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Will a Composite Video D/A work for Wordclock?

Discussion in 'Pro Audio Equipment' started by Randyman..., Aug 9, 2003.

  1. Randyman...

    Randyman... Well-Known Member

    Hello all,

    I am looking at getting an Apogee Rosetta (or simular), and I am also wanting this to serve as my "Master Word Clock" via the 75 Ohm BNC connections.

    I will need to distribute this signal to 3 or more devices, so I will need a Distribution Amplifier. Will a good Broadcast quality 75 Ohm composite video D/A work?

    If not, what are some reasonable alternatives. I have seen the Drawmer Master Clock, and it looks VERY nice and flexible with SRC and all, but a bit much $$$.

    FYI - I will be using this with a Roland VS-2480, a TC DB-Max, and the Rosetta converter. I want to allow future expansion to 6-8 units utilizing wordclock.

    Thanks for your help... :cool:
  2. RecorderMan

    RecorderMan Distinguished Member

    you can get by without a distribution amp for now.
    Rosetta into roland into tc.
  3. Randyman...

    Randyman... Well-Known Member

    Well, I actually have (2) of the TC DB-Max's, and I will use both of them as Analog-to-Digital converters when tracking, and with the Rosetta (total of 6 channels) through a Roland AE-7000 R-Bus to AES/EBU converter (which also has Wordclock inputs).

    That makes for one master (Rosetta), and 4 slaves (VS-2480, AE-7000, two DB-Max), and I want room to expand. I will still have a Toslink, a Coax, and another AES input I will not be using, but I will want a word clock avalible for anything I will plug into these inputs.

    I know I can get around with sync'ing to the SPDIF or AES signals, but I want to go with the Wordclock route for less jitter, and I want to get this set up where I can add more digital gear without buying more interfaces and clocks...

    I would think that Composite Video has a much higher bandwidth than a wordclock, and any phase drift would cause chroma shift in the video, so broadcast video D/A's should be pretty rock solid, and I can get them CHEAP! I just don't want to get one, and find out my clock is drifting all over the place.

    Thanks again! :cool:
  4. RecorderMan

    RecorderMan Distinguished Member

    ahh..well that's a different story. start searchinf for the best cheapest wc distro......

    p.s. next time give the full scoop, it's quicker :c:

    P.P.S btw to clarify...I'm talking about a strictly work clock distribution amplifier when I said distro...I don't know all the brands, but something like the one that ardvark makes (they kinda started this stuff) maybe check there's out then compare from thier for price/performance.
  5. Opus2000

    Opus2000 Well-Known Member

    I'm not so sure a video distro box is what you want to look for. You may think that it might have a tighter clock source on it but in the long run it may not.

    Video clocks are typically very common to drift after long periods of time. I know this after having helped make sure the Apogee Big Ben was solid...we compared it to an aardsync and a couple of other video distro boxes and they all drifted in the clock after a good amount of time.

    Also remember that using the Rosetta to feed a D/A distro box will cause propagation delay which can cause some clocking anomolies in the long run.

    You can get by without having to use a distribution box. Here's what you can do:

    Get some BNC T connectors. Place them on all of the Word Clock inputs of the other devices. Take the clock output of the Rosetta and put it to the first device with the T connector, on the oppposite side of the T connector send that to the next device in the chain and continue this on till you get to the last device in the chain. At that point you will put a BNC termintor(75 Ohm) cap on the open end of the last BNC T connector and you know have all devices receiving the clock at the same time!

    This way there is no propogation delay when you go in and out(or daisy chaining) of each device!

    If you need any help at all making a decision, give us a call at Apogee. You may want to look into the Apogee Big Ben..you'd be amazed at how that can make your gear sound even better! It's hard to make some people believe it..so you should just see about getting one to try out. There's going to be a review of it in the October Mix Mag.

  6. Randyman...

    Randyman... Well-Known Member


    I thought if a device did not have a selectable "Termination", it would default with the 75 Ohm termination turned "ON". Neither the VS-2480 or TC DB-Max have "Termination off" or "on", so I would assume they are already terminated at 75 Ohms, correct?

    If that is the case, wouldn't this lower the overall termination impedance in the chain?

    This is EXACTLY how we do it at our TV station and "Black Reference", but the destination units have a defeatable "75 ohm termination" which are defeated in this case and terminated with a 75 Ohm BNC plug at the end of the chain. We still use black D/A's since we have well OVER 200 peices of audio and video gear all sync'ed together, and automated!

    I will look into the Big Ben, but all I will really need is the D/A to distribute the Rosetta's rock-solid clock (Once I get it!)...

