Music in the Round

As I took my valedictory lap around High End, the immense audio show held each May in Munich, Germany, it was clear that this year's event was an exuberant flowering of mature technology. I witnessed the dominance of hardware for LP playback, as well as analog amplifiers, many of them based on tubes, and passive loudspeakers with traditional cone-and-dome drive-units. And there was no shortage of excellent and impressive musical demonstrations. Still, I experienced no revelations, and heard no announcements of any new technology that might trigger a hopeful anticipation of the near future. It was as if HE2018 were reflecting on the past with reverence and commitment, rather than striving toward the future with innovation and adventure.

I know that I'm no longer a mainstream audiophile and that, compared to the bulk of the products shown at Munich—or, indeed, reviewed in the pages of Stereophile—I've gone off the rails. But the older I get, the more I prefer to listen to music without the constraints of old tech. The things that grab me are products that are the results of fresh ideas, critical reexaminations of accepted technology, and/or direct responses to market demands, whether obvious or as yet unrecognized. For the playback at home of multichannel music files, I saw nothing at High End 2018 that was as exciting as what follows.

miniDSP U-DIO8 multichannel USB to AES-EBU or S/PDIF interface There has been a serious impediment to the spread of multichannel playback among audiophiles. We have players for multichannel discs and servers/streamers for multichannel files, but at the outputs there is a fork in the road. One road—the HDMI inputs of audio/video receivers and preamplifier-processors—is an option generally avoided by audiophiles, though there may be no good reason for the rejection—there are indeed such products with high sound quality. The other road leads to a paucity of multichannel DACs. To repeat a rant from past columns, there are only three purpose-designed multichannel DACs: the inexpensive but capable miniDSP U-DAC8 ($299), the excellent exaSound e38 ($3850), and the impressive Merging Technologies NADAC+ ($12,000). But considering the prices, how much real choice is there for any individual potential buyer?

I understand the reluctance of the makers of audiophile gear to commit to developing a multichannel DAC. It's a problem of chicken and egg: In part, the market is small because there are not enough such products out there to create interest—which is why there aren't enough interesting products. A logical solution would be to make a workable setup from three independent stereo DACs—something Mytek HiFi took a stab at a while back (footnote 1). They offered proprietary solutions in which three of their stereo DACs (originally the Stereo 24/192, and more recently the Brooklyn) could be fed from a USB source via a USB hub to function as a six-channel DAC, as long as the master clock of one was daisy-chained through the others to keep all three in sync (footnote 2). Brilliant and successful, but wouldn't it be cool if you could press into service any of the many two-channel DACs now on the market? The problem is keeping the three DACs synchronized—and the vast majority of consumer DACs have no word-clock inputs and outputs.

Benchmark Media Systems has come up with a solution. They recommend a configuration in which a Lynx AES16e PCIe sound card ($699) provides 16 channels in and out at up to 192kHz. This card outputs two channels from each of its multiple AES/EBU outputs, and since each output carries data driven from the same onboard clock, all connected DACs are effectively synced to each other. Clearly, Benchmark thought it good enough to use in demos at hi-fi shows, and I'm told the results were impressive.

Benchmark warns that while this works with their own DACs, it's not a hard-lock sync. Due to differences among the client DACs, and thermal effects that accompany long-term playback, there is the potential for drift. In addition, a professional soundcard is not the practical solution I'm looking for because it must be installed in a PC; it can't be installed in a dedicated streamer or player.

Now there is such a solution: the miniDSP U-DIO8 ($299, including one multichannel output cable), which is available with either S/PDIF or AES/EBU output, both up to 24-bit/192kHz, and will connect with the USB output of any computer running Windows, Mac OS, or Linux (footnote 3). It's no surprise that it's the brainchild of Tony Rouget and miniDSP, who've been responsible for getting fiendishly simple and effective equalization products, some including Dirac Live, into the hands of adventurous audiophiles (footnote 4).

The miniDSP U-DIO8 is small: 6.3" wide by 1.2" high by 4.3" deep. It is also inexpensive: $299. Its front panel has a USB-B input and a blue LED power indicator. On the rear are a barrel connector for the 5V wall-wart power supply, and a DB25 connector that uses the Tascam-default pin layout for eight outputs and eight inputs of S/PDIF or AES-EBU, depending on the version purchased. Both versions of the U-DIO8 come with a suitable breakout cable: DB25 to eight XLRs, or DB25 to eight BNCs. (Buyers of the S/PDIF version must also buy three or four BNC-to-RCA adapters.) The only visible differences between the two versions—miniDSP sent me one of each—are a label on the rear panel and the connectors on the accompanying cable. No doubt miniDSP puts the input in front and the outputs out back for design convenience and for traditional signal-routing conventions but I think most of us would prefer to have all connectors on the rear panel.

The specs say it all. The USB streaming engine is an XMOS 16-core device that needs no driver for up-to-date Mac OSes and is compliant with Linux ALSA 2.0, but for Windows machines it requires the download and installation of an ASIO driver. This is all as expected, and the user manual provides clear guidance. The eight channels of digital output use four connections, S/PDIF or AES-EBU, and support word depths of up to 24 bits at sample rates of 44.1 to 192kHz. The U-DIO8's specified dynamic range is 128dB, and its THD+noise is –125dB. There are also eight channels of digital input via the same cable snake. These accept input sample rates from 32 to 216kHz, which might be useful for some calibration or measurement applications.

