Digital Audio Interfacing and Networking 1473connector, either for all AES3 signals, or at least for
AES42 (AES3-MIC) digital microphone signals, but no
consensus has been reached. It should also be noted that
since the analog audio bandwidth usually does not
significantly exceed 20 kHz, and the AES3 spectrum
does not go below 100 kHz, it is possible for a single
cable to carry both an analog audio signal and an AES3
signal at the same time. The proposed modified XLR
connector could also allow such a dual use condition.
If Category 5 or greater UTP or STP is used, the
RJ45 connector must be used. Pins 4 and 5 of the RJ45
are the preferred pair, with pins 3 and 6 the suggested
alternative pair. It is suggested that if adaptors from
XLR to RJ45 are used, pin 2 of the XLR should connect
to pin 5 (or other odd numbered pin) of the RJ45, and
pin 3 of the XLR should connect to pin 4 (or other even
numbered pin) of the RJ45 connector.
39.4 AES-3id
AES-3id is a variant on AES3 where the signal is
carried over unbalanced 75: coaxial cable instead of
over 110: balanced cable. It can allow the transmis-
sion of AES3 information over distances of up to
1000 m. Analog video distribution equipment and cable
may often be suitable for transmission of AES-3id data.
This of course is a great convenience in video facilities.
At distances of up to 300 m, receiver equalization
may not be needed. Equalization must never be applied
at the line driver end.
The AES-3id information document provides exten-
sive tables and circuit diagrams showing active and
passive circuits for AES-3id transmission. Canare,
among others, sells passive adapters between 110:
balanced AES3 and 75: unbalanced AES-3id.
AES-3id was written based on the assumption of the
sampling rates specified in AES3-2003 and not on
double or quadruple rates as are sometimes used today.
The basic techniques of AES-3id should extend to these
higher rates, however.
The following information is based on
AES-3id-2001. It is always advisable to obtain the latest
revision of the information document.
39.4.1 Line Driver
AES-3id line drivers must have an impedance of 75:
and exhibit a return loss in excess of 15 dB from
100 kHz to 6 MHz. Obviously if frame rates in excess
of 48 kHz as allowed by AES3 were to be used, wider
bandwidths would be required. Much but not all modern
video gear will have the bandwidth to correctly handle
higher sampling rates.
The peak to peak output voltage into a 75:1%
tolerance resistor must be between 0.8 V and 1.2 V, with
a dc offset not to exceed 50 mV. The rise and fall times
should be between 30 ns and 44 ns. These output
voltage, dc offset, and rise and fall times have been
chosen for compatibility with analog video distribution
equipment. Lower dc offset values are desirable for
longer transmission distances.39.4.2 Interconnect SystemAES-3id cable must be 75r 3 : over the range from
100 kHz to 6 MHz. It is to be equipped with BNC
connectors as described in IEC 60169-8 but with an
impedance of 75: instead of 50:.39.4.3 Line ReceiverAES-3id line receivers must have an impedance of 75:
and exhibit a return loss in excess of 15 dB from
100 kHz to 6 MHz. The receiver must be capable of
correctly decoding signals with input levels of 0.8 V
and 1.2 V (measured peak to peak).
An AES-3id receiver must correctly interpret data
when a random data signal that is not less than
Vmin=320 mV and Tmin=0.5Tnom as shown in
Fig. 39-11 is applied to the receiver. For reliable opera-
tion at distances in excess of 1000 m, a receiver that
operates correctly with a Vmin= 30 mV may be required.Figure 39-11. AES-3id Eye diagram. Tnom = 0.5 unit interval
(UI) (see Fig. 39-5); Tmin = 0.5 Tnom; Vmin = 320 mV. The eye
diagram is one of the most powerful tools used to examine
the quality of received data. The larger the open area of the
eye the better. The limits shown are the most closed an eye
should ever be for correct reception of the AES-3id data.TminTnomVmin