    You guys rock! Thanks for all the info :cool:
  7. realdynamix

    realdynamix Well-Known Member

    :D Ok Opus, when can we expect a high quality multi-output wordclock DA from Apogee? Enough out's to feed an entire facility, self termination regulation and warnings, self adjusting for signal losses and frequency variations (RC).

    Special cable to reject stray spiking misinterpreted as data, and able to drive long lines with delays less then a few Ps. The device can have added features for house clocking originating RS232, self adjusting, as well as countdown timers, system clock updating and other goodies. Anything in the works?

    Randy! Tell me about your system on the a/v/f forum. Sounds like a cool place.


  8. Opus2000

    Opus2000 Well-Known Member


    Audio and Video are a little different in terms of sync. Video needs the sync reference in terms of drop frames and black burst.

    Audio needs timing reference of sample rate only.

    A D/A sync box would only give you propogation delay when using it with the Rosetta.

    Rick..Big Ben has virtually no jitter. Allows you to sync to video and redistribute that out 6 word clock output. Both output 5 and 6 can be configured for any type of output in terms of sample rate divisions or multiplications.

    Big Ben can also do pull up/pull down as well as VSO mode.

    Believe me, if you are going to need a master clock box this is the one to get.

    Big Ben can also tell you if the source you are feeding from each output if it is terminated or even over terminated!

    In conlusion Randy, most audio gear is not self terminating. Some do have it and some don't.

    You should check each device to see if indeed it is self terminated by putting a meter to it and see if you get 75Ohms on the word clock input. If not then it needs to be terminated.

  9. RecorderMan

    RecorderMan Distinguished Member

    Great tip opus! off to the DMM.
  10. Randyman...

    Randyman... Well-Known Member

    Just to clarify...for my sake...

    If the units are terminated with an internal 75 ohm resistor, then hooking up multiple terminated units via "Daisy Chaining" to one clock would reduce the net impedance, correct?

    If this is true, I would NOT want to run the units in a "Daisy Chain" config, or the termination impedance will be way less than 75 ohms net.

    I see what you are saying about the D/A and propogation delay. The Rosetta will be perfectly "In Time" with itself, but the D/A will offset the wordclock, and therefore offset the Rosetta's AES signal to the VS-2480, since the 2480 is locked through the offset word clock. Correct?

    This would only affect the Rosetta, not the other gear, but enough of a reason to rule this out.

    Alright, I will start investigating master clocks. I know I will want the most expensive one I can find, but just say I want an "Intermidiate" model. I just need a solid master clock, and a 1x6 or 1x8 D/A on BNC connections. The SRC is cool, but I can do without for now, as all of my stuff is 44.1K. Anyone heard of the "Smart Clock"? Runs about $300, and will sync BNC x6, AES, and SPDIF. I would like to spend around $500 or so.

    Thanks for the input :cool:
  11. Opus2000

    Opus2000 Well-Known Member


    Yes, it will affect the Rosetta only in an off sort of way...the Rosetta will actually be the only device in time. All the other devices may have an offset of the clock timing which can cause you much grief in the terms of troubleshooting!!!!

    As an Apogee tech I've gone over this several times with people and most of the time they end up doing what we suggest due to the fact that you are not going to be double terminating the input!

    You are essentially terminating the cable and not the device! It's like SCSI hard drives...you have to terminate the cable on the last device! get it!!

    Also you need a D/D sync box if anything as you can't feed sync from a D/A box?!!! :D
  12. Randyman...

    Randyman... Well-Known Member

    Much thanks, Opus.
    You da-man

    Later :cool:
  13. Randyman...

    Randyman... Well-Known Member

    Anyone tried the Lucid GENx6 or the GENx6-96? They are a generator and 1x6 D/A for around $400, or $550 for the 96K model.

    $1500 for an Ardvark or Apogee is just a bit much for me to spend on my project studio for now. I plan on spending $1500 - $2000 on my monitors, and I think they will make much more difference in my mixes than a $1500 clock. Choices, choices.

    Any others I should look into in the $500 range with 6 BNC outs?

    Thanks again :cool:
  14. Roly

    Roly Guest

    Swissonic makes a word clock generator/distributor. It sounds fine to me but I have nothing to compare it to. I bought it direct from Swissonic. It was a demo piece used at trade shows and was very affordable. 600 CDN I think.
    There's a link at the Swissonic site for demo sales. Also bought 2 AD96 MKII 4 channel AD converters which cost me 800 CDN each. I like em but again have no means of comparison.
    cheers Roly

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