This feature article originally appeared in the June/July 2019 issue of WiFi HiFi Magazine.
The acronym D-A-C is turning up with increasing frequency in audio circles. But it's time to ask ourselves: do consumers even know what a ‘DAC' is, or why they should buy one? Even in the trade, do we truly understand how DACs work, and what makes one better than another?
Of course, we all know that DAC stands for ‘digital-to-analog-converter.' But do we understand how a DAC work its magic, really? What limits the quality of a DAC's output? If we don't understand these devices, we're not going to have much luck explaining them to customers or recommending the right ones for their needs.
So let's step back for a moment and consider the DAC: crack open the black-anodized chassis, and see what's really in there.
The term ‘DAC' is open to misinterpretation. It can refer to the raw chips that do the actual work. Or it can apply to audio products that include those chips. Adding to the confusion, it can also be used in conjunction with other audio terms, as with DAC/amps or DAC/streamers.
If we want to de-mystify the jargon, we have to start at the beginning. Where did all these DACs come from?
The first digital-to-analog converters necessarily accompanied the first digital audio formats. You can't pass a long stream of binary numbers to a speaker and expect to hear Mozart... or even Metallica. You have to convert the digital data back to an analog waveform.
"Basically, any digital device that makes sound includes a DAC," emphasizes Stephen Mejias, Director of Communications for AudioQuest. But people first encountered DACs without knowing it. When the first CD players rolled out in 1982, every one of them necessarily contained a DAC. But nobody talked about it, any more than they would about the transformer in a power supply.
Obviously, CDs represented a huge leap in sound quality. They were free of tape hiss, surface noise, static noise, turntable rumble, and so on. But early CD players were far from perfect. In particular, audiophiles quickly began to complain about shortcomings of their built-in DACs.
This led to the first appearance of discrete audio products called ‘DACs,' which attempted to provide superior decoding ability. Such ‘audiophile DACs' have continued to evolve and flourish, commanding price points up to many thousands of dollars.
The latest in the DragonFly Series of USB DAC + Preamp + Headphone Amps are the DragonFly Black and Red that can be used not only with computers, but also Apple and Android smartphones and tablets, transforming them into high-fidelity music players.
The average customer took no notice - especially since CD players continued to improve, to the point where an external DAC would provide minimal audible benefit to the average audio setup. So there was no broad demand for lower-cost DAC products - until it quietly arrived from an entirely different direction: the personal computer.
Audio came to the PC in stages. In the early 1990s, Creative Sound Blaster add-on cards started allowing desktop PCs to decode and encode CD-quality digital audio. By the mid-1990s, free software allowed digital audio to be compactly stored in Fraunhofer's lossy MP3 format.
Almost overnight, the Internet was awash in audio files. And all those files needed to be played - a task for which the PC was anything but ideal. "Those devices - laptops, smartphones, tablets, et cetera - are designed to perform many, many functions," observes Mejias. "Audio output is just one of them."
PC sound cards improved steadily, but they were up against an environment that was noisy both electrically and acoustically. And while Microsoft did push for development of a Multimedia PC (MPC), the resolutely general-purpose computer never became a proper audio device.
Similarly, when portable MP3 players exploded on the market, they were designed for compactness and storage capacity more than sound quality.
There were attempts to raise the bar. In the early 2000s, Pow Chu Moy published a DIY project for a tiny gadget that came to be known as a CMoy headphone amplifier. Even today, Amazon continues to list pre-built versions of this much-loved device, traditionally packaged in tiny metal Altoids boxes.
And portable DAC/amp devices also started to turn up. But it wasn't until 2012 that AudioQuest's DragonFly line started winning awards and drawing attention to this emerging product category. The DAC had truly arrived as a consumer product.
The BDA-3 External DAC from Bryston is fully DSD-enabled, offers PCM playback capable of 384kHz/32-bit resolution, has a multitude of inputs, from HDMI to USB, and a network module that facilitates control via TCP/IP and RS-232.
In our focus on individual products, we often forget about the enabling ecosystems, without which those products could never have existed. In the case of DAC/amps, the ecosystem was really brought to life in 2006 by the establishment of the USB Audio Class.
