1484 Chapter 39
39.6.1.1 Unbalanced Line
Connecting cables are unbalanced, shielded, with an
impedance of 75:r26.25: over the frequency range
from 100 kHz to 128 times the maximum frame rate.
The line driver has an impedance of 75:r 15 : at
the output terminals over the frequency range from
100 kHz to 128 times the maximum frame rate. The
output level is 0.5r0.1 Vp-p, measured across a
75 r1% : resistor across the output terminals without
any cable connected. The rise and fall times measured
between the 10% and 90% amplitude points should be
less than 0.4 UI. The jitter gain from any reference input
must be less than 3 dB at all frequencies.
The receiver should be basically resistive with an
impedance of 75:r5% over the frequency range from
100 kHz to 128 times the maximum frame rate. It
should correctly interpret the data of a signal ranging
from 0.2 to 0.6 Vp-p.
The connector for inputs and outputs is described in
8.6 of Table IV of IEC 60268-11, and popularly known
as the RCA connector. Male plugs are used at both ends
of the cable. Manufacturers should clearly mark digital
inputs and outputs.39.6.1.2 Optical ConnectionThis is specified in IEC 61607-1 and IEC 61607-2, and
popularly known as the TOSLINK connector.39.7 AES10 (MADI)The AES10 Standard describes a serial multichannel
audio digital interface, or MADI. The abstract says it
uses an asynchronous transmission scheme, but the
overall protocol is better described as isochronous. It is
based on the AES3 Standard, but allows thirty two, fifty
six, or sixty four channels of digital audio at a common
sampling rate in the range of 32 to 96 kHz, with a reso-
lution of up to 24 bits to be sent over a single 75:
coaxial cable at distances up to 50 m. Transmission over
fiber is also possible. Like the other schemes we have
looked at it only allows one transmitter and one
receiver.
Table 39-5 is based on AES10-2003. It is always
advisable to obtain the latest revision of the standard.
MADI used the bit, block, and subframe structure of
AES3 with the exception of the subframe preambles.
Instead it substitutes four bits according to Table 39-5.
MADI sends all its active channels in consecutive
order starting with channel zero. Each active channel
has the active channel bit set to 1. Inactive channels
must have all their bits set to 0 including the channel
active bit. Inactive channels must always have higher
channel numbers than any active channel.
The channels are transmitted serially using a nonre-
turn-to-zero inverted (NRZI) polarity free coding. Each
4 bits of the data are turned into 5 bits before encoding.Bit 4 5
State 0 0 Level II.
1 0 Level I.
0 1 Level III.
1 1 Reserved.
Bits 6–7 Reserved.
Byte 4—Word Length
Bit 0 Maximum audio word length.
0 Maximum 20 bit audio words.
1 Maximum 24 bit audio words.
Bits 1–3 Encoded audio word length.
Bit 1 2 3 Audio word length if
bit 0 indicates
max. 20 bit length.
State 0 0 0 Length not indicated,
default.
1 0 0 16 bits.
0 1 0 18 bits.
0 0 1 19 bits.
1 0 1 20 bits.
0 1 1 17 bits.
All other possible states of bits 1–3 are reserved and
are not to be used unless defined by the IEC in the
future.
Bits 4–7 Reserved.
Note 1. If the auxiliary sample bits are not used they should be set
to 0.
Note 2. Generally user data is not used and all bits are set to 0.
Note 3. Channel status is identical for all channels, with the
exception of the channel number if not set to all zeros (don’t
care).Table 39-4. IEC 60958 Edition 2 Standard
(Continued)Table 39-5. AES10 MADI
Bit Name Description Sense0 MADI channel 0 Frame synchronization bit 1 = true
1 MADI channel active Channel active bit 1 = true
2 MADI channel A or B AES3 sub-frame 1 or 2 1 = sub-
frame 2