How you get to the finish line matters

In Ted Smith's latest 5 minute video Jitter and Clocks he made a quick comment that may have just passed some of you by without notice. "Jitter doesn't matter until right at the point where you convert it to analog." Let's examine that comment today. When you download a track of music from a site like Blue Coast Records, for example, that file is fed to your from a computer in northern California, over the internet, through your home's router, into your computer in a very circuitous and torturous path indeed. Because this downloaded data doesn't have a clock tagging along there's no chance for jitter, but once you play it out of your computer over USB or S/PDIF you add a clock and our dear friend Mr. Jitter is back. But it doesn't matter how jittered the data itself is until the very last moment. Until the moment you try and couple a clock to its data going into whatever IC or circuit you're using to convert that data to something we can hear. What this means is that you can have something as a source of digital audio, like an iPod, Sonos or computer that is full of jitter. And the amount of that jitter doesn't actually matter until you try and do something about converting that data to audio. So let's imagine the iPod has 200ps of jitter and the Sonos has 10 times that amount (it doesn't, but we're just picking on it). The data in the two are the same. There will be no difference in how either sounds or performs until the point you actually convert the data to analog. Now, you might say "so what? I don't care about anything other than how it sounds and I can't hear digital audio, so when we decode the two examples and listen, the Sonos will sound 10 times worse than the iPod. And if I use a bad cable to connect the devices to my DAC, it'll be even worse. I get it. What's your point?" Here's my point. If you manage to resynchronize the musical data and the clock so the jitter reaching the DAC is reduced to identical amounts, then regardless of how jittered the two sources started out, they will sound the same. This has great implications if you think about it. It's the whole idea behind the original Digital Lens we created in the 1990's, and home to claims that many manufacturer's make about no jitter getting into their converters. But HOW you accomplish this feat of jitter reduction is critical. And therein lies the rub. More tomorrow.