Can anyone explain the importance of a A/D interface Clock

Wayne Franco · From: silverdale, WA. USA

I really don't understand some of this stuff yet. I know a guy who records a lot who says one of the most important part of digital recording is a jitter free clock. What does that mean?

Thanks for your replys

Wayne Franco

Rick Hedges · From: Oregon, USA

Digital recording takes "snapshots" (i.e., samples) of the audio waveform many tens of thousands of times a second. In order to get the best sound, you want those samples taken and played back at evenly spaced intervals in time. For example, if you recorded one sample every second, you would want the playback to also space those samples one second apart. If you played the first sample, waited five seconds before playing the second sample, waited half a second before playing the third sample, etc., the original sound would be altered. Those timing variations are a form of jitter.

The clock regulates the time interval between samples. This is typically done by running a current through a special type of crystal that oscillates at a predictable, stable rate. A/D and D/A converters are very complex, and while a good clock is important, so are many, many other factors. Generally, if you have decent converters, the clock in the thing is probably not the weak link. If you're connecting multiple digital devices, you're generally better off running every device off the same clock. Check out the recording forum "pro sound web" for a lot more info on this subject...

Rick Hedges

Wayne Franco · From: silverdale, WA. USA

So, say the sample rate is 44.1 hz that is the sample rate per second. Everything should be syncing at the same time during that sample period. If not than the sound you are getting back is no as good as it could be. I just looked on the pro recording forum. Searched A/D clock, A/D timing. I guess I'm not even sure what question to ask.

Well, in the mean time I have asked a few more questions and found there are outboard "clocks" that can make your A/D converter signifently better by using this device with it. Gee...all it takes is money!

Rick Hedges · From: Oregon, USA

You generally don't need to worry about the clock. If you have decent converters, the internal clock will almost always result in less jitter than connecting an expensive external clock. On the other hand, if you have multiple outboard converters that you are using simultaneously to record to a single source (for example), then you need to make sure the different converters are getting their clock signal from a master clock. I'm guessing you don't fall into that category, though. There are usually a host of other more important issues to worry about than minute clock discrepancies.

Ben Strano · From: Nashville

I never ever, ever worry about outboard clocks. When I go to a studio that has outboard clock I always ask to use the converters internal clocks. I can't tell you the problems I have run into because the assistant didn't make sure that the session sample rate and the outboard clock were the same. MONSTER headaches. Clocks add maybe 1% to your sound.

Other things that add to your sound:

Player - 50%
Instrument - 20%
Microphone - 5%
Mic Pre - 5%
Compressors and other outboard gear - 8%
Digital Converter - 1%

I always think it is best to spend your money where you get the most bang for your buck.

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