Digital Processor Reviews

No history of the computer-audio marketplace could be complete without some mention of High Resolution Technologies, the California company whose Music Streamer was, in 2009, the first perfectionist-quality USB digital-to-analog converter to sell for as little as $99. One could argue that HRT's entire business model has contributed to shaping our attitudes toward the hobby: Because digital-audio technology continues to evolve at such a rapid pace, HRT has introduced a succession of newer and ever more effective Music Streamers, occasionally to the obsolescence of their predecessors; yet because those products have all been so affordable—remarkably and laudably so, given their thoroughly American provenance—we tend not to mind.

On the contrary, the arrival of each new Music Streamer is cause for celebration by those of us who want to know: How much more performance—and for how small a price—can we have today? HRT's answer for 2013 is their new Music Streamer HD ($449.95), which promises also to keep pace with the industry's growing library of high-resolution downloads.

Description
The Music Streamer HD is built into a lightweight aluminum extrusion 5.5" long and 3.5" wide, with plastic endcaps molded to suggest the same texture as the case's finish. One end is devoted to analog connections, with RCA jacks for single-ended signals, and a pair of XLR sockets for people whose systems can accept fully balanced signals: one of the new DAC's calling cards. The other end is home to a USB type B input jack, a bee-stinger–sized switch for selecting from USB 2.0 to 1.0, for those with older computers, and two groupings of indicator lights: a six-light bank for the common sampling rates from 44.1 to 192kHz, and three lights indicating 16 bits, 24 bits, and mute.

Like the Music Streamers II and II+, which I reviewed in the December 2010 issue, the Music Streamer HD is built on a single printed-circuit board, held in place by ribbing inside the case; the HD's roomier chassis, compared to that of its predecessors, seems necessary only inasmuch as its XLR sockets require a larger mounting area than RCAs. Analog output circuitry occupies the end of the PCB nearest the line-level audio jacks, while place of honor at the center of the board is given to a Burr-Brown PCM1794—a 24-bit/192kHz processor with its own 8x-oversampling digital filter—with current-to-voltage conversion handled by a differential stage outside the D/A chip. An XMOS microcontroller, supplemented with a Winbond flash memory, handles USB communications: The Music Streamer HD is an asynchronous device, using proprietary software written for that purpose by designer Kevin Halverson.

Also in common with Music Streamers past, the HD omits an outboard power supply, depending instead on the kindness of the USB bus and the voltage available thereby. Here the HD enlists the help of a CUI integrated DC-to-DC converter, which converts 5V DC into separate positive and negative swings, thus making a total of 10V available for distribution throughout the board.

Installation and setup
These days I expect few difficulties installing computer-audio products, in which regard the Music Streamer HD proved blessedly unexceptional. With the HRT connected to my Apple iMac by means of an AudioQuest Carbon USB cable, I simply clicked on System Preferences, then Sound, noting from the latter that the HRT identified itself as, simply, "USB 2.0 Audio Out." Throughout the review period, my computer never failed to detect and correctly identify the Music Streamer HD.

Because my Shindo Masseto preamplifier isn't designed for balanced sources, I relied mostly on the Music Streamer HD's single-ended outputs. Those jacks are installed quite close to one another—about 0.56" apart, measured on-center—but there was enough room for two RCA plugs of reasonable bulk. That said, I noted that the HD's jacks were mounted on the softish plastic endcaps rather less than rigidly, and thus were not immune to wiggling when I used bulky plugs and cables.

During the review period I had the good fortune to receive an integrated amplifier designed for fully balanced throughput—the new and very interesting Ayre Acoustics AX-5—thus providing the chance to try the HD's solidly nice XLR sockets; I used a 1m pair of Nordost Tyr interconnects I'd borrowed a while back, to review Ayre's own QB9 processor. (Before dropping entirely the subject of Ayre Acoustics, I'll mention also that their otherwise useful Myrtle Block isolation devices did not come into play during this review: Like most relatively inexpensive USB DACs, the Music Streamer HD seemed too light in weight to benefit from the use of those or other such things. I contented myself with keeping the review sample on a small pinewood table.)

Two final setup notes: Following USB connection to my computer, the Music Streamer HD became slightly—almost imperceptibly—warm to the touch, though not as warm as earlier HRT DACs. (I would imagine that this, too, is a function of the HD's roomier chassis.) And throughout my time with the HD, regardless of the music file being played, the processor's 24-bit indicator remained illuminated, its 16-bit indicator dark, even when I played a 16-bit file. (The Mute light at the bottom of the same bank of indicators could be toggled on and off with my iMac's F10 key—which did effectively mute and reactivate the HD.)

Listening
After a break-in period during which the Music Streamer HD suffered the indignity of supplying party music—highlights included some of the weaker selections by my heroes Ian and Sylvia, along with about three quarters of Sinead O'Connor's Am I Not Your Girl? (the three-quarter mark signaling the very end of my patience with that recording's extravagantly hokey instrumentation)—the new HRT processor went to work in my reference system.