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Since the dX-USB HD runs the XMOS USB transceiver, it's copasetic with Audirvana's integer/direct mode. The Cypress Semiconductor USB module of the Metrum Hex isn't. Prior the Hex had sounded its very best not with Audirvana 2.4 but PureMusic 1.88a set to 176.4kHz NOS. With the SOtM I could throw integer/direct into my personal Hex mix. But here I'd merely compare 176.4kHz USB direct to external USB bridge connected AES/EBU via very cost-effective Van den Hul 110Ω Pro cable. That incidentally works a real treat with my Cambridge Audio iD100 digital-direct dock and 160GB fully AIFF-loaded iPod Classic!

Metrum Hex receiving SOtM signal and feeding a Concert Fidelity CF-080XLS hybrid tube preamp

First up was the simple well-recorded Reflections of Palestine album by bouzouki player Ramzi Aburedwan. I wanted to focus on leading-edge clarity as the speed and incisiveness of plucked strings, the crispness and immediacy of hand-drum and shaker attacks and the peculiar reediness of the accordeon. I figured if anything I'd be tracking improvements in timing. This I expected should translate foremost to higher transient fidelity. Ditto for my second choice, bassist Randy Tico's earthdance with Jorge Strunz on guitar and the track "Caravan of Dreams".

Battery one active | 176kHz incoming data under external power

In either case the SOtM detour—an apt descriptor with the additional digital cable and expense involved—really did have higher perspicacity. That term's very makeup of spicy consonants (say it out loud) already fits. Be it marimba clacks, hissy air action of transverse flute, wiry snarls of electric bass, glassiness of bouzouki strings, fury of guitar rasguedo *... the beginnings of notes were defter. Think of unruly hair not slicked back with gel but spiked up. Such a punk coif emphasizes stiff pointy peaks standing out. The same spikiness when applied to musical micro shock waves means slightly greater dynamic expressiveness mostly on the very small signal level. But it had an unexpected side effect, seemingly making for higher macro action in the bass too. I don't believe that was actually factual—surely S/N ratio was unchanged—but it seemed real as though created by higher rise times or slightly quicker suddenness.
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* Click here for an Adam del Monte YouTube presentation of basic rasguedo techniques.


Returning to Metrum direct, this effect mellowed a bit as though our punk had his gel spikes clipped a bit shorter. Despite its NOS nature the Hex is far from soft. One of its greatest strengths in fact is transient prickliness. It peels out attacks from their 'soggier' surroundings. It thus came as surprise that this particular quality could be further honed. To be sure, this was nothing like a day'n'night difference. It was merely an added dose of leading-edge paprika. It didn't affect the complex sonic core flavor. It just created a bit more heat. (As an aside, the culinary tie-in collapses once we consider how with food heat occurs on the tail end after one swallows whilst this type of musical heat happens at the very start.)

The provided white umbilical is long enough to spread the two units as far apart as a conventionally sized component.

By now I knew what to focus on. Even so something highly elegiac, languorous and bel canto like the first track of the Tarkovsky Quartet's Francois Couturier album [ECM] made identifying the same quality far harder. From amongst piano, accordeon, cello and saxophone I only really noted it faintly with the woodwind. Here the difference was rather less pronounced. Would ambient recovery be another worthy focal point? Time to reach for m.a. with their always superior natural minimalist-recorded acoustics by way of Sera Una Noche and its saucy "Valse en mi" number.


Unexpected given the Couturier disc, I immediately spotted a difference for the clarinet. Rather than feeling more aware of its spatial interactions—reflections, connective-tissue air, performer halo—I heard the acoustic contributions folded back into the blackwood's primary timbre. The man now had bigger wetter tone. This was a harmonic thing and to me most apparent on the instrument I'd played since the age of 6 and later studied formally at the conservatory. Obviously it impacted all players. My spider sense for timbre simply works overtime only for the clarinet and its various saxophone relatives. Their sound and exactly how it's made is in my bones. If you play an instrument you'll have the same 6th sense about it.

