Music in the Round #76

In my last column, in the November 2015 issue, I talked about Marantz's AV8802A preamplifier-processor and two accessories: UpTone Audio's USB Regen, and a DIY battery supply for my DAC. This month's column is all about accessories, and for me that's unusual. Some items, like interconnects and speaker cables, are usually considered accessories because they're not fundamental components (eg, source, amplifier, speaker), even though they're essential to getting any sound at all.

As far as I'm concerned, an accessory is something without which your system would still work just fine. By definition, accessories are preferential, not essential: You buy them in the hope that they'll improve the sound of your system, or make it easier or more convenient to use.

Back in analog days, I could decide whether a different tonearm counterweight was a good idea because my undergraduate study of physics had covered the mechanics of mass, compliance, and frequency. I could also wrestle with the electromagnetics of transformers and motors. At the time, digital signal processes were still mostly theoretical.

Today, I'm losing ground. While I grasp more than a bit of how music is digitally encoded and decoded, I find it difficult to understand how different data-transmission methods (USB, HDMI, Ethernet, FireWire, etc.) affect the quality of the analog output signal and, ultimately, listening enjoyment.

Consider such products as the AudioQuest JitterBug and UpTone's USB Regen. Many people, whether skilled or naãve, biased or impartial, have attempted to test such gadgets, but I'm not aware of anyone who has demonstrated a link between variables in data transmission—beyond basic hardware specs—and what we can actually hear. Of the correlations we do see between hardware/software variables and the condition of a product's output signal—measurements that can reveal either improvements or deteriorations in signal quality—most changes are so slight as to be considered below the level of audibility, amounting no change at all. (Of course, in all such cases, one can question whether relevant parameters were being tested.)

On the other hand, some manufacturers offer products accompanied by a technical description and a statement of goals for that product—but without test-bench specs. "Try it!" they say, and offer return privileges. Hope and expectation play big roles in deciding whether to add an audio accessory, choosing the particular one(s), and determining whether they're worth the cost and bother. Expectation bias is a friend to such vendors, regardless of whether the product makes an essential difference or is a placebo.

Is there hope? I think so. First, several websites are hosting ongoing, apparently candid, and often contentious public discussions of the testing and measuring of data-transmission accessories. When the smoke clears, this give-and-take can have led only to better understanding of these technologies. Limited by my technical competence, I am a fly on the wall, but it's fun to watch the sparks fly.

As for the "Try it!" approach, that works, too. Most of us have a closet stuffed with old accessories that didn't stand the test of time. I've bought many gadgets, hoping they would improve the sound of my system by at least one audible increment, but most I've tossed aside. Some made no difference from the get-go. Others offered an initial flush of excitement, but the effect faded over the ensuing months. Few accessories have lasted long in my system: As audio technology advances, the worthwhile improvements effected by today's accessories are sometimes incorporated into tomorrow's new primary components.

These days, I might try an accessory because of word-of-mouth, so long as it doesn't cost the sky. Despite my general skepticism of tweaks and accessories, I'm as much subject to expectation bias as the next guy. I'll just tell you what I hear; as for the rest, I'll wait for the dust to settle.

AudioQuest JitterBug USB filter
John Atkinson and the crew at AudioStream.com (footnote 1) have already scrutinized this little gadget ($49), and everyone seems to like it. How could I not give it a try? I was particularly interested in using it in my weekend system in Connecticut, in which resides my already overachieving miniDSP U-DAC8 multichannel USB DAC: Getting eight channels of USB D/A for $299 is amazing—and budget-priced products always seem ripe for tweaking. And, as I reported last time, UpTone's USB Regen—a USB signal regenerator intended to isolate audio peripherals from computer-system noise—had made a hugely satisfying improvement in that system's sound: Surely, the miniDSP would be a suitable mate for the bruited 'Bug.

When I asked AudioQuest for one, they sent two: AQ recommends using two—and no more—JitterBugs on each USB bus. I searched the JitterBug's box, and AQ's detailed instructions about how to use JitterBugs with various USB-connected devices, for any information about precisely what it does, and how. I found only two relevant statements:

"JitterBug is designed to remove unwanted noise currents and parasitic resonances from both the data (communication) and Vbus (power) lines of USB ports. . . .

"JitterBug's dual-circuitry measurably reduces unwanted noise currents and parasitic resonances. It also reduces jitter and packet errors (in some cases, packet errors are completely eliminated)."

Well, that's admirable—but how? JA was unable to find, in his measurements, any difference in DAC output resulting from the insertion of a JitterBug. Others have reported the same—but some have seen a change in the digital signal's "eye pattern," as observed on a digital oscilloscope. An eye pattern is a way of representing the precision of the digital pulses, which ideally should be square, thus indicating that the on-off transition is perfectly defined in time. Apparently, the JitterBug applies some kind of filter so that the squarewaves' risetime is slightly increased—the opposite of what we want if we want to reduce jitter. However, while we assume this is not good in the digital domain, it's unclear what effect such a filter might have on the DAC's analog output. Is it possible that the JitterBug is actually doing something else, and that the apparent digital compromise is merely a side effect? As long as it's reasonably square, is the eye pattern even relevant?

I don't know. But I, like others, can hear the JitterBug's positive effects on the analog output. I connected one 'Bug between the output of my server and the input of the miniDSP U-DAC8, and—with or without the UpTone USB Regen connected—the JitterBug did seem to sweeten the treble. And when I removed the JitterBug, I missed it. Though the JitterBug's effects were more noticeable without the USB Regen in the system, they were smaller than those of the UpTone accessory—which not only sweetened the treble but also, with multichannel recordings, tightened up the integration of elements within the soundstage.



Footnote 1: See the reviews by Michael Lavorgna and Steven Plaskin, respectively, here and here.
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