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Auditioning Clocks (gulp!)

Discussion in 'Pro Audio Equipment' started by anonymous, Jun 8, 2002.

  1. anonymous

    anonymous Guests

    Hi Steve, Bill, RM, and all passers-by!

    Maybe you can help me with this one. So far in my lifetime I've managed to carefully avoid participation in clock comparison tests, mostly out of fear that my badly abused ears wouldn't be to hear any difference anyway.

    But with the imminent arrival of an HD system, i am faced with the choice of using the internal PT clock (rumored to be much improved), my Lucid Genx6-96, or my Cranesong HEDD as the master.

    If you have any opinions, they would be welcome, but assuming that I would "want" to do my own test I have a couple of dumb questions:

    DUMB QUESTION #1: In comparing the three, do I want to record the same piece of audio three times (once with each clock) or is it sufficient merely to apply the three clocks just to the playback of a given piece of audio?

    DUMB QUESTION #2: What, in you opinion, makes the "best" kind of audio source material for exposing differences in clock quality, i.e.: loud vs. soft, simple vs. complex, test tones, single monophonic instruments, reverb tails, widely panned stereo stuff, etc.

    Any thoughts on this subject would be welcome. Feel free to ridicule the dumbass questioner as well!
     
  2. audiowkstation

    audiowkstation Active Member

    With any test that can be performed, you also have subjectivity VS objectivity. Said test involves many appraoches.

    I use an acoustic recording of a Concert grand Piano for critical anaylisis, because it is a percussive instrument and has Micro and Macro dynamics galore, plus a wide frequency range and it is a natural instrument VS an elecronically produced one. (No one knows how a synthesizer really sounds)

    Here are some approaches that may serve you well:

    Of the tests decribed, you will have to divide them into six catagories. Make a spreadsheet and compile scratchpad anaylisis for further review. As a professional equipment reviewer, this is a way to do it. Also see http://www.enjoythemusic.com and look through the equipment reviews and grid coluum for more understanding...like the points system.

    Catagories:

    Short term vibe.
    This is a quick first impression, can prove to be accurate.

    Blindfold test.

    Here, you have another participant administering the playback, without your knowledge of playback device.

    Long term analysis.

    This includes all your notes and using the points system.

    Input and output cross relation.

    Here, you will use device a (producing) with device A/B/C (reproducing)
    Then Device B (producing) with Device A/B/C (reproducing)
    And finally Device C (producing) with device A/B/C (reproducing).

    Next you employ translation. (How the device transmits the test results to real world applications). Input and output cross relation needs to be also tested here.

    For 5th, you look at the value, ease of setup, user friendliness, instructions and other associated gear to make the machine of choice work it's best. If a 1000.00 Piece performs 3% better than a 100.00 piece...the 1000.00 piece loses.

    6th, you must compare the results with at least a panel of 3 others and average the results to keep favortism to a minimum. Above testing should take approx. 2 months.

    This is a brief on evaluation. Hopefully from these terribly simple guidlines, you can establish a test to get to the heart of the matter which way you can use the equipment in question at it's maximum potential. Once you find the results you are looking for, then writing a review of those results (if you think the final anaylisis means anything to others) for all to learn from. Any good acoustic recording will work well, the Piano and the Human Voice are really hard to beat.
     
  3. anonymous

    anonymous Guests

    Great answer, Bill. Thanks.

    The other thing that adds to the difficulty is unless I pull everything out of it's rack, I've got to crawl around and make connections between each test, making it harder to do qucik comparisons. I may be forced to unrack everything just to be able to listen in a timely fashion. What a pain!

    Maybe I'll get lucky and someone will do their own clock test and post the results, saving me the trouble! :D
     
  4. knightfly

    knightfly Active Member

    Bill, thank you for that dead on method. I think only someone like yourself who has actually done such reviews and tests would have been able to elucidate each point so clearly. I have yet to reach the point of having to do such a test, and features may win out over absolute performance when I do. I am working toward including audio for video in the next incarnation of my studio, and the only box I've found that does video sync very well is the Nanosyncs by Rosendahl. It was recommended to me by Greg Malcangi some months ago, and since then I've checked their specs out. It is spec'ed as tight as any other I've seen, and is a lot more flexible than most.

