A p p l i c at i o n N ot e

MADI
Multi Channel Audio Digital Interface
Development of the MADI-Interface was under leadership ofSony, Mitsubishi, SSl and Neve. Later it was standardised by
the AES (Audio Engineering Society) as AES-10. This interface
transmits up to 56 channels via 75 Ohm coax cable or alternatively through optical fibre cable.
Specifications• 56 channels• audio data up to 24 bit / 44.1kHz to 48 kHz (+12.5%)• channel data are in 100% compatibility to the AES3 interface(channel status, user data)
Coax cable• cable length: 50 m
• impedance: 75 Ohm (± 2 Ohm)
• levels: 300 600 mVpp (at 75 Ohm)
Optical cable• cable length: up to 2 km
• wavelength: 1300 nm (invisible infrared)

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Functionality
All MADI channels are transmitted synchronously, so bit clock andword clock of all channels have to be identical.
As with the AES/EBU the MADI interface structures data into subframes and frames. But here the frame consists of 56 subframes.
Each subframe contains one of the 56 channels with it‘s audio andassociated channel status and user data. Thus MADI can transmit
28 AES/EBU channel pairs.

Only difference to AES/EBU within a MADI subframe is significance of the first 4 bits. In contrast to AES/EBU, where these 4bits contain the preamble, here they transmit the following:

Sync

Meaning

RemarkBit 0mark for channel 0

1 for fist channel,
otherwise 0

Bit 1

channel on/off

active channels marked
with 1Bit 2channel A/B

marking of a stereo
channel (A = 0)

Bit 3channel status .
block sync

marks the start of a newchannel status block (192Bit)

MADI transmits with fixed data rate of 125 Mbit/s. On the other
hand 56 channels with 32 bit/subframe and 48k subframes/s perchannel result in a total data rate of 56* 32* 48 kbit/s = 86 Mbit/s.
Taking into account the varipitch option, which allows sample
rates to be increased up to 12.5% from it‘s nominal value, thisresults in a maximum bit rate of 97 Mbit/s. MADI uses a special
bit coding scheme were 4 bits a represented by 5 bits. This coding
scheme increases the data rate to 121 Mbit/s. Not used capacity
is filed up with padding words which are used to channels synchronization purposes.

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Not taking advantage from the varipitch option the numberof audio channels can be augmented to 64 channels (98.304
Mbit/s). This is possible without leaving compatibility to theMADI transmission standard. Chaining up devices mastering the 64 channel operation mode with those just operating in the standard mode only 56 channels are available.

Figure:Example for a bi-directional, 64 channel ADAT to MADI Interface.

If ever possible cabling between MADI devices is accomplishedredundantly, which means two cables are installed instead of justone. This prevents from all 56 or even 64 channels to be lost incase of cable rupture. To enable the redundancy some devices
dispose of two transmitter- and two receiver interfaces. In caseof cable failure these devices switch automatically to the secondline.
In comparison to other interfaces coding complexity of the MADI
interface is clearly increased. Therefore as a rule this interface isencountered only in upper price range devices.

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