Digital Processor Reviews

In the summer of 1999, Sony held a press event in New York City to mark the introduction of the Super Audio Compact Disc, then the sole domestic embodiment of the Direct Stream Digital (DSD) technology, jointly developed by Sony and Philips. The new format was hailed, in prepared remarks, by an impressive list of audio and music dignitaries: Nobuyuki Idei, then president of Sony Corporation; Steven Epstein, senior executive producer for Sony Classical; Yo-Yo Ma, appearing in a video created for the event; and Wynton Marsalis, appearing in person. All of the speeches—every single one of them—flattered SACD by likening its sound to that of the analog LP.

That was a long time ago. I'm sure that, by now, we can all forgive Sony for using the LP as a yardstick against which to measure an improved version of a format that, in 1983, they had said was already perfect. (Really. It's okay. Time to let go.) Besides, from the moment I heard the SACD at that press event, I was indeed impressed by its analog-like sense of musical flow and momentum. So impressed that I purchased, within months of the format's introduction, one of Sony's SACD players—which, at the time, were not exactly cheap (footnote 1).

A lot has happened since then. Just as significantly, a lot hasn't happened since then—namely the acceptance, by more than an insignificant sliver of the market, of SACD hardware and software. Yet DSD is getting another shot at consumer acceptance: Witness the recent promotion of DSD music files on the one hand, and of USB-input DSD processors on the other. My friends, DSD streaming has arrived—and so, too, has the DA-06 digital-to-analog converter ($4990), from Japan's 89-year-old Luxman Corporation.

Description
But there's more to this product than just one compelling if slow-to-mature format. While the Luxman DA-06 is one of about three dozen converters on the market that can process and stream 2.8224MHz and 5.6448MHz DSD files, it also supports, via its USB input, PCM with word lengths of up to 32 bits and sampling frequencies of up to 384kHz. (Its S/PDIF, AES/EBU, and optical inputs support up to 24 bits and 192kHz.) Additionally, PCM playback through the Luxman DA-06 can be optimized with a choice of three user-selectable digital filters, derived from different 32-bit interpolation functions. (Users can just as easily select between two different high-frequency-rolloff characteristics during DSD playback, but those filters exist only in the analog domain.)

At the heart of all this flexibility is the Burr-Brown PCM 1792A 32-bit converter chip, which also appears in Luxman's D-06 SACD/CD player. According to Luxman, digital inputs of 44.1, 88.2, and 176.4kHz are upsampled by this converter to 352.8kHz, while inputs of 48kHz and its mathematically related frequencies are upsampled to 384kHz. Digital signals arriving through the USB input are said to be streamed asynchronously.

Useful controls abound, and I was pleased to see that Luxman has put them all on the DA-06's nicely styled front panel—and dispensed altogether with a remote-control handset, which I persist in regarding as the devil's plaything. A knurled, six-position rotary switch at the far right of the front panel selects among the various digital inputs—two optical, two coaxial, one AES/EBU, one USB—and a pushbutton toggle to its left can be used to disable the DA-06's digital output, in an effort to enhance analog-output quality. Still farther to the left is a notably clear, seven-segment LED display for sampling rates and word lengths (the latter functioning only with S/PDIF inputs); an adjacent pushbutton offers four levels of display brightness—or, for you empty-glass types, darkness.

At the far left of the front panel, a simple, two-position pushbutton is the sole means of turning the DA-06 on and off—another blessing to the user who sees little point in paying for the complexity of on/off/standby switching, and who prefers knowing, without ambiguity, when "Off" means off. Beyond that, the Luxman's four remaining pushbuttons were those I found most useful: controls for inverting absolute signal phase, selecting the digital PCM filter, and selecting the analog DSD filter, plus an Enter switch, which enables the user's choice in all three functions.

The DA-06's rear panel is straightforward. Single-ended analog output signals appear on a pair of RCA jacks, balanced signals on a pair of XLR sockets (pin 2 is hot). Two RCA jacks, two TosLink jacks, a USB Type B socket, and an XLR socket accept digital inputs of various types, and digital output is available from an RCA or a TosLink jack.

The DA-06's case consists of a hefty, well-finished steel bottom plate to which various thinner steel plates—for both structure and shielding—and the alloy front panel are bolted. A thin steel sleeve, finished in textured paint, covers the works: nicely executed, if a slight notch below what I would expect in a $5000 product. Interior build quality is superb, with most of the circuitry divided among three main boards, for analog output (the largest board), digital processing, and the power supply. Parts quality is good insofar as I can tell, with Luxman's own bespoke capacitors in many positions, and an especially beautiful, copper-wrapped mains transformer at the power supply's electrical heart.

Installation and setup
Being not too big, too heavy, or possessed of controls too inscrutable, the Luxman DA-06 was cake to install. My Apple iMac recognized it the moment they called to one another across a 2m-long WireWorld Revision USB cable—the processor appeared in the computer's System Preferences/Sound window as "Luxman DA-06"—and has never failed to do so in the days since, with no need for rebooting computer or processor.

As for playback software: I normally rely on Stephen Booth's very cost-effective Decibel (v.1.2.11) for all music files, and on Apple iTunes for streaming FM broadcasts, but at the time of writing neither program supported DSD. I deferred to the DSD enthusiasts among my colleagues and friends, who all pointed me toward Audirvana Plus ($74), v.1.5.12 of which has now imprinted itself on the magnetic dust of my hard drive (which is not quite the same as saying "I own it," but please humor me and play along). I suffered, early in the review, some concern that either Audirvana Plus or the Luxman DAC did not support MP3 files, as I was unable to stream music from my favorite Internet radio station; as it turned out, my first attempt at doing so came during one of WCKR's experimental-music hours—I had chanced on a period of extended silence written into a score. Subsequent broadcasts sounded fine.

Except where indicated otherwise, all of the following observations apply to the Luxman DA-06 with its two adjustable filters in their normal settings: P-1 for PCM [see the "Measurements" sidebar—Ed.], D-1 for DSD.

Listening
Reality prevails. And while I'm sure there exist hardcore enthusiasts who acquire every DSD file that's commercially available, and who make those files the predominant if not exclusive medium for all of their listening sessions, the digital-music "collections" of most audio enthusiasts are overwhelmingly dominated by PCM recordings: In the field, those are what most Luxman DA-06 converters will spend most of their time converting.

Consequently, although I laid in a good selection of DSD files chosen specifically for this review, I spent most of my reviewing time using the Luxman DA-06 for everyday listening: mostly 16-bit/44.1kHz PCM files, with a smattering of 24/96 and 24/192 PCM files. Used in that manner, the Luxman suggested an idealized and vastly more flexible version of the affordable and consistently listenable Halide DAC HD, which has become my USB reference during the past year. The Luxman went well beyond the Halide by sounding generously explicit, providing musical and sonic details in abundance and presenting them in a soundfield notable for its openness and general lack of murk. Still, the DA-06 had good substance, with a tonal character that was slightly—almost imperceptibly—warm and round, even with that default filter.

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Footnote 1: The SCD-777ES was initially priced at $3500, dropping to $2500 by the time of our review—Ed.