In the context of discussing computer audio, it takes only the mention of three letters—“U,” “S,” and “B”—to raise John Mingo’s blood pressure. Since the Montana-based Mingo started Baetis Audio in 2011, he’s been expounding, explaining, clarifying, and ranting about the importance of the type of interface employed for getting digital data from a computer to a DAC. He bristles at the perception that USB is the “standard” simply because those ports are mostly what are found on the computers audiophiles usually use to play their music files. I reviewed the Baetis Revolution II ($2995) nearly two years ago, in Issue 240, and found that high-resolution material played via SPDIF—the output derived directly from that machine’s motherboard—provided the best digital sound I’d ever heard. In Baetis’ current line of servers, the Revolution III ($4495), the XR3 ($7995), and the Reference ($13,995), this playback approach has been refined and advanced, especially in the flagship model. Multiple aspects of the newer components’ engineering are responsible, but a mother-daughter story is central.
When it comes to connecting a server/computer’s motherboard and a DAC—whether that DAC is internal (in the same box as the motherboard) or external to it—there are a limited number of possibilities. First is the ubiquitous Universal Serial Bus, introduced long ago to attach peripherals, such as a printer, to a computer. “The problem with USB,” says John Mingo, “is that the process of containing an audio signal—inherently PCM—within a USB signal creates digital noise. Additionally, the DAC can’t convert USB to analog; there must first be a USB-to-PCM conversion before the signal gets to the digital-analog section of the DAC. Additional circuitry contains the potential for more noise. PCI cards have been used to reduce the noise of the USB output but this does not eliminate the need to have a ‘converter’ section in the DAC or in a separate converter box.”
A second alternative is HDMI, which is generally the best option for multichannel, though there are concerns about audio parameters (e.g. jitter) with an interface that’s been optimized for video-data transmission. Third are the various SPDIF options. TosLink is an optical system that’s inexpensive to manufacture but doesn’t perform nearly well enough in high-end applications. The two electrical SPDIF types are of much greater interest to Baetis and to other computer audio designers. The standard coaxial SPDIF—for the remainder of this review, simply referred to as SPDIF—can be terminated in either an RCA or BNC connector. The latter is superior electronically, mechanically, and sonically; this interface was the one that gave such outstanding results with the aforementioned Revolution II. The third SPDIF variant is AES/EBU—AES, for short—a balanced construction with three-pin XLR connectors. Michael Ritter at Berkeley Audio Design and others urged Baetis to experiment with implementing AES, which operates at a significantly higher voltage than SPDIF. AES sounded great to Mingo and his listening panel—better than standard SPDIF. And here’s where the mother-daughter story begins.
John Mingo contracted with a small Canadian company to produce a proprietary circuit board to allow implementation of the AES option. Again, Baetis begins with a SPDIF signal straight from the motherboard, with no creation of a USB signal. “If you’re going to convert SPDIF into AES, everybody knows you’re going to need a transformer, a device to change 75-ohm SPDIF into 110-ohm AES,” he explained. The Canadian firm created the necessary daughterboard, the details of which are proprietary Baetis trade secrets. As initially configured, the SPDIF signal didn’t pass through the daughterboard—if a user wanted to switch from AES to SPDIF, it was necessary to open the Reference’s case. To facilitate SPDIF-to-AES comparisons, a second iteration of the daughterboard, with a different transformer, was developed that took the output directly from a motherboard header and allowed either a BNC connector to send out a SPDIF signal or an XLR connector to send out an AES signal, though not both at once. The quality of the AES signal improved, presumably as a consequence of the new transformer. “But the construction of this new circuit board allows the SPDIF signal to be improved by the transformer in terms of the shape of the digital waveform on the oscilloscope, as well. Meanwhile, the amplitude (voltage) of both SPDIF and AES are increased, and rise time is reduced.” So, although the Reference is the only Baetis product with an AES/EBU output, all three models employ a variation of the same custom daughterboard, for the benefits heard with SPDIF. Mingo elaborated: “This leads you to think about what the transformer on the daughterboard is doing. It is, of course, transforming SPDIF to AES, but it is also transforming the quality of both signals.”
There are additional aspects of the Reference’s engineering worth noting beyond those related to the digital interface. The CPU at the heart of the computer is more advanced than with earlier models (a four-core Intel i7) and the motherboard is a newer iteration, as well. The cooling system is new, a “hybrid” design with both a single fan and a series of heat pipes that lead from the CPU to the enclosure’s fins. A “premium Japanese-made Blu-ray optical drive” accepts discs for ripping. There’s a good deal of EMI treatment throughout the unit, both of the “absorbing” and the “shielding” varieties, with especially heroic attention devoted to one pair of USB 3.0 ports—the path to which is from a single header on the motherboard and is completely EMI shielded. Stillpoints Control Footers provide mechanical isolation.