    LD, in the price range you're talking about, the message I get from those who've been there is that in most cases the PLL jitter you get from externally syncing usually overshadows any minute decrease in clock jitter from the external clock. In other words, say you have a converter that has 7 picoseconds jitter worst case, and an external clock that has 5 picoseconds jitter - when you use the PLL circuitry in the converter to lock to the external clock, you might introduce another 4 picoseconds of jitter, for a total of 9, not 5 ! This is just part of why the series of tests outlined by Bill would be necessary if you really want the absolute best sound quality you can squeeze out of the gear you have. And yes, you would probably have to un-rack the suspects in question. I would also recommend listening both on your monitors and with headphones as part of the test, to help rule out any room anomalies. (Yeah, Bill, I know you said it was a brief list, sorry...)

    "Maybe I'll get lucky and someone will do their own clock test and post the results, saving me the trouble!"

    Or, you could just buy a Nanosyncs because that red motif just looks SO damn kewl... Steve
     
  5. stedel

    stedel Guest

    Hi there folks. Wotcha littledog!
    Lucky you've got a nice piano in your studio, because accoustic instruments, percusion, stringed and/or the human voice are good test scources for detecting the bane of a non "decently clocked" system - namely jitter.
    There are also times when it is prudent and wise not to use the internal clock provided by your DAW (no matter hw rock solid it may be).
    So you need something like the Nanosync anyway (well I know I do).
    In terms of the constant "patching" that needs to be done, this is not as bad as you'd think. Once you have your digital inputs, devices (reverb eg), video etc. clocked appropriately it should run pretty smoothly, coherently, and conveniently for you, requiring minimum re-patching. That is if your DAW of choice is a cool system, and the Tools HD system is definately an improvement (so I'm told and read). Look forward to hearing of you unpacking your new Tools!!!

    Just remember - coherent, well defined and nicely sensual stereo sound field, with all the depth that erudite littledogs enjoy!!!!

    Kind regards
    :cool:
     
  6. sdevino

    sdevino Active Member

    The HD system uses an internal PLL so using an external clock will not change the performance of the digitizer or a/d clock.

    So if you are looking to compare the performance of the 192 0r 96 i/o using internal or external clock, you should not see any difference.

    This is because the clock that ultimately runs the a/d or d/a is regenerated inside the box via a PLL.
    The PLL locking mechanism will filter out any external clock jitter because its loop bandwidth will not be high enough to see it.

    So bottom line is you can do your test if you want to compare another converter to the HD converter, but using different clock sources for the converters on the HD is really pretty pointless.
     
  7. anonymous

    anonymous Guests

    So, Steve, would you recommend using the PT clock as the master, and using the Lucid just to distribute the clock? Or use the Lucid clock as the master, which won't affect PT if I undersatand what you are saying, but might make a difference to the Cranesong HEDD, etc.
     
  8. sdevino

    sdevino Active Member

    You need to supply a really accurate clock to anything with a converter in it (A/D or DAC).

    So you can go either way. I doubt if there is much difference between the 192 and the Lucid clock in terms of quality. I would suspect that since the Lucid clock is designed for distribution, it will handle cable loads a little better. Simplest setup is probably having the 192 feed the Lucid and have the Lucid distribute clock to everything else. This way at least PT is always setup with internal clock (just a convenience advantage IMO).
     
  9. RecorderMan

    RecorderMan Distinguished Member

    Use the HD as the clock and use the head for what it does. Sell the lucid and buy some more mic's, pre's, compressors, ect.
     
  10. bluemt

    bluemt Guest

    I'd avoid the hype if I were you and use the HD clock. I bet it works well.
     
  11. Jim Chapdelaine

    Jim Chapdelaine Active Member

    LD,
    A good clock setup will improve your sound in a noticeable way.
    After shopping around extensively I ended up with this.
    I generate word clock from an Apogeee 8000SE and send that to an Aardvark Sync/DA distributor.
    It sends clean word clock via matched length 75ohm cable to a 2nd 8000SE, a tc system 6000, a Digi 192
    digital interface, my board and occasionally (embarassed look - a BRC if needed)
    everything is always locked and word clock is more stable than AES. There are other master clocks out there that work great but my little system works fine and sounds great.
    Also, the Apogees easily slave to video for post and scoring work in which case I keep the same setup but slave the first 8000 to black burst and send that to the video device.
     
  12. audiowkstation

    audiowkstation Active Member

    I bet that does work nicely!! thank you for sharing!

    The lowly(SIC) BRC has a real rock solid clock..don't be embarrased!!!!
     

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