This spec defined a standard way for software to communicate with an outboard DAC/amp, via the ubiquitous USB port. The spec originally supported only up to 24-bit/96KHz audio, but Audio Class 2.0 quickly increased the capability to 24-bit/192KHz.
The USB Audio Class even includes a control protocol, which allows audio devices to respond to apps as if they were an integral part of the controlling device - PC, phone or whatever. It's a perfect example of how standards can create interoperability, and thereby facilitate the emergence of entire new product categories.
Today, there's a broad range of USB DAC/amps on the market, including both tiny portables and larger units with advanced capabilities. They allow users to get superior headphone sound, at a modest cost. A major boon, given that excellent headphones can be had for much less than speakers of similar audio quality. And, of course, headphones offer a controlled, optimal listening environment, which may be harder to achieve in the average home.
It's important not to forget the ‘amp' side, which has its own impact on sound quality. This is an area in which manufacturers can distinguish their own products. Most digital devices, ranging from smartphones to PCs, lack sufficient output to drive high-impedance audiophile headphones. Mejias notes that the DragonFly Red outputs up to 2.1V, which should handle them with ease.
In portable applications, power drain can be a consideration. Early portable DAC/amps put a heavy load on a smartphone, impacting battery endurance. But Mejias notes that lower-power DAC chips have largely solved that problem. He reports that AudioQuest is able to demo DragonFly units all day long at trade shows, and routinely sees 18-24 hours on a phone charge.
The most recent evolution of the DAC is in digital streaming devices. For example, the NAD C 658 BluOS Streaming DAC ($1,999) combines a simple computer that can inhale digital music from Internet streaming services; a DAC that can decode the music to analog; and a preamp that readies the output for an amplifier.
NAD says the C 658 is "redefining the architecture of hi-fi playback," and this seems to be true. With the rise of streaming, this type of device is likely to become the central component of the home audio system.
Combining a quality pre-amplifier, DAC, and BluOS streamer, the NAD C 658 includes BluOS, Bluetooth aptX HD, Dirac Live Room Correction, and Modular Design Construction that allows all major circuits to be upgraded and replaced as needed to future formats.
NAD throws in various other features that are desirable in today's audio systems: Bluetooth with aptX HD compression for wireless headphones; multi-zone support; Dirac Live room correction; and control options for most portable devices. And it makes the unit modular, so any new capabilities that come along can be added later.
Simplicity is key. "You don't need a computer; all the complexity has been put under the hood," says Greg Stidsen, Chief Technical Officer with Lenbrook International (owner of the NAD brand).
Of course, the DACs that are built into various products are bound to keep improving. Recent LG V-series ThinQ smartphones, such as the 5G-capable V50, are a notable example, making an improved "32-bit Hi-Fi Quad DAC" a major selling point.
Vincent Luke, Marketing Manager with iFi audio, acknowledges that in the highly competitive phone market, it makes sense for LG to "test the water" with an audiophile-grade DAC/amp, and offer audio that's "a cut above the rest."
But Richard Schramm, Owner of Parasound Products Inc., is skeptical. "They did it because they could," he suggests. "It's an itty-bitty tiny DAC. It doesn't cost them that much." Schramm questions if there's a huge demand for this kind of audio feature.
Of course, in a mobile product, it is debatable how much improvement in sound quality will actually be audible. However, if nothing else, the new LG phones should free users from any need to carry an outboard USB DAC/amp, while delivering comparable audio quality.
The G8 ThinQ smartphone is one of many from LG that includes a Quad 32bit DAC among its audio feature set. The V50 ThinQ, which is not yet available in Canada, boasts the same 32-bit hifi quad DAC, along with DTS:X 3D surround.
LG has been oddly reticent about the amp power of the new phones. But ESS press releases list the output as 2V rms, which should be enough to drive even high-impedance headphones. That would be an odd combo on the subway, to be sure. But we can perhaps imagine more-private listening situations where a portable music source with high audio quality would be worthwhile.
We can also envision future use cases that might be enabled by the existence of such pocket devices. The way we consume music continues to change.