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It turns out that the NOS DAC moniker requires splitting up into modern and vintage halves. This follows what I'd attempted previously for 300Bs. There Western Electric and Full Music SE marked the vintage aesthetic, contemporary Czech valves from EAT, Emission Labs and KR Audio plus the Chinese Synergy Hifi vendor the modern variants. CAD's converter belongs decisively to the vintage NOS DAC breed. In my scheme that's characterized by a hooded treble which mellows upper harmonics, shortens decays and diminishes transient dynamics. The overall sound is aspected by innate minor softness, an emphasis on the fluidic non-choppy elements of playback and a subtly voluptuous midband emphasis. In speaker terms think WLM Stella with its 2.5-inch Visaton paper-cone tweeter.
from John Darko's WLM Stella review

Metrum Hex, CAD 1543 & APL Hifi NWO-M converters with Audirvana+ 1.4.1 or PureMusic 1.88a software players

The modern NOS DAC aesthetic is embodied by Metrum's Hex which by comparison replaces the Visaton tweeter with a Raal ribbon as in my Aries Cerat Gladius speaker. This becomes noticeably more lit up in three distinct ways:
• Harmonically loaded transients like triangle and glockenspiel strikes are fierier with higher microdynamic cresting.
• Decay trails elongate.
• Audible space as a function of decaying reflections gets more illuminated.
One takeaway is that transient-intense fare peppered with string plucks, metallic hits, wooden cracks and such gets more piquant and rhythmically adroit just as Martin Colloms' quote of Metrum's smaller Octave predicted. The Hex intensifies this attack crystallization further to become a true high-order PRaT champ. What prevents this from turning front-heavy nervousness or temporal rigidity are high tone mass and extended decay trails. Relative to expectations for higher transient acuity from going NOS, the modern iteration conforms, the vintage one does not.

By contrast the CAD 1543 thus was softer on the attacks, darker on the decays, texturally and tonally minorly damped and consequently dimensionally less intensely sculpted. Unlike the pungent black Dutch coffee, the UK deck added milk and sugar like many Brits drink their tea with a post-colonial nod to Indian chai. To requote Scott Barry, his machine is aimed at audiophiles who don't like the sound produced by most digital sources. It's likely that his sizeable output transformers are deliberate contributors to the 1543's unhurried minorly rich presentation. To remain with the vintage/modern theme, think textile/paper drivers rather than metal/composite variants. Tonally the emphasis of such sound is on the meaty bloom portion. Spatially it's more focused on performer physicality than the airiness of surrounding space or the crackling electricity of rhythmic urgency.

The Bulgarian NWO-M split the delta between Hex and 1543 by omitting milk but not sugar in its coffee. It reintroduced the treble extension and energy the CAD had subtracted without matching the sterling transient speed and fiery leading-edge dynamics of the Dutch.

Though with hifi metronomic time is never altered, subjective time is surprisingly flexible. Some gear feels flush with rush, drive and adrenaline. Other kit feels more settled, stately, relaxed and at ease. The CAD deck belongs squarely to the latter class. Its primary concern is not with mega-pixel measurbation. It's more about the patience, grasshopper mandate of slowing down to smell the roses. On Anoushka Shankar's Anourag, the implicit bargain was about less sympathetic string glitter to obtain more sonority in trade. On Aytaç Doğan's Deva, the brushed and tickled cymbals seemed tuned lower, the embers fizzing off his tremolo'd qanun strings were lazier and shorter lived. Once the strangely retro disco groove kicked in, it was less snappy and more casual. The implicit trade was for wood over metal, hereness of body over thereness of space, density over startle factor.

If I'm allowed an educated guess, exorcising ultrasonic noise to an extreme degree seems part of Scott Barry's recipe. That would be true despite unfiltered aliasing artifacts in the band just above audibility. Regardless of exactly how unaddressed MHz+ noise interacts with its own circuitry and that of associated gear technically, its absence apparently translates as utter parallel absence of pixilation (unnatural sharpness). Sonically it makes for a real smoothie as though all subliminal on-edge-ness or nervousness had been bled out. On gestalt there's some overlap with certain bandwidth-limited valve gear whose output transformers act as their own noise filters. By fronting a completely in-the-dark system without any glowing bits, the CAD 1543 DAC thus manages to inject a similar feel and even on tone mimics it a bit with its meaty midband focus as the comparison with the tube-buffered NWO-M showed.

Vis-à-vis all other digital gear that came through my rig this year, the CAD converter certainly did sound different just as its designer promised. Whether it'll be your aural antidote to poisoning by digititis depends on whether you feel poisoned in the first place. Here health is no absolute standard but contingent on individual biases and expectations, what your ideal is and what you presently own. While I can't be certain, it seems a pretty safe bet that vinyl lovers who don't play in the uppermost strata would find a transition to the CAD quite seamless. I deliberately qualified this because by comparison to current standards the 1543 is limited on raw resolution and top-end extension. I thus disagree with The Ear's Jason Kennedy of it possibly being a "cat amongst the digital pigeons". My pigeon-slaying cat would require superiority on all fronts, not just a strategic re-weighting of qualities to achieve a certain undeniably pretty effect.

Final words. Beautifully built, excessively minimalist on functionality and very expensive, Computer Audio Design's maiden product is unique on numerous fronts. I don't believe there's anything quite like it currently to market. Hence should its particular combination of attributes push all your buttons, you won't be satisfied by anything else. The matte acrylic enclosure looks classy and liberates the inner circuitry from chassis field effects. A complete absence of switches means the machine is always on and purposefully does only USB. The sonics are utterly de-stressed, dark, moist, chewy and heavy on tone, flow and density. What they won't do is airiness, heightened pace, lit-up space, edge rimming and adrenaline speed. If the CAD 1543 were a speaker, it might be a vintage dual-concentric 15" Tannoy. As amp it might be an early Jeff Rowland or it could approach a present-day ARS Emitter II. As thermionic valve it'd be a vintage 300B, not a solid-plate EML 45 or 50.

It's a deliberate counter voicing to current hyper-rez tendencies. Whether that makes it the DAC which black licorice lovers going computer audio will embrace remains to be seen. If UK dealer/importer Walrus Systems is an indication, the 1543 has made inroads into that scene already. The conversion process to disc-less thus seems in motion. With CAD, hold-out PCfi fence-sitters could well get comfortably cushy and off their pointy posts. No offense intended but don't you think their ... well, arses would thank them for that? Streaming audio sounds so much better than you might have thought. That's what this is all about. Come on down!