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Topic: Word Clock Troubles

  1. #1

    Word Clock Troubles

    Hi friends,

    Can anyone of you maybe give me a good link on the web for a detailed "howto" for hooking up 4 PC's via word clock?

    I can't find anything on max cable lengths etc.

    This is a short description of my puzzle:

    In my former office/studio room I had only my DAW in my working room and 3 Giga PC's in a nearby hallway. Word clock cable of 10 meters to the Giga PC's, daisy chained. Please note: wrong impedance (50 instead of 75 ohms) and no terminators. Output via 3 Adat cables back to the DAW, into Logic 5.5.

    Absolutely no syncing problems, in spite of the incorrect impedance...

    Now, in my new appartment, the cable length is 18 meters, instead of 10 and I just can't get my stuff working without a LOT of clicks and often constant noise.

    The DAW HDSP 9652 dialog politely tells me "Sync" for all 3 Giga's, but my mixer and speakers tell me a different story.

    I started (again) with an incorrect impedance cable of 50 Ohm. Problems. So I replaced that one with a very high quality cable of 75 Ohms. Tried every order of daisy chaining, but there is always at least on PC giving lots of noise, and the others intermittent clicks...

    Do I need to hire some technician with an oscilloscope and "really" good cables?

    This is driving me nuts, replaced cables several times (a lot of work, because they are nicely hidden and run to a closet 10 meters from my desk... Applied terminators, no terminators, no difference.

    My audio cards are:
    "Elfman": RME HDSP 9652 (DAW)
    "Zimmer": RME Digi96/8
    "Silvestri": RME Hammerfall 9652
    "Williams": RME Hammerfall 9652

    Pretty good cards, in my experience.

    PC's are all Athlon's, 3000, 2600, 2200 and 1800.

    Would it be possible that there is an interaction between the WC pulses and the length of my Adat cables? I heard that 18 meters (custom made for me) is quite long for Adat.

    Any comment is more than welcome!


  2. #2

    Re: Word Clock Troubles

    Hmmm- it's strange because this is almost what one would have expected the first time around (when you were daisy chaining all 4 machines with incorrect impedance). I'm almost more puzzled as to why that worked VS. why this revised setup in the new pad isn't working. I'm no expert on this, but I have 4 digital devices word clocked and was told, in no uncertain terms, that daisy chaining beyond two devices gets you into "iffy" territory. BTW I also use RME cards, and have great things to say about those, so I don't think this is a problem at the component level, rather the overall design. I opted to employ an Apogee Big Ben, and invested in high-grade 75ohm cables from Apogee as well. Everything runs very very smooth with room to grow. I might suggest that you at least try that kind of unit (typically can be bought with a return policy) JUST to verify that the determine whether your root cause is the attempt to daisy chain in the first place. If the problem repeats with a purpose-built external clock, then there's something going on beyond the word clock. I do know that RMEs don't handle error correction very well because it so happened that before I did this, my digital mixer was the clock master and its word out went on the fritz. The RME had all sorts of problems with that DESPITE stil showing as synced. But once I employed the Apogee, it's been great ever since.

  3. #3

    Re: Word Clock Troubles

    Thanks for the reply,

    I have posted my puzzle on more forums and got quite a few nice tips, but I am still not sure where to look first. I can drive 1 Giga PC nearly flawlessly (occasional click), daisy chaning to others, in any order gives serious problems. Seems to point to the daisy chaining indeed. However, I have also been told that my Toslink/Adat cables are too long (18 m) in order to operate without problems. What do you think? If one or any of my machines can run OK, the lightpipes are working? Or can they still play a role in the overall problem? I was already looking for lightpipe amps...

    Anyone else who has bad experiences with daisy chaining devices with BNC W/C cables? I thought this was just THE approach to connect multiple audio devices...

  4. #4

    Re: Word Clock Troubles

    I use lite pipe cables throughout as well. I'm not sure that I have any at 18m, so can't comment, but I suppose it is a possibility. But to be clear, there's no "daisy chaining" issue with the litepipes, correct? So a distance problem on one machine should not propogate throughout the studio. I'm answering this one on the fly, but I presume that you have multiple ADAT pairs coming into your "master" 9652 where audio is being recorded? I use RME cards too so I can somewhat visualize how this could work... but again, I don't "think" I'd start with the lite pipes as the problem source. But, for what it's worth, I opted to introduce a litepipe patchbay (Frontier Apache) namely to simplify the cabling lengths that would otherwise have been required.

    All said, the key is finding the root cause so what about starting with your master device/machine, and reconnect one machine at a time, try using litepipe cables as-is and shorter just to remove that variable and continue to daisy chain the BNCs until the fault occurs- build it back out one daisy chained box (word clock) at at time until you find the spot where the symptoms begin to occur. I'm going to place my bets on this being related to the word clock daisy chaining vs. the litepipes.

  5. #5

    Re: Word Clock Troubles

    Maybe I can help a little. First off, a tech person with an oscilliscope would be really smart as he could absolutely trace your WC and terrminations. But if not here are some thoughts. Daisy chaining is considered a last resort transmission of WC, because if one of your units is doing something funky to the WC then the rest get it too. If you are to daisy chain then the way that worked for me was to use a "T" connector (I think these come in 75 ohm too) at each WC in with the termination at the last "T" connector.
    The "Proper" way to distribute WC is to have have each slave get it's own source from the generator either through the multiple WC outs or thru a WC distributor (Ardsync makes one but it isn't cheap). This way each unit is getting prestine WC.
    Your WC cablelengths are fine (I think the AES spec is 300ft.AND 75 ohm wires are imperative), but your adat cables are beyond spec. I can't remember but I think it' around 10 feet (although that doesn't mean they won't work).
    Another think to look for is if you have a WC loop going on somewhere (feeding the WC back into the adat lines- back into whatever is feeding WC) etc).
    hope this helps some.

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