Digital audio networks promise a system where audio is routed so that every channel is available everywhere in the network, without the limitations on the direction of signal flow, or even the system’s physical connection topology.
A signal can be injected anywhere in the network, be perfectly preserved as it travels through the network, and then output anywhere: on the network.
Simple, right? Well, at least in concept.
Every technology evolves because every technology has inherent challenges to overcome. Thomas Edison was probably not thinking about rumble when he was inventing the phonograph; he turned the crank, sound came out of the horn, and the party started.
Tape-based recorders had challenges with noise, bandwidth, dynamic range, and wow and flutter, but over time these challenges were addressed by technology improvements, and tape transport became the basis for capturing the sounds of our industry for decades.
Then audio went digital, and the same evolutionary process began anew, and now digital technologies are beginning to replace analog systems in a wide range of applications.
Today we are in the midst of this same type of technological evolution for audio transport. At first, the only way to move a signal was with a copper wire.
More recently, point-to-point digital transport was introduced with clear benefits (more channels on less expensive cables, freedom from ground bops, theoretically loss-less splits, and so on).
Soon, perhaps inspired by what was happening in the computer industry, systems that could “network” an audio signal from point to point to point were developed.
But this technology is still evolving. As an industry, we’ve certainly achieved a lot – we can move a lot of audio a long way over inexpensive cables. But digital audio networks (DANs) still face disadvantages that lead many to choose analog solutions (if they didn’t, we’d see digital networks everywhere).
The real promise of a DAN is to merge the best attributes of analog and digital audio connectivity and combine them with the advantages of a network without introducing unpleasant trade-offs. The audio would have the fidelity and simplicity of the best analog systems and the power and flexibility of digital. That’s where the next generation of DANs needs to take us.
ANALOG VS. DIGITAL POINT-TO-POINT CONNECTIVITY
To understand the challenges associated with networking a digital signal, let’s start with some of the basics of digitizing audio.
A/D – D/A Conversion: By definition, a digital signal is an approximation of the original sound – all sound is analog. Thus, the analog-to-digital (A/D) and digital-to-analog (D/A) conversion processes are critical to achieving a high fidelity digital signal.
Fidelity of the conversions is affected by bit depth, sample rate, and clock integrity. Generally speaking, the higher the bit depth and sample rate, the more accurate the digital approximation of the analog signal.
But increasing the bit depth and the sample rate increases the amount of data for each channel, and every given cable has a finite and fixed amount of bandwidth which can be filled with 1s and 0s. So on a basic level, fidelity and channel count are at odds with one another (see High Fidelity A/D Conversion sidebar).
The other issue is dock integrity. Remember that a digitized signal is not simply a serial stream of Is and us. Those 1s and 0s are associated with a particular point in time, which is governed by the clock.
To get perfect fidelity requires a perfect clock, but perfect clocks are a theoretical ideal where all clock transitions occur at their theoretically ideal time; in reality all digital audio docks suffer from some amount of jitter, or variation.
Too much jitter affects the audio quality and can make the audio sound harsh. And as we’ll see, dock integrity is one of the most fundamental challenges in networking a digital signal (see the Jitter and Wander sidebar).
One other important consideration in the A/D-D/A conversion process is latency. It takes time to convert an analog signal to digital, and it takes additional time to re-convert the digital signal back to analog.