ModWright KWA100SE, AudioSolutions Rhapsody 200

Cueing up "Wind" from Øystein Sevåg's Caravan—spacious synth pedals, lyrical piano, soaring sax, meandering bass, broadly panned drums—the latter's heavily accented cracking grew more emphatic. Here my ALO-Audio rewired Audez'e planar-magnetic LCD-2 cans on Bakoon's AMP-11R in hi-gain mode fronted by Burson's Conductor as D/A converter eclipse my primary speaker system. With the LCD-2's stunning bass, Bakoon's unbelievable speed, Burson's tone density and elimination of all room interactions, uncut immediacy is higher and so are contrasts. Where things now moved a notch closer to that was in the percussive violence which counterpoints the new-age spacey backdrop so brilliantly (think Michael Shrieve's famous Transfer Station Blue). Slightly greater definition or impact again benefited the electric bass too as though each of its centipede feet left behind a somewhat deeper imprint. Sevåg's piano notes also blossomed a bit differently.


In order of audibility, I'd rate SOtM's three advantages as transient articulation followed by tone (harmonic envelope) and finally impressions related to stage depth. Compared to Cees Ruijtenberg's excellent component-powered Cypress-based OEM USB, the first of these qualities was most apparent on well-recorded transient-intense material. Guitar, piano and snotty trumpet—open or muted—were good examples. In terms of magnitude these were just a few percentage points. On gravitas the other two qualities receded yet further. Much depended on recording quality and the amount of attention which audible space had received from the studio engineers. As reader Ted Brady wrote, don't expect obviousness on every recording. The SOtM twins can't recover something from nothing.


At this level of the game it's about narrow victories. Slices get thinner and thinner. Given past exploits amongst which the battery-powered Audiophilleo 2 ranked highest, SOtM's best two-box answer with SuperClock upgrade does push the envelope. Perhaps that implies it's the current chart topper and crème de la crème of this category? You'd have to know them all to be sure. Be mindful also that over USB direct you'll need another quality digital cable preferably of the AES/EBU sort; and another spare power outlet.


On coin, call it $1.500 to be plug'n'go with SOtM's best. Many complete DACs cost less. Obviously this 'go-for-broke' solution demands appropriate hardware context before it becomes any sensible straight-faced reco. There really are many other things you ought to do first. That's nothing but standard boiler plate. It's true for everything once a system has matured to no longer include weak links or suffer gross room perturbations.

In such a context upgrading a good amp to an even better one ought to net decisively bigger improvements than today's kit. But $7.500+ converters exist which coast on built-in USB-powered $60 OEM modules. Those types get flagged down hard by SOtM's best. Even in the context of Metrum's brilliant <€3.000 converter with optional USB installed, highly percussive rhythmically scintillating fare like Flamenco shows off what the dX-USB HD/mBPS-d2s combo does so very very well. The core benefit of higher time-domain fidelity at least to my ears is plain. Excitement! Music's encoded energy releases itself more vigorously. And that makes for more exciting auditions. So you might just have to opt in. If your current super DAC predates USB or excludes it by design—Ten Audio's TAD-1 comes to mind— this is an equally super way to add it.


Obviously we no more can hear time than we see empty space or air. Even so our sense of hearing is highly sensitive to timing errors. That's true even if we key in only on their effects and remain oblivious of true cause. Here this compact gear from South Korea plays to our innate sensitivity by reducing these common but subliminal errors. I think we ought to compliment the engineers at Soul Of the Music for advancing the state of the art in this still emerging sector. They also deserve kudos for making their offering a 3-step affair to allow us entry in financial stages; and for keeping the final total to something which for a SOTA effort does remain very fair. Those who prefer an integrated solution—batteries, super clock and USB transceiver all inside the main converter box—may consider SOtM's DAC or DAC/preamp. In fact given the impressive outcome of today's assignment, I'll put myself on the list for the latter once it becomes available...
SOtM website