Instruction manual

Euphonix FT730 FiberTran Fiberoptic Extender Operation Manual

Technical Reference

Synchronization for Distances Over 800 ft (250 m)

MADI utilizes a polarity-free, serial NRZI (non-return-to-zero inverted) protocol

with encoding at 125 Mbit/s (±100 ppm). Sample timing is controlled independently

by distributing a master synchronization signal. Originally, the transmission medium

was 75-Ω coaxial cable. There are two important synchronization issues:

• The MADI signal’s transmitted frame start time must be within 5% of the

sample period time determined by the synchronizing signal.

This requirement is usually met by the circuit design using the distributed syn-

chronization signal.

• The received frame start time must be within ±25% of the sample period

reference time.

This requirement is governed by physics: it is the time of flight (delay time) dif-

ference between the sample start and the start of the frame. The speed of light

(299,792,458 m/s) and the propagation speed of the transmission medium gov-

ern this delay time.

Transmission mediums, such as fiber and coaxial cable, have propagation speeds in the

range 60–70% of the speed of light. This does not present a problem when MADI and

the synchronization signal are sent together to a destination, such as a MA703. The

problem manifests when MADI is used to return data from a source such as an AM713,

where the delay time difference for the MADI and synchronization signals exceeds the

received frame start time requirement (±25% of the sample period reference time).

The FT730 has two types of synchronization outputs:

AES/Sync or Word Out is used for devices receiving MADI at the remote end. These

outputs are used if the signal meets the criteria stated in the first bullet above.

Retimed AES or Retimed Word Sync is used for devices transmitting MADI to the

local end. The control/sync fiber pair is used to measure at the local end by comparing

the local sync timing with that returned from the remote end. This number is sent to the

remote end where the timing is adjusted in sixteenth frame increments to keep it within

the operational requirements stated in the second bullet above.