What's a word clock?

[karambos]

I apologise in advance for my ignorance but what does a "Word Clock" actually do?

 

I'm told this is a good one.

 

But I don't know what it does?

[Rog]

It's a big topic!

 

Word clocks provide one clock signal to all your other gear so your whole studio is reading off the same page, so to speak.

 

This minimises jitter, jitter is where the clock signal isn't as clean as it should be so samples don't get dealt with evenly and regularly. Instead some get through slightly before or ahead of the point in time when they should get through. This degrades the sound.

 

That's it in a nutshell.

[Michelle ggurl]

That's a very good description, Rog. I've heard Apogee is good, as is Lucid. I don't use wordclock because my recording interface doesn't support it, and I don't use digitally synced outboard gear. If it was supported on my system, that's how I'd sync up external (ie, better) D/A and A/D converters.

[boosh]

another cool clock

[Philip OKeefe]

EVERY digital audio device must have a word clock. That clock can be internal (inside / built into the device) or via an external "master clock".

 

When you have only one digital device, you can use the internal clock. That clock is what determines how fast the sample rate flows along. Digital audio has a sample rate - such as 44.1 or 96 KHz. What that means is that samples - slices, "samples" or "snapshots" of the audio waveforms - roll past at a rate of 44,100 (or 96,000 or whatever) samples per second.

 

When you connect two or more digital audio devices, it's important that they are both being clocked to a common clock source. You can set things up so that one device acts as the clock source (the "master clock") for itself as well as the "slaved" device. This is important because you want the start and ends of those samples to be in sync with each other - otherwise you'll get clicks, pops and even dropouts as you're trying to digitally route audio from one device to the other.

 

Instead of using the internal clock on one of the digital audio devices, you can use a master word clock generator for ALL of the digital audio devices in the system. The advantage is that everything is controlled from one central clock source. Also, the stability and accuracy of these external clocks is usually better than the onboard clocks in most units, thus improving the sound quality - Better clocking means less jitter, better stereo imaging and usually "tighter" bass and / or less "smearing" of the high frequencies.

 

You've probably seen me (and Craig, and others) rant about the lack of BNC word clock I/O's on a lot of digital audio devices. IMO, they should be on EVERYTHING - it makes connections to a master word clock generator MUCH easier. However, if your device lacks such connectors, all may not be lost - S/PDIF and ADAT lightpipe both carry word clock data on the same cable that carries the digital audio, and depending on your setup and what you have gear-wise, you can usually clock something else to the master clock and then "daisy chain" the word clock data from that device and out to the S/PDIF or lightpipe equipped device and clock it that way.

 

For example, my Lucid word clock generator feeds word clock via a BNC cable into my Yamaha digital mixer. My Digi 002 lacks a BNC word clock input ( ) but it does have a S/PDIF in and a ADAT lightpipe in... so by running a S/PDIF or lightpipe cable from the Yamaha to the Digi 002, and setting the 002 to slave to incoming word clock from that cable (instead of running from its internal clock) I am able to get everything locked up.

 

One thing I should mention - word clock is NOT time code! If you really want to lock things up, you can use word clock to get the sample rates locked together, and MTC (MIDI TIME CODE) for positional sync or trigger sync. MTC commands from one device (such as a standalone digital hard disk recorder) are sent out to the second device (such as your computer DAW) and tells that device where it is positionally (bar #1, beat #1, etc.) and when they get to the correct position, both devices will start playing. It's then the word clock that keeps them playing at precisely the same speed - thus preventing any "drift" over time.

 

Bottom line - you need to have EVERY digitally connected device getting word clock data from only one source.

 

It's a complicated subject, and I might not have explained everything in a perfect way, but there's a ton of discussions on the topic here on the forums. Search DF's forum, as well as GM's forum archives for more information.

[spokenward]

Phil (or Mike or anyone), the mlan stuff pipes the wordclock on their bus. Did you have enough time to form an opinion on that aspect of the system during your test? I am thinking especially of the imaging and soundstage. If it works well, that might be one of the better arguments for the system.

[Philip OKeefe]

I didn't have any problems with routing word clock via mLAN at all. Ditto for the audio and MIDI data - mLAN cables carry all three at once; which is a tremendous advantage - no more cable spagetti!

 

As far as the quality of the clocks, it seemed quite solid. However, I imagine it's just a matter of time until we start seeing dedicated master word clock generators with mLAN jacks on them.

[jpmiii]

If your looking for a good treatise on the subject then may I suggest Mastering Audio by Bob Katz