I would love to read reactions to the “technology bits” here (WADAX streamer and DAC review from R Harley). I ll get one of these to listen to at my home soon, double blind of course and I can report back. But the claims in here seem bizarre to my non technical brain. I have been using fiber optic connection with my Roon streamer and I dont see how that can be bettered. Underlying is mine.
“The Reference Server project began four years ago when Wadax began testing its At-lantis Transport with disc-ripping features and dis-covered that the length and type of USB cable made a significant sonic difference. The sound changed even though the bits representing the audio signal were identical. Wadax also discovered that the software processing the audio made a difference, specifically the Linux compiler, and even the settings within a specific compiler. During this work, it also discovered other mechanisms by which bit-perfect datastreams were sonically compromised, including the influence of power supplies, grounding, and noise coupling.
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For starters, the Akasa optical interface provides complete gal-vanic isolation between the Server and DAC, meaning that there's no path for electrical noise. This galvanic isolation also means no noise modulation of the ground plane, no ground loops, and no noise crosstalk. Second, a signal traveling down an optical inter-face is subjected to less dispersion than a signal traveling down an electrical conductor. Dispersion is a phenomenon in which the energy of a signal is spread out in time—a contributor to the “bit waveform distortion” mentioned earlier. Think of a perfect square wave at the transmission end of a cable; at the receiving end the square wave's edges are rounded, and the rise time is slower, causing the leading edge of the square wave to become slightly slanted. The square wave's shape is altered because the cable's transmission speed isn't infinite. It's this leading edge of the square wave that represents a binary transition from one to zero, or from zero to one. If that edge is slanted, the precise tim-ing of that transition is indeterminate; it could occur at different points along the slope.
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Although an optical interface greatly reduces these effects, it doesn't eliminate them. This is where the Server's three unusual front-panel controls come into play. They change the waveshape in a specific way that counteracts the change in the waveshape introduced by the cable. Wadax calls this technique of reversing bit-waveform distortion Digital Feed-Forward Waveform Control. It essentially compensates for changes in the waveshape that oc-cur in the interface. To reiterate, the three front-panel adjustments are Speed (rise time), Output Gain (digital bitstream voltage), and Input Gain (voltage of the clock and control signals from the DAC to the Server). More specifically, the Output Gain control deter-mines the voltage at which the Server considers a binary “one” to be “one” or binary “zero” to be “zero.” As mentioned, you can store three settings of these controls as presets, called up from the front-panel touchscreen. Note that these adjustments don't change the data, only the shape of the data. (For more on how the shape of data affects the sound, see this issue's From The Editor.) The audio data transmitted through the Akasa interface are not formatted in the conventional SPDIF format. Rather, Wadax developed a proprietary data-transfer protocol in which the DAC controls the flow of data in blocks from the Server. The transfer speed is many times faster than that required by the audio data and remains constant regardless of the audio signal's native data rate, i.e., 44.1kHz/16-bit, 192kHz/24-bit, or any DSD frequency. When carrying higher data rates, the DAC simply commands the server to transmit blocks more frequently. The interface between the electrical signal and the optical in-terface was critical. To avoid degradation at this junction, Wadax developed a circuit built around a Neutrik connector and a 25-el-ement CNC-machined part that performs these optical-to-elec-trical and electrical-to-optical conversions. The part minimizes optical reflections as well as damps resonances. It is a massive, futuristic-looking device that is unlike any audio termination I've seen.
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Digital audio was supposed to work perfectly or not at all; re-moving analog-like variability was its raison d'être. Yet early on in digital audio it became apparent that identical bitstreams could sound different if the digital samples were put back together with even the most miniscule timing errors—jitter. Although 30 years later this mechanism is fully understood, it came as a shock to a mindset that viewed digital-audio data as just another form of digital information that could be transmitted or copied endlessly without error. However, unlike other forms of digitally repre-sented data, the end of a digital-audio system is an analog signal that is analyzed by our exquisitely sensitive hearing mechanism. Yet for all we've learned about digital audio, there's much that remains a mystery. One such mystery is precisely how adjusting the waveshape's steepness with the Wadax server's “Speed” con-trol changes the music's sense of pace and rhythm. The analog-like variability of digital signals has long fascinated me. When I was working in a CD mastering lab in the late 1980s, one of my jobs was investigating technical problems with mas-tertapes that could lead to issues with replicated discs. One day I learned that a customer, a small, independent music label, was unhappy with the sound of the replicated discs we had made. I spoke with someone in the band, who described how the repli-cated disc sounded different from the mastertape. This was the first time a customer had complained about the sound quality of a replicated disc. The sonic differences he described could not be the result of data errors on the disc. For starters, our QC department would have rejected any discs that had uncorrectable errors. CD error correction is extremely robust; it can completely and perfectly correct—not conceal through interpolation—up to 4000 consec-utive missing or corrupted bits. Second, such errors would show up as audible glitches, not as, for example, a reduction in sound-stage dimensionality. The first thing I did was compare the data on the customer's ¾" U-Matic CD mastertape with the data on the replicated disc, using a CD-ROM pre-mastering system. As expected, the data on the mastertape and the data on the replicated CD were identical.
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To the engineers I worked with, that was the end of the story. “Bits is bits,” they said, dismissing the musician's claims. Because the replicat-ed discs contained data iden-tical to the mastertape, they reasoned, our company had done its job, and any sonic differences were figments of someone's imagination. These guys were brilliant engineers. They had designed and built, from scratch, the two custom CD mastering machines in our factory—no mean feat. Yet, the audiophile in me was compelled to explore the question, so I cut a new glass master from the customer's CD mastertape on our sec-ond, newly designed master-ing machine and had discs replicated. This would enable me to listen to the two discs through the same CD player, something I couldn't do with the CD mastertape and the replicated disc (the master-tape could be decoded only by a Sony PCM-1630 pro-cessor). After verifying that the second disc contained the same data as the mastertape and the first disc, I listened to both discs on my home system. The two discs did, indeed, sound different—the second disc sounded smooth-er and more dimensional. Without telling the customer what I heard (or about the dif-ferent mastering machine), he reported that the second disc sounded like what he created in the studio. Now, I was really curious. I rented an analyzer that would measure the time periods of the pit and land structures on the CD. The analyzer graph-ically plotted the precise pe-riod of each of the nine dis-crete pit and land lengths that encode information. The first disc that sounded inferior had a much wider frequency dis-tribution of the signals gener-ated by the pits. The second, better-sounding disc, had a much narrower frequency distribution, indicating that the pit and land lengths were more precise. Moreover, look-ing at the raw signal from the CD player's photodetector revealed that the pit-to-land and land-to-pit transitions were cleaner and sharper on the second disc. In essence, jitter was embedded in the disc itself in the physical pit and land structures. It wasn't surprising that the second CD mastering machine produced less timing variation; its turn-table was controlled by a vast-ly more sophisticated and pre-cise rotational-servo system. Although this exercise was illuminating, it still didn't an-swer the question of how those timing variations on the disc made their way through an enormous amount of complex signal processing (the error-correction decod-ing alone is mind-boggling) to somehow affect the CD play-er's analog output signal. That question remains unanswered to this day. Al-though our knowledge of digital audio has advanced enormously in the last 35 years, there's still much to be discovered. The conundrum presented by the Wadax Ref-erence Server is simply the latest example. It shows us the limits of our understand-ing by raising more questions than it answers.
I am an audiophile. But even I think the science is actually clear. Psycho acoustics (belief of hearing differences in non double blind tests) AND economic incentives as reviewer to develop these myths.
But I post his in case there is stuff here that may make sense to the technically inclined. M.
