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A/D converters

— By Paul McGowan —
We're releasing a brand new product this month, the NuWave Phono Converter. It's an analog phono stage and an A/D converter together in one package. I have received a number of questions about A/D converters, RIAA curves, what it means and how they work. I thought first I'd do a small series on A/D converters and later we'll delve into the RIAA curve, its history, what it does and why it exists. If you've ever listened to digital audio anything, you've listened to music processed through an A/D converter. The name simply stands for Analog To Digital Converter. Simple enough. It is the opposite of the D/A converter which stands for Digital to Analog converter. A/D, D/A. Start with analog, end with analog and in the middle of the process you have nothing but a bunch of 1's and 0's that you have to keep track of. Maybe first let's look at those 1's and 0's because there are a few of us misguided as to what that really means. I wouldn't want you to think there's actually a "1" and a "0" because these are numbers and digital audio has no actual numbers, only representations of numbers. When we refer to 1 or 0 we really mean ON or OFF and even that's not as simple as it sounds because we're also concerned with the transitions from ON to OFF, the timing between each of these changing states etc. In prior posts we've covered a lot of ground explaining timing, on and off states, jitter and all the technical mumbo jumbo associated with digital audio. What's important to remember in this series is that we will be talking about a numeric based system that uses a type of code to represent the numbers. Think of an abacus like the one pictured here from Ikea. Abacus Each of the beads on this abacus REPRESENT a number but are not an actual number. In fact, they are just a bead. The combination of these beads, the space where there are no beads and their arrangement form numbers that are understandable to those who know the code. Think of each bead as an ON state in digital audio and the space where no bead exists as the OFF state. In this same way, we can represent numbers in the code digital audio uses, called PCM or Pulse Code Modulation. All you really have to remember about PCM is that it is a numeric based code, with combinations of ONS and OFFS in groups - each group represents a single number - each group is known as a word - each word a single sample of the music (like a snapshot). It's a big abacus. Tomorrow we'll dig a little deeper.

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