Zeroes & Ones
Simply, the numerical representation of a slice of audio frozen in time could be either above or below a threshold. There are just two choices: on or off. The resulting one-bit audio would sound like a nasty guitar fuzz box.
Greater precision in measurement leads to more faithful reproduction of the sound we wish to preserve. We could choose to record sound as a stream of numbers using our familiar decimal system, based on our 10 fingers.
But digital electronic circuits are much more comfortable with the binary system of counting, where instead of 10 different levels there are only two, represented by zero and one.
The string of numbers flip by like the frames of a cartoon to create the illusion of a continuously variable analog of the original sound. The faster the pictures flip by every second and the better the picture quality the more realistic the illusion of movement in the cartoon, and so it is in audio, where a higher sampling rate and longer word length results in better quality digital audio.
When we put up a microphone and create an audio signal chain between the natural sound and what comes out the other end, we are putting our faith in the equipment manufacturers.
Just as we have a palette of choices in creating that signal chain, manufacturers have a broad palette of components to choose from when creating the piece of equipment that we choose to run our sound through.
While the equipment designer is picking just the right resistor, capacitor, or digital signal processor, he has to keep in mind a slew of constraints placed on him, such as reliability, end cost to the customer, support, appearance, and so on.
Regardless of using resistors (analog) or chips (digital), the designer still has a slew of constraints of which to be aware.
So a lot of the talent a designer brings to a product is the ability to make the right balance of compromises to deliver a cost-effective solution for the customer. And this is what makes one product or technology a better choice than another. So where do they go right and what are the traps?
Playing The Numbers
More is better, right? In our society, we tend to be impressed by bigger numbers. If 16-bit audio sounds better than 8-bit audio, then 24-bit audio must sound even better.
Manufacturers wow us with science. They tell us that their analog to digital converters have 24-bit performance.
A simple engineering rule of thumb says that we get about 6 dB of signal-to-noise improvement with every bit we add. This means that 24-bit audio has a dynamic range of six times 24, or 144 dB.
Yet when we read the specs, we’re lucky to see 118 dB out of a so-called 24-bit converter. So the difference between the claim of 24 and the reality of not even 20 is called “marketing bits.” They are in there to make you and I believe we are getting something more.
Dynamic range is just one measure of performance. Other measurements, such as distortion, similarly fall short of the claimed number of bits.