mation on how to calculate this.Table 39-1. Channel Status Data Format Details
(Continued)