HD = DXD/DSD
Way back when I reviewed the Resonessence Labs Concero (see review), I wondered/wished, "I wonder if they could easily add DSD capabilities to the Concero?" Depending on your definition of "easy", the answer is a resounding yes. It did take a new DAC chip but ESS came to the rescue and the little Concero now has two siblings; the HD with its DXD/DSD capabilities and the HP which adds a headphone amp to the HD. Like the original Concero, the HD in addition to functioning as a Coax S/PDIF and USB DXD/DSD DAC, it can also operate as a USB to S/PDIF converter handling up to 64x DSD since 128x DSD is beyond the S/PDIF specifications according to Resonessence Labs.
The Bel Canto uLink asynchronous USB-S/PDIF Converter works the same as most other like-devices taking the USB output from your computer and turning it into S/PDIF data your DAC can connect to but it adds an interesting wrinkle to the proposition by including a glass ST Fiber output. The interesting thing about an ST Fiber connection beyond its inherent immunity to electro-mechanical noise is length—you can run an ST Fiber connection over 100 meters.
The V-Link192 should appeal to anyone that wants to play up to 24/192 music files from their computer who own a DAC that does not have a USB input. It should also appeal to those people who have a DAC that does not support 192kHz files via USB but does support them via Coax or XLR, and even for those with an older adaptive USB DAC that does not have an asynchronous USB input. Out of these three options, the first two are, imo, no brainers whereas the efficacy of the last will be based on a case by case basis.
Getting High (definition) Without Wires
The Audioengine D2 DAC is one of a new and few breed of wireless DACs capable of sending, receiving, and playing high definition music up to 24-bit/96kHz. As a matter of fact, I know of no other wireless DAC that'll do the same, today. Of course there are loads of UPnP streamers out there that include wireless capabilities but I'm talking about just-a-DAC with 24/96 wireless capabilities built-in (i.e. no dongle needed). One basic difference is wireless DACs are file format agnostic whereas streamers are not. They're more picky. And most streamers piggyback on your existing wi-fi network whereas the D2 provides its own.
A computer is not optimized for the uninterrupted streaming of audio data. It has rapidly become established wisdom, therefore, that the optimal means of extracting audio data from a computer's USB port is to operate that port in what is called "asynchronous isochronous" mode. This lets the receiving device, such as a digital-to-analog converter (DAC), control the flow of data from the PC. In theory, asynchronous USB operation (not to be confused with the asynchronous sample-rate conversion used in some DACs) reduces jitter to unmeasurable levels, depending on the accuracy of the receiver's fixed-frequency oscillator, which is used to clock the data to the DAC. By contrast, in the alternative and almost ubiquitous USB operating mode, called "adaptive isochronous," while the sample rate of the output data, averaged over a longish period, will indeed be the specified 44.1 or 48kHz, there will be short-term fluctuations, or jitter, due to the oscillator having to change its frequency every millisecond to match the uncertain rate of data flow from the PC.
The weekly Vote! Page is one of the most popular features of the Stereophile website, and the August 22 question, "Should Stereophile review more or fewer computer-audio products?", generated a record number of responses. No less than 88% of those responding asked for more coverage of products that allow a computer to be a legitimate source of music in a high-end context. Just 7% of readers wanted less coverage.
As someone who wrestled endlessly with the nine-pin serial ports and the RS-232 protocol with which early PCs came fitted (footnote 1), I welcomed the Universal Serial Bus (USB) interface when I first encountered it a decade ago, on the original Apple iMac. Plug it in. Don't worry. Be happy. The computer peripherals work as they should, which was often not the case with RS-232. It was a given, therefore, that the then-new USB port would be seen as a natural means of exporting audio data from a PC (footnote 2), but the first generation of USB-connected audio devices offered disappointing performance.
The speed with which audiophiles have adopted a computer of some sort as their primary source of recorded music might be thought breathtaking. But with the ubiquitous Apple iPod painlessly persuading people to get used to the idea of storing their music libraries on computer hard drives, the next logical step was to access those libraries in listening rooms as well as on the move. A few months back, I wrote a basic guide to the various strategies for getting the best sound from a computer: "Music Served: Extracting Music from your PC." Since then, Minnesota manufacturer Bel Canto Design has released a product that aims to simplify matters even further.