Direct Stream Digital (DSD) is the trade name Sony and Philips chose for the encoding scheme of pulse-density modulation (PDM) used for their Super Audio CD (SACD) optical-disc format, introduced in 1999. In contrast to pulse-code modulation (PCM), the original low-sample-rate, multibit format used for the Compact Disc (introduced in 1982), PDM is a high-sample-rate, single-bit format. However, SACD failed to win mainstream acceptance outside the audiophile community. Part of the problem was that few non-classical record labels ever adopted SACD, so few recordings were available to take advantage of it. Furthermore, while many SACDs were hybrid SACD/CDs containing both PCM and DSD layers, if you wanted to hear the DSD layer, you needed an SACD player. The combination of a small number of titles and the need for special hardware to play them helped ensure that SACD remained a niche format.
Now, if the sheer number of high-end DACs that include DSD playback is any indication, DSD seems to be making a comeback. One of the most interesting DSD-capable DACs on the market came out in 2014, after seven years of development by computer engineer and audiophile Ted Smith. While Smith was responsible for designing the processor, PS Audio CEO Paul McGowan and Arnie Nudell, founder of Infinity Loudspeakers, completed the final voicing. What distinguished the resulting DAC, the PS Audio PerfectWave DirectStream, from much of its competition was the fact that it used 1-bit processing for its digital-to-analog conversion -- which meant it could natively accept DSD as well as PCM signals, and convert them all to ten times the base sampling rate of DSD (explained more below). The DirectStream earned considerable attention from the audio press, but its price of $5999 USD kept it out of the reach of many. To make their technology more accessible, PS Audio released a scaled-down version, the DirectStream Junior, that retains much of its senior’s technology, and cut the price to $3999. A couple of months ago, a DirectStream Junior arrived at my house for review.
One way PS Audio was able to keep the DirectStream Junior’s (DSJ) price low was to make some changes in the case. The DirectStream’s case comprises various cast pieces, machined parts, a hand-painted cover, and a touchscreen display. In contrast, the DSJ is housed in aluminum extrusions that are easier to assemble, with a Plexiglas cover and a simple OLED display. But while PS Audio may have found a way to lower building costs, they haven’t sacrificed much in the way of appearance. Weighing 18 pounds and measuring 17”W x 14”D x 2.75”H, the DSJ not only feels sturdy, it also looks clean and modern. It’s a beautifully crafted component that should look at home in just about any room.
Inside the DSJ is a single printed circuit board, instead of its forebear’s separate boards for the digital and analog circuits and the Bridge II network card/power supplies. Furthermore, whereas the DirectStream has multiple power transformers, the DSJ has just one. Finally, the DirectStream’s output stage includes high-speed, high-current analog video amplifiers driving an output transformer; the DSJ uses similar passively filtered amplifiers that drive the output directly, with no transformer.
The DirectStream’s core technology, specifically the DSP processor designed by Ted Smith, is the same as in the DSJ. In fact, this technology is unique to PS Audio -- no off-the-shelf chipset can do what Smith’s DAC can. As a result, he instead used a field-programmable gate array (FPGA) chip -- essentially, a blank chip that can be programmed to do what its designer wants.
So what exactly does Smith’s FPGA do? According to PS Audio, it takes all incoming PCM and DSD data and synchronously upsamples it to 30 bits at 28.224MHz. This is ten times higher than the standard DSD rate of 2.8224MHz, and 640 times faster than PCM’s 44.1kHz. This extraordinarily fast sampling rate was chosen because it’s the lowest common rate attainable through integer upsampling of 176.4 and 192kHz PCM files. Next, the signal is downsampled to 5.644MHz, or DSD128, which is twice the base DSD rate of DSD64 (i.e., 64 times 44.1kHz), and converted to single-bit PDM before being sent to a low-pass filter at the output stage. The purpose of downsampling to DSD128 is that it allows the low-pass filter to start rolling off at 80kHz -- according to PSA, anything higher would introduce jitter. Apparently, one of the inherent advantages of single-bit processing is that producing an analog signal from such a high sample rate can be achieved quite easily by using a simple low-pass filter, as opposed to the brick-wall filters used for PCM, which can negatively affect the sound when poorly implemented.
PS Audio also approaches jitter somewhat differently from how many of its competitors do. Rather than using multiple master clocks to reclock all incoming data, the DSJ uses a single master clock. According to PSA, multiple master clocks can be difficult to synchronize; to avoid this, they instead use a low-phase-noise, low-jitter clock designed by Crystek to eliminate the need for synchronization altogether. The company claims that this means that digital sources of just about any quality and jitter level sound virtually identical. In other words, the sound quality is far less dependent on the quality of the source or the cables used to make the connections.
In addition to its AES/EBU (XLR), S/PDIF (coaxial), TosLink (optical), and I2S (via HDMI) digital inputs, the DSJ can also connect to a computer via USB, or to a home network using the Bridge II, PS Audio’s newest network card. With the Bridge II and USB connections, the DSJ can be controlled with an iPad, iPhone, or Android device. Since fewer and fewer listeners play CDs, the inclusion of these features is a must for any high-end DAC.
