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What is jitter?

What is jitter?

Digital audio is full of wonderful words, initialisms and acronyms: wordlength, LSB, ADAT… For a quick little FAQ today we try to answer the question “what is jitter?”

When you’re reading the specifications of a digital audio interface, such as the new Focusrite Saffire Pro 26, you may have come across phrases such as  “quality digital conversion and JetPLL™ jitter-elimination technology ensure pristine audio quality…”

What is jitter? by ApogeeFrom this statement, you can guess that jitter is a bad thing, something that we want to reduce. And we do. If you read our post on how digital audio works, you’ll remember that the sound is converted into a digital signal by taking regular ‘samples’ – converting the sound into a sequence of numbers.

What is jitter? – Good times, bad times

The thing with turning your audio into samples though, is that each one of those samples is supposed to be taken with exactly the same amount of time between them. The samples are taken at times dictated by a clock. If that clock drifts, then the samples will end up with different amounts of time between them, distorting the original sound.

There is an excellent set of diagrams on Apogee’s site that show this beautifully. Given their experience in making converters and interfaces, Apogee are – as you would expect – a good authority on the subject!

If you look at the image above, this is how the samples should be arranged along a sine wave. With a perfect clock, the samples are all an equal distance apart. If that clock was irregular, imagine the image if you stretched it. That perfect sine wave would distort all over the place.

That’s not the sort of distortion that you want.

So, with modern, high-quality audio interfaces, all the time and effort that goes into designing a good converter pays off with a digital signal that’s a great representation of what you put into it. Even if you’re then going to distort it through your favourite overdrive plugin, you want to be starting with the right raw materials!

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