On the outside, the Baetis Reference is an appealingly proportioned full-sized component (unlike the smaller Revolution models) measuring 17 1/8" x 12 1/2" and standing 5 1/4" tall on the Stillpoints. Finish options are black and silver. On the front panel is a power button with associated indicator light, the slot to load discs, and a small black window that could receive instructions from an IR remote (which typically isn’t included or recommended). The rear panel sports the receptacle for a Neutrik DC connector and, next to that, a raised area with the AES output, SPDIF output (with BNC termination), and a USB output. To the far left are additional connections including two HDMI outputs, four USB 3.0 ports, two USB 2.0 ports (appropriate for keyboard and mouse), two Ethernet ports, a DVI port, and two antenna connections for WiFi. On the right side of the Reference, between two fins, is one more pair of USB 3.0 ports, the ones with the more elaborate shielding mentioned above—Baetis notes that one of these would be a logical choice to transmit a DoP (DSD over PCM) signal. The solid-state drive holding the computer’s Windows 8 operating system is internal of necessity, but Baetis believes that all storage drives should be external to protect against EMI (and to make replacement easier). Even the internal SSD is easy to replace, as it’s held in place by Velcro. When (“not if,” Mingo notes, realistically) the SSD malfunctions, Baetis can just pop a new one in the mail; there’s no need to take the entire server into a repair shop, or ship it back to Montana.
Baetis provides all the accouterments you’ll need to get up and running. This includes the mandated Uninterruptable Power Supply (Baetis warns you that the warranty is void if the UPS isn’t used). Also provided is a 3TB external hard drive for media storage—a decent amount of room to start with, especially if you’re not archiving movies. There’s even a wireless mouse and keyboard to use when tagging, or anytime if you don’t get around to setting up a tablet as a remote control. The Reference, as do all Baetis computers, comes loaded with the latest stable version of JRiver Media Center, widely regarded as the most robust music organizing and playback software on the market. The company also provides a level of customer support that is utterly unique in my experience as an audiophile. The “quick start” guide that comes in the box implores the new owner to schedule (typically within a day) a live, one-on-one instruction session. When the computer is turned on, a Baetis technician clicks an icon allowing remote operation of the computer while you receive simultaneous guidance on the phone. A significant upgrade, some previous Baetis owners may conclude, is that the instruction is no longer provided by John Mingo who could get, shall we say, a bit…testy. Instead, new owners are taught by Montréal-based Joe Makkerh, who has been a JRiver beta-tester for a decade, and is an exceptionally patient and talented teacher. Reference owners on average require just over seven hours of instruction to get comfortable using the machine. To allow users to continue developing their JRiver skills (there are seemingly endless levels of functionality), the cost of the Reference includes unlimited support for three years after purchase.
In keeping with my earlier comments, Baetis—OK, John Mingo—has strong opinions about which DACs are most suitable for use with the Reference. Not surprisingly, he feels that “USB-centric” DACs are not likely to be ideal; many of the DACs and pre/pros that he recommends don’t even have a USB input. Both Berkeley DACs, three products from Bel Canto (including the modestly priced DAC 1.7), and the Anthem D2v (my usual processor) are Mingo-approved. His recommendations also include units from dCS, EMM, Audio Research, Soulution, Briscasti, among others. (The list is growing, so give Baetis a call if you’re considering a Reference and want to know if your AES-equipped DAC is considered a good match. Certainly, there’s no point in paying big bucks for a Reference if you won’t be using the AES output for the playback of stereo digital files.)
I’ve employed the Baetis Reference server as my primary music source for more than three months, and have been using it for speaker evaluations—the Crystal Cable Minissimos and the PSB Imagine T3s—for music reviews, and for plenty of listening for pleasure. (I’ll note that the Baetis does a spectacular job with video, but that’s not my focus here.) I made brief comparisons between the Reference and the Baetis Revolution II, which I’ve had in my system since late 2013. The relevant matchups involved SPDIF on the Revolution II vs. the same interface on the Reference, and HDMI, both stereo and multichannel, on both machines. The differences were not large but more apparent with SPDIF, where the Reference bested the Rev II by perhaps ten percent. Both units sounded very good, but the former manifested more transparency and slightly greater complexity of musical textures. Distinguishing between the performances of the two components’ HDMI outputs was close to impossible. Bottom line: If you already own a Baetis Revolution II and don’t plan to use an AES output to send digital data to your DAC, there’s no good reason to make the sizable investment to upgrade to a Reference.
Mostly, I tried to assess the differences among the Reference’s range of output interfaces—USB, HDMI, coaxial SPDIF, and AES/EBU. For some of these comparisons, I also had on hand the original SACDs from which the files had been ripped. All digital-to-analog conversion was performed by my Anthem D2v processor’s AKM DAC chipset. Digital cables included Transparent Premium HDMI cables, a Shunyata Anaconda SPDIF wire, and a Shunyata Anaconda AES/EBU cable.