User Manual

24
User’s Guide OctaMic XTC © RME
10. Using Multiple Units with MADI
Devices like the OctaMic XTC can be connected serially via MADI, and then transmit up to 64
channels (with up to 8 XTC) over one single MADI cable. In the menu Digital Routing the user
can decide at which place of the 64-channel MADI stream the current eight channels of the XTC
are inserted.
When multiple devices are connected serially, the MADI I/O of each unit causes a delay of sev-
eral samples. This problem is solved by the function Delay Compensation. Its settings are found
in SETUP – Options – MADI Settings.
10.1 Delay Compensation
Default: Off. Available settings: Off, Manual, Auto-ID, Auto-CA
When multiple devices are connected serially, the MADI I/O of each OctaMic XTC causes a
delay of 3 samples. Therefore at the MADI output of the last device, the data of all upstreamed
devices are delayed. At Double Speed the delay rises to 6 samples per unit, at Quad Speed to
12 samples.
Delay Compensation delays the signals in a way that they are sample-synchronous in multi-
device operation.
Delay Compensation has to be manually activated in each unit!
The following table lists the delay in samples from two up to eight units connected serially.
When using four units, the data of the first unit are delayed by 9 samples to the last unit, the
units 2 and 3 are delayed by 6 and 3 samples respectively. At Double Speed and Quad Speed
the values rise. Please note that in Double Speed no more than four, in Quad Speed no more
than two OctaMic XTC can be used serially with MADI.
Units Delay Delay DS Delay QS DC DC DS DC QS
2 3 6 12 21 18 12
3 6 12 - 21 18 -
4 9 18 - 21 18 -
5 12 - - 21 - -
6 15 - - 21 - -
7 18 - - 21 - -
8 21 - - 21 - -
Inputs and outputs are delayed in different ways. With the inputs the delay equals the values
shown in the table. When using multiple units in serial cabling, the input data of the second unit
is delayed by 3 samples, the input data of the third by 6 samples and so on. This way, at the
end of the chain all input data are sample-aligned again. Chapter 13.3 shows a diagram to illus-
trate the setup.
The XTC’s Delay Compensation affects not only the analog inputs, but the digital ones as well.
For example additional AD-converters connected to the ADAT inputs and inserted into the
MADI stream – all the converters analog inputs fed to multiple XTCs will be sample-aligned
again.
Even the analog outputs of the XTC use the Delay Compensation. For technical reasons here
the delay is a fixed constant of 21 samples in Single Speed, no matter how many devices are
connected serially. In Double Speed the delay is 18, in Quad Speed 12 samples. The in most
cases slightly increased delay is outweighed by the big advantage of sample-aligned analog
outputs across multiple units.
21 samples @ 48 kHz
equal 437 µs.
18 samples @ 96 kHz
equal 187 µs.
12 samples @ 192
kHz equal 62.5 µs.