Understanding Digital Music Systems

Music servers and computer audio
Understanding Digital Music Systems

Many music lovers considering the leap to a digital music system find the new technology intimidating. Terminology is inconsistent; architectures for complete systems are amorphous; configuration options are bewildering; obsolescence is always a threat.

Though procrastination might seem prudent, the potential benefits are enticing. Digital systems allow you to store a large music collection in a box no larger than a CD player. Cataloging software makes it easy to find recordings, and control software makes it possible to play them without leaving the comfort of your sofa. Storage capabilities also provide convenient safekeeping for music downloads. Support for HD audio promises a listening experience superior to that of CDs and LPs. The potential rewards are great, but the risk of an inauspicious purchase is real.

This article attempts to lower anxiety by confronting the bugbears. I will present the architecture of a complete digital system and show how products from different categories map onto different subsets of this architecture. Using this mechanism, I will define a set of terms that unambiguously describes components in a digital music system. I will also respond to questions frequently asked by newcomers. After reading this article, I hope you will feel more confident as you embark on your quest for a modern audio system.

The Terminology Problem
Much of the confusion surrounding digital music systems results from inconsistent terminology. Different manufacturers use different terms to describe components that do essentially the same thing. A device that plays a digital recording might be called a network player, a music player, a digital audio player, a media server, a music server, a streamer, or a media renderer. Part of the explanation for this hash of terminology is poor choices by the developers of related technical standards; part is the desire of manufacturers to differentiate their products; and part is simply the haphazard way in which language evolves.

The terminology for analog music systems does not suffer from these problems. Use the words “amplifier,” “integrated amplifier,” “preamplifier,” “tuner,” “receiver,” or “loudspeaker” in the right company, and no one will misunderstand you. Moreover, most people in this group implicitly understand how those components map onto a block diagram of an analog music system (Fig. 1). Through long use, these terms are widely understood to refer to one thing. A power amplifier, for example, takes a small signal at its input and transforms it to a big signal at its output no matter which company manufactures the product. Manufacturers differentiate their power amplifiers by characteristics such as the class of the output stage (A, AB, B, or D), whether they use tubes or transistors, or the appearance of the casework, but users can always count on connecting a line-level signal to the input and loudspeakers to the output.

Digital systems are more amorphous. The binary numbers that comprise the digital representation of an audio signal are robust. You can transfer them through cables, optical fiber, metal traces, or air. You can store them on hard-disk drives, DRAM, solid-state drives, or flash drives. You can subject them to electromagnetic interference, ground loops, or transmission-line effects. You can perform mathematical operations that make it possible to pack more of them in a given amount of storage. None of this matters as long as the numbers you started with are the ones that ultimately arrive at the destination.

Numbers are numbers no matter what they represent, so digital systems are able to use elements to carry a variety of signals. The same internal buses that carry digital audio at one moment carry control signals or unrelated data at others. A USB interface can be used to communicate with a mouse, a keyboard, a monitor, a network interface, a hard-disk drive, a DAC, and much more. Analog systems do nothing comparable because the purpose of an analog interface is defined by the function of the device it is attached to, not by an abstract description encoded in numbers.

Finally, the function of digital circuits is determined in large part by software, not just by the interconnection of electronic components. Software is easy to change because it too is composed of numbers. The same hardware can perform radically different functions simply by altering the software. For these reasons, digital systems are much more pliable than analog systems are.