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I just got a clock generator. can someone explain to me what the differents between super clock (256x) and word clock output? are they the same thing?


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knightfly Thu, 04/04/2002 - 22:23

JT, Superclock is definitely NOT the same as Word Clock. Word clock is a stream of pulses (not sure if they're symmetrical or rectangular) which are the same frequency as the sample rate being used. Superclock is a term coined by Digidesign, for use with protools and some other Digidesign hardware, and I believe it is 256 times the rate of standard Word clock - I have no Digidesign products in my studio, so haven't delved very deeply into this part. I guess the idea of Superclock was that a higher frequency clock would give greater accuracy of timing and improve the sound of the AD/DA converters by minimising clock jitter.

Some newer digital hardware, even though it can run at high sample rates (96k, for example) still wants to see standard rate (48k) Word Clock at its external Clock input (Tascam DM-24, for example) and the Mixtreme PCI card put out by Soundscape can only run up to 48k when synced internally, but it will accept external Superclock and run at 96 K if set up right. These are just two examples; the point is to read the manual for each device and make sure you're giving each one exactly what it needs to operate correctly.

If you're running an external clock generator and it has multiple outputs, the main thing is to keep the number of devices on each output to a minimum by distributing them evenly. Use as short a cables as possible, especially if using BNC connectors, and ONLY use 75 ohm VIDEO cable, NOT 50-ohm ham radio or ethernet cable. I'm assuming because you already have a clock generator that you know that every piece of digital audio gear in your studio must be clocked to the same clock source, whatever that is, or you'll get random clicks and pops in your sound. (Not talking down, I've just found that it's best to mention any points I think of which could be important and let people ignore what they already know.)

Hope that answered your question, sorry I don't know more about Superclock other than it is different. If you're wanting to use a Superclock output, some devices (Aardsync, Nanosync, ?) allow you to change the configuration of their outputs between WC, Superclock, WCx2, etc - Check your manual for this if that was the reason for your question... Steve

knightfly Fri, 04/05/2002 - 07:28

Right, JT - EVERYTHING that is digital (as opposed to analog, not like "digital readout") MUST be recieving its Word Clock signal from the same source (clock generator, for example) and that source must be at the sample rate being used for the project - so, if you're doing a 48k sample rate project, then all pieces of digital gear must be set to that. Bit depth (16 bit, 20 bit, 24 bit, etc) isn't QUITE as critical, only because almost all digital gear will truncate (drop) any extra bits it cannot use. A 16 bit processor with a SPDIF digital input can be fed a 24 bit signal, and it will just ignore the 8 least significant bits. HOWEVER, you probably won't like the result - using the dithering options in ProTools will accomplish the same thing with better results.

JT, you need to understand that I know maybe 5% more about ProTools than your average housewife, never having used it. My studio is a project studio not for hire at the moment, and being on a less-than-unlimited budget, I tend to go for more cost-effective solutions. Since my last answer, I did go to Digidesign's site and check into clock briefly - it looks like they still use Superclock on their hardware, except for the new HD systems, which it doesn't sound like you're involved with. Also, if you go to the support page and search on "superclock", you'll get a couple of basic ideas on their Word Clocking. Superclock is, indeed, 256 X as fast as "base" clock (44.1 or 48k) Here is a link to their site - click on products and follow links to system diagrams; note that 256 clock is mentioned as going to their converters.

If you want real, "been there, done that" info, post your questions in the Daw World side of this forum, under Pro Tools. The guys there use the stuff every day and can get you going in less time than it took to read this.

Guest Fri, 04/05/2002 - 17:17

Knightfly basically nailed it. The thing to remember is that ProTools interfaces, like the 888/24 require superclock, regardless of what sample rate you are recording at. Almost everything else uses regular word. For instance, I have the newer Lucid Genx6. It has 6 outputs that can be individually configured to superclock or word clock. I have one output set to superclock, which is sent to the 888/24's, the rest are regular word clock and go to things like a Cranesong HEDD and TC Finalizer. On the front panel you can choose the sample rate (44.1, 48, 88.2, 96). Whichever one you choose will be the same for all the outputs, both superclock and regular clock - since everything must be on the same sample rate regardless of what kind of clock format it uses. It is important that the devices receiving the clock all be set to receive the appropriate sample rate as well. Sometimes that means selecting an "external sync" option, as choosing a numerical sample rate may force the device to ignore the incoming clock and to run off it's own internal clock. That could result in pops and clicks.

Hope I didn't make a confusing topic more confusing. Speaking of confusion, you'd be surprised how many people thing word clock is somehow related to SMPTE or MTC.

knightfly Mon, 04/08/2002 - 01:58

JT, you're welcome - best of luck with the PT project.

LD, thanx for the vote of confidence - I would have moved JT's post if it were on my turf, but you managed to find it anyway. "Speaking of confusion, you'd be surprised how many people thing word clock is somehow related to SMPTE or MTC." - Egad, you mean they're not???!? :=)

Guest Thu, 04/25/2002 - 14:10

Vlad, quickest way to attract knightfly's attention is to post in the room where he is a moderator (Tech).

But if you want the best answers to clock questions, ask Greg M. over in the DAW World area.

But a quick and probably inaccurate overview:

All digital devices operate at a specific sampling rates. These rates reflect resolution: how many times per second a "snapshot" of the audio waveform is being taken. Think of it is one second of audio being cut into 44,100 slices, Kind of like dots per inch resolution on a printer - the more dots/higher the resolution, the more closely the digital image will come to resemble the original analog waveform.

In audio, the usual lowest sampling rate is 44,100 per second, for reasons that have to do with if the sampling frequency isn't at least double the highest frequencies one can hear, artifacts are introduced into the audio. (See "Nyquist Theorem" for more info).

But back to clocks, since the timing of 44,100 or 48,000 or 88,200 or 96,000 or more "slices" per second is obviously extremely small increments, it is important that one very accurate clock be a master timer for all the digital devices being utilized. If each device is left to it's own internal clock, there will be audible pops or clicks as different devices drift out of sync.

I'm not much of a tech person, so this may not be a totally correct explaination. But the jist of it is probably ok. See Greg over in DAW world for the real scoop!

knightfly Thu, 04/25/2002 - 14:57

Hey, LD - You know how "sensitive" I am; how dare you intimate I'm so narrow-minded that I only hang out on my own forum? (hehehe)

Vlad, If you don't get help from Greg, hang on for a couple of days - I'm up to my ass in 'Gators at the moment, and this could take a while. Til I get back, consider whether you're willing to spend about $80 on two books, and actually read them - If so, cool - if not, I'll have to look harder for some links I saved. Be aware that serious understanding of this subject is going to involve some study, but it's do-able, and as LittleDog pointed out, necessary for proper operation of any digital studio with more than just a sound card.

BTW, LittleDog, that was about as concise and accurate as anyone could ask for, and depending on Vlad's thirst for knowledge, could be all that's needed.

Vlad, if you see this before I get back, think about how deep you want to go - be back soon... Steve