The HDMI input can be used only to transfer I2S data from compatible sources such as PS Audio’s own PerfectWave Memory Player CD/DVD transport, forthcoming DirectStream Transport, or NuWave phono preamplifier. It will not work with other HDMI sources, as it doesn’t comply with any HDMI standard. However, PSA makes its I2S standard public and, according to the company, other manufacturers have adopted it; buyers will need to investigate to determine whether their source components can use this connection.
In the DSJ’s manual, PS Audio recommends using its USB input, which will support PCM up to 24-bit/352.8kHz, as well as DSD64 and 128 via DSD over PCM (aka DoP). Other digital inputs include the Network Bridge II, which requires a network and associated hardware, such as a router; and XLR (AES/EBU), RCA and TosLink (both S/PDIF), and HDMI (I2S). The TosLink input accepts PCM up to 24/96, but not DSD. The XLR, RCA, and TosLink inputs support DSD64 (via DoP) and PCM up to 24/192. The HDMI (I2S) input supports 24/192 PCM and up to DSD128; however, the nifty thing about this is that it can support DSD via DoP, in addition to native DSD streaming, though you’ll need a source component (such as PS Audio’s forthcoming DirectStream Transport) or the appropriate software on your computer to supply the datastream.
Finally, the DSJ has both single-ended and balanced outputs that can feed directly into your preamp or power amp. This means that, because the DSJ also has a built-in volume control, you can use it as a preamp on its own, negating the need for a separate preamp. The DSJ also has what PS Audio calls a “zero-loss volume control,” which, it claims, will maintain full-resolution, bit-perfect sound at almost any output level.
The DirectStream Junior was connected to a Bryston B135 SST2 DAC-integrated amplifier using Kimber Kable Tonik interconnects. AudioQuest Comet speaker cables terminated in banana plugs were used to link the B135 with Revel Performa3 F206 floorstanding loudspeakers. I used an NAD C 542 CD player as a transport feeding digital data to the DSJ through an i2Digital X-60 coaxial cable. Serving as a secondary digital source was an Apple MacBook computer connected to the DSJ with an AudioQuest Forest USB cable. All electronics were plugged into an ExactPower EP15A power conditioner/regenerator.
As I often do when evaluating a new component, I played the War Dance from Respighi’s Belkis, Queen of Sheba -- Suite, performed by Eiji Oue and the Minnesota Orchestra (HDCD, Reference RR-95CD). The rhythm of the drum was full and powerful, sounding natural as it decayed under the flute’s almost whimsical dance. One thing that quickly became apparent was that the DSJ didn’t imprint music with its own character, but stepped aside to open a clear view into the music. With War Dance, this made it easy to imagine hearing this performance in person.
What places the DSJ among the best DACs I’ve heard is that it lacked the harshness or edge of most digital source components. The triangle and winds in The Pines of the Villa Borghese, from Respighi’s The Pines of Rome on the same disc, shimmered and shone with pristine upper registers that were the antithesis of sharp or grating. I’ve never heard digital playback that could be mistaken for analog, but in terms of the ease and fluidity of its sound, the DSJ captured some of analog’s greatest virtues -- a smoothness and ease to the sound -- while preserving the low noise floor and clarity of the finest digital playback.
One noun that kept coming up in my listening notes for the DSJ was space -- something this DAC consistently produced across a range of recordings. With “Ave Generosa,” from A Feather on the Breath of God (CD, Hyperion CDA66039), contralto Margaret Philpot’s voice soars to the ceiling of London’s Church of St. Jude-on-the-Hill, where this recording was made over three decades ago. This chant was composed by the 13th-century German abbess and mystic Hildegard von Bingen, and the DSJ was sublime in its ability to preserve the acoustic of St. Jude and the grandeur of the music in this beautiful recording, and helped deliver the composer’s intent: to connect the listener with something higher. Again, the DSJ was notable for what it didn’t do, moving aside to let the music pass through unadulterated. Could the DSJ make me forget that I was listening to music in the comfort of my home rather than in an English church? Of course not -- but it was still commendable for making it easier for me to imagine myself being there through its ability to convey detail and space in a natural, believable way.
I then tested the DSJ’s ability to reproduce a sense of space with well-recorded music, of which my music collection contains perhaps no better example than “So What,” from Miles Davis’s Kind of Blue (CD, Columbia/Legacy CK 64935). It amazes me that an album recorded in 1959 can still, almost six decades later, serve as a benchmark for pinpoint imaging and soundstage coherence. Through the PS Audio, this track was as engaging and lucid as I’ve ever heard it from CD, with instrumental outlines so clean and sharp that the work of Davis & Co. in Columbia’s 30th Street Studio, in Manhattan, was, sonically speaking, nearly beyond reproach.
