Word Clock, BNC T-splitter or distribution box?

[friction909]

At what point would it be a good idea to use some sort of word clock distribution system? How many devices can you safely chain together using BNC T-splitters? I would like to sync three devices together, a Crane Song HEDD 192, a LynxTwo and a Metric Halo 2882, where the HEDD is the master clock.

Another question that I'm having difficulty finding an answer to: does external clocking impact A/D conversion, D/A conversion or both? From reading various things I get the impression that A/D conversion IS impacted by external word clock and D/A is clocked by the clock imbedded in the digital signal and is not impacted by word clock carried on a separate BNC clock cable. Is this true?

The reason I'm asking is that I will be using the HEDD for (virtually) all A/D conversion and the LynxTwo and Metric Halo are for extra D/A (analog stem mixing) and the interface(s) to the computer. Do I even need to sync all three together if only the HEDD is used for A/D?

Ultimately I'm trying to determine if I should spend money on a word clock distributor, or a master clock with lots of clock outputs, taking into account that the HEDD connected to the LynxTwo or the Metric Halo will be doing most of the A/D and D/A work.

Thanks,
Robert

[klaukholm]

T connectors will be fine.
I always clock from the most important AD when possible.
From there I go the shortest route for the BNC cables.

[Jim vanBergen]

Daisy chaining works for me for two or three units, max.

There is no real "standard" for word clock, so I'd call Crane Song and see what they think about how robust the word clock is when daisy chained.

When I got outside a couple of devices (remote truck, larger installs) I found the word clock degraded significantly and the presence of a VDA (video distribution amplifier, which is a pretty straightforward circuit, and inexpensive) made a large sonic impact.

Try without, eventually you may find the same results I did. Yamaha originally specified military-spec T's for word clock; I had so many issues with seven different PM1D consoles using the T method that I will only use the desk with a proper VDA providing clock distribution. It's actually cheaper than mil-spec T's.

Jim

[dkatz42]

Originally Posted by friction909

does external clocking impact A/D conversion, D/A conversion or both? From reading various things I get the impression that A/D conversion IS impacted by external word clock and D/A is clocked by the clock imbedded in the digital signal and is not impacted by word clock carried on a separate BNC clock cable. Is this true?

It depends on how you configure the DAC (and what its capabilities are.) A DAC can potentially pick up embedded clock from AES or lightpipe or MADI, or it can use word clock, or it can use an internal clock. The key is that everything in the digital chain has to derive its timing from the same clock.

The right strategy depends on a number of things. The goal is to minimize jitter (which is *only* an issue at the D/A stage, not in the digital interconnects.) If you have a good quality DAC with good clocking, using internal clocking (and sending word clock from the DAC to any upstream digital boxes) is usually best, all other things being equal. Cheap converters may benefit from external clocking.