Testing
How to test something that has no controls, no options, and does nothing to the signal but convert it from USB data to an audio datastream? First, to determine if the U-DIO8 works as advertised is easy: Feed it a multichannel source, connect it to any three (or four) DACs and listen for audio from all channels. Check! Second, to find out if it is good enough that any user's choice of three attached DACs would perform to their full advantage, I used my three Mytek Brooklyn DACs with the U-DIO8 connected to my MacBook Pro computer. Double check! There was the clean, balanced, multichannel sound I expected.

However, to appreciate the capabilities and contributions of the U-DIO8, I had to try a number of different DACs to reassure myself that it wasn't constraining their sound in any way. Although the products I tend to cover in this column rarely end up on John Atkinson's test bench, I got him to measure the U-DIO8. Here's what he said:

"To put your mind at rest, I have attached two graphs. Fig.1 is a digital-domain FFT analysis of a loopback measurement from the Audio Precision's S/PDIF output to its S/PDIF input, with the test signal 24-bit J-Test data sampled at 44.1kHz. Fig.2 is with my MacBook Pro feeding the same 24-bit J-Test data to the miniDSP via USB and the latter's S/PDIF channel 1/2 output feeding the Audio Precision's S/PDIF input."

I saw no differences between the two graphs. John added that "the results were the same at 96kHz," and that the miniDSP "produces a bit-accurate output." That's good enough for me.

Listening
To appreciate the impact of the U-DIO8, beginning with the S/PDIF version, I decided to try several DACs spanning a wide range of prices. In addition to the trio of Mytek HiFi Brooklyn DACs (original version, $1995 each) already in-house, I borrowed from Schiit Audio three samples of their Modi 2 Uber ($149 each), from Cambridge Audio three samples of the DACMagic Plus ($349.99 each), and from Benchmark three samples of the DAC3 HGC ($2195 each).

The MacBook Pro was running JRiver Media Center (v24.0.30) and Roon (v1.5, build 323), each of which identified the output device as "USBStreamer," with audio-processing attributes up to the maximum resolution of the U-DIO8: 24/192. I used my Mac's Audio MIDI Setup to check that the channel mapping was correct, and clicked to play a 5.1-channel file. It was alive!

I compared the sound of each set of identical DAC triplets with that of my resident exaSound e38 and miniDSP U-DAC8, taking notes throughout. I wanted to determine whether, within the U-DIO8's range of resolution of up to 24/192, it would obscure any differences among the various trios of DACs, especially the sorts of differences that would make a shopper choose one DAC over the others. I didn't do this in the spirit of a DAC Shoot-Out, because that might demand a proper blinded test. Consistent with JA's measurements, my listening comparisons between a direct S/PDIF connection and sending signals via USB to the miniDSP and via S/PDIF to each DAC (in stereo) revealed no differences, and thus I had no preference as to which type of connection I used. The sonic signature of each model of DAC remained audible.

I began with the three samples of Cambridge DACMagic Plus, a well-received DAC that's relatively old but still in production. The sound, in the familiar context of my Manhattan system, surprised me: somewhat warm and spacious, with lovely detail and dynamics. The DACMagic Plus was much more relaxing to listen to over long periods than the miniDSP U-DAC8, which could develop a tiring brightness. The exaSound e38 didn't sound as warm as the DACMagic, but its highs seemed better resolved. At a total price of $1348.97 for three DACMagic Pluses and a U-DIO8, this combo struck me as the multichannel DAC the market has been waiting for, and one that I'd consider running through the multichannel analog input of my Marantz pre-pro. This will bypass the Marantz's digitization and processing while taking advantage of its volume control.

I got a similar impression from Schiit's three Modi 2 Ubers, but this time the pleasing warmth tended to soften details and dynamics more than did the exaSound e38 or the Cambridge DACMagic Pluses. It was a reasonable trade-off for the sharper detailing of the U-DAC8, and I could say that the differences between the Modi 2 Ubers and the miniDSP U-DAC8 were so distinct that personal taste in sound will be the most important factor in choosing between them. The total price of three Modi 2 Ubers and a U-DIO8 is $746, about halfway between the prices of my base reference U-DAC8 and the Cambridge-miniDSP package. I can easily imagine that many would find its sound and price just right for their taste and wallets.

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Footnote 1: There was a third route, based on using the multichannel analog output of a disc player, but that road has been increasingly less traveled due to the extinction of players with more than two analog output channels—or, for that matter, any analog outputs at all. Oppo Digital's recent decision to cease making disc players was the final straw.

Footnote 2: Playback Designs offers a similar but more elegant and expensive arrangement using their Designs USB-XIII Digital Interface with three Merlot DACs. See my September 2017 column.

Footnote 3: miniDSP, Hong Kong. Tel: (852) 2358-2066. Web: www.minidsp.com.

Footnote 4: While writing this column, I learned that miniDSP will release its own multichannel-capable SHD-series (Streaming High Definition) streamer-players with Dirac Live and Volumio built in.