With “Inertia Creeps,” from Massive Attack’s superb Mezzanine (CD, Virgin 8 45599 2), I’m not sure the PS Audio could have been bettered in its ability to deliver the track’s tight, fast-paced, percussive rhythm, with its pristine clarity and wide, upfront stage. Once again, the DSJ sounded incredibly fluid, and helped give the music an amazing feeling of pace and vitality.
I also spent some time listening to DSD files through the DirectStream Junior, courtesy the 2L record label, based in Norway. (Although these were DSD files, the original recordings were made using PCM.) Listening to Vivaldi’s “Che giova il sospirar,” RV679, sung by soprano Tone Wik accompanied by recorder player Alexandra Opsahl, bassoonist Per Hannisdal, and the ensemble Barokkanerne (included in the collection Bellazza Crudel, DSD128, 2L), was a treat through the DSJ. The performers of this chamber cantata occupied a deep, wide stage at the front of my room that extended past the outer edges of the speakers and beyond the front wall. The violin was airy, the sense of space around it palpable -- this recording showcased the DSJ’s extraordinary transparency.
The strings in the Finale -- Presto of Haydn’s String Quartet in D, Op.76 No.5, performed by the Engegard Quartet (16-bit/44.1kHz FLAC or DSD128, 2L), were infectious, reproduced by the DSJ with amazing clarity and sounding sharp and incisive as the music moved at a frantic pace. Compared to the PCM version of this recording, the DSD128 seemed to have a touch more energy, which gave it an extra bit of presence. The difference was subtle, but as I switched back and forth between them, I consistently found I preferred the DSD128 file.
Just before the DirectStream Junior’s arrival, I had completed a review of Bryston’s BDA-3 DAC ($3495), which the DSJ replaced in my system. I was able to compare these two similarly priced but differently designed models side by side. These DACs are fairly different in design, notably because the PS Audio converts all incoming data to DSD (PDM), whereas the BDA-3 processes DSD (and PCM) natively, but doesn’t convert PCM sources to DSD before outputting them as an analog waveform.
I spent considerable time listening to these two DACs and found that while they sounded similar, some aspects of their sounds will leave shoppers preferring one to the other. With “Backstage with the Modern Dancers,” from the Great Lake Swimmers’ Ongiara (CD, Nettwerk 6700-30691-2), the double bass had a touch more weight and impact through the Bryston BDA-3. Both DACs effortlessly revealed the clarity, image focus, and detail in the opening of this track, but as I listened to the PSA DSJ, my attention was drawn more toward the highest notes resonating from the strings of the acoustic guitar. They sounded airier, and thus better emphasized the feeling of isolation that permeates this tune. It wasn’t that the BDA-3 didn’t sound open -- but as I kept switching between the DACs, I found I preferred the sense of space conveyed by the DSJ.
In “Louis Collins,” from David Grisman and Jerry Garcia’s Shady Grove (CD, Acoustic Disc ACD-21), the bluegrass ensemble seemed a touch closer to me through the Bryston than through the DSJ, which put them slightly farther back on the stage. Through the BDA-3, Garcia’s acoustic guitar was a bit fuller in its lowest registers, and, as with the double bass in the Great Lake Swimmers track, this gave the instrument a bit more body and warmth. For the most part, I thought the DACs sounded similar, particularly in their excellently transparent and revealing natures -- a neutrality that passed along the music without editorializing.
“m.A.A.d. city,” from Kendrick Lamar’s good kid, m.A.A.d. city (CD, Aftermath/Interscope B001753602), features booming bass, and while I was curious to hear how the two DACs reproduced it, I couldn’t hear much of a difference. The Bryston did sound marginally closer on the stage, but the thumping bass was solid and impactful through both DACs, neither sounding fat or overblown. Through both, this track and the entire album sounded clean and open, making it easy to hear deeply into the recordings.
Once again I cued up Respighi’s War Dance, and found the DACs equally adept at preserving the explosive dynamics and spacious soundstage so well captured on this recording. At any given moment, I was pretty satisfied with whichever DAC I was listening to; no obvious winner emerged, and both are among the best I’ve used in my system -- if there’s a DAC on the market that sounds significantly better, I’d love to hear it.
With their DirectStream Junior DAC, PS Audio has managed to offer the technology developed for the DirectStream “Senior” for only two-thirds the price. The DSJ is a product that approaches digital processing in a way different from many of its competitors -- pretty remarkable, given the maturity of digital playback. If there was ever an example of thinking outside the box, the DSJ is it.
However, what makes the DSJ special isn’t merely technological, but that that technology is used in the service of outstanding sound quality to make it among the best-sounding DACs I’ve heard. The DSJ is an incredibly detailed- and wonderfully transparent-sounding component whose fluid, natural sound is musical and highly addictive. During my time with it, I enjoyed revisiting many discs and files, simply to hear how they’d sound through the DSJ. It never failed to impress. If you’re in the market for a new DAC and want topflight sound, it would be a mistake not to hear it.
. . . Philip Beaudette
PS Audio PerfectWave DirectStream Junior DAC
Price: $3999 USD.
Warranty: Five years parts and labor.
4826 Sterling Drive
Boulder, CO 80301
Phone: (720) 406-8946