Mini Post: What is the Digital Clock in My Audio Device For?

Get those clocks sync'd up!

All this talk about digital cables in the last post brings to mind the idea of a digital device "clock". What is it and why do we need to care about it?

You may notice that digital pieces of gear ask you about a “clock source” or “clock sync”. Unlike analog gear, which works with a continuous signal, digital works with discrete signals.

Think about this like you would think about the difference between a light dimmer and a light switch. With a dimmer, you can vary the amount of light from “on” to “off” smoothly. If someone told you to turn the light to 50% brightness you could smoothly move the switch to the half-way point. With a light switch, you can only be on or off. There are only two “states”. If someone asked you to get to 50% brightness using a light switch, you would need to cycle the switch on/off very quickly to approximate the level of brightness halfway between the and on and off positions.

OK. I know you want to try it but you'd have to do it much quicker than even your sweep-picking, finger-tapping, legato-shredding fingers could do it. Something like 120 times per second. Fine. Go ahead and try. I'll wait.

This is how digital signals work. They are constantly toggling the output between on and off very quickly to approximate an analog signal. A digital audio device may do this toggling something like 44,100 times per second (44.1kHz). How does it know that it's doing it the right number of times? It has an internal “clock” (based on pretty much the same technology an actual digital clock would be based on) to help it get this number and timing right.

Now imagine you have two pieces of digital gear. One has an output that is doing this on/off toggling very quickly and to the schedule provided by its internal clock. The second piece of gear has an input and is also checking to receive a signal 44,100 times per second but it’s using its own clock to keep its own schedule.

It’s possible that the two clocks are not in sync with each other and that the piece of gear that’s checking the signal is not checking at the exact right time so it’s only catching some of the on/off signals that are coming through. This is a problem and would lead to audible clicks and pops. This is a Lord of the Flies situation. The way we get around this problem is to nominate strong leadership. Tell the devices which one of them is the leader and have all of them use the leader's clock.

If you hear audible clicks an pops and you have multiple pieces of digital gear in your chain, this is one of the first things to check.

Remember to check out calmfrogrecording.com for a FREE test mix that's yours to do with as you please.

Cheers and happy recording!

Vadim