December 15, 2009
Ayre Acoustics QB-9 USB Digital-to-Analog Converter
2009 is proving to be a watershed
year for computer-based audio. High-performance audio companies have begun in earnest to
unleash their creativity, endeavoring to maximize the performance opportunities computer
audio can provide. Likewise, software such as Sonic Studios Amarra is becoming
available to ensure "bit-perfect" integrity and native-rate decoding. Riding
this wave of momentum, the first-ever Computer Audiophile Symposium was held in Berkeley,
California, in June; in October, the Rocky Mountain Audio Fest featured multiple computer
audio seminars; and Ayre Acoustics has introduced the subject of this review, the QB-9 USB
D/A converter ($2500 USD).
Ayre Acoustics, of Boulder, Colorado, has lately been on a
roll. Quietly inventing elegant solutions to problems inherent in high-performance sound
reproduction, Ayre unhurriedly releases one or two new products a year to appreciative
connoisseurs around the world. Formed in 1993 by Charles Hansen, formerly a designer of
loudspeakers at Avalon Acoustics, Ayre builds its solid-state audio equipment on three
principles that were encoded in its corporate DNA on Day One: all circuits must be fully
balanced, zero-feedback designs; power supplies play a paramount role; and, with customers
and dealers -- even reviewers -- always follow the Golden Rule.
Ayre spent most of 2007 and 2008 introducing its
state-of-the-art, megabuck R series -- the MX-R monoblock and KX-R line stage, which won
awards and rave reviews. For 2009, Ayre has attacked the less expensive end of its lineup,
upgrading a trio of older products to MP versions. Its disc spinners (the C-5xeMP
and C-7xeMP) now feature Minimum Phase digital filters, while its K-5xeMP
preamplifier uses a new Maximum Performance analog output stage. All earlier editions of
these three products are fully upgradeable -- a long-term practice maintained by Ayre.
Interestingly, the advancements incorporated in those upgrades originated with Ayres
newest product and the first member of the companys new 9 series, the QB-9.
The QB-9 is a member of a component category cryptically
referred to as a USB DAC -- i.e., a universal serial bus, digital-to-analog
converter -- the sole purpose of which is to turn a computer into a source component
equivalent to a digital transport by tethering a PC or Apple Mac to an audio system via a
USB cable. Surprisingly, the QB-9 is Ayres first-ever DAC. Notwithstanding
Ayres position for the past decade as a leader in digital audio technology, all its
prior digital source components -- CD players, DVD players, universal two-channel audio
players -- have been self-contained, single-chassis devices. According to Hansen,
Ayres focus on the one-box solution allowed it to bypass the unavoidable
jitter-inducing flaws inherent in the Sony/Philips Digital Interface Format (S/PDIF). But
how can something as lowbrow and pedestrian as the ubiquitous USB connection change
Ayres approach?
Big things in small packages
Arriving in a box of brown cardboard (recycled and
recyclable, rather than bleached white), the QB-9 is sheathed in a thick polyethylene bag
and suspended in air between two opposed "trampoline-style" frames. Not only
does this Ayre Suspension System successfully reduce any chance of shipping damage, it
minimizes the use of packing materials and shipping weight, all while helping to conserve
the environment.
Cute rather than sexy, the QB-9s appearance is sleek
in its silver or black livery. Of a compact size at 8.5"W x 3"H x 11.5"D
and tipping the scales at 5 pounds, the QB-9 could well be described as a
"quarter"-sized component. By comparison, the full-size Ayre C-5xeMP,
my long-term reference disc spinner, is just over twice as wide, almost twice as tall, and
weighs five times as much. In any event, the QB-9s size makes it suitable for
placement almost anywhere -- in a rack, on a desktop, paired with a headphone amp, you
name it.
Being a dedicated USB D/A converter, the QB-9 has a minimum
of connections, the primary being the single USB input (the squarish Type B connector
designed for computer peripheral devices), which currently accepts signals of up to 24
bits at sample rates of 44.1kHz (i.e., the "Red Book" Compact Disc
standard), 48kHz, 88.2kHz, and 96kHz. To complete its D-to-A mission, the QB-9 also has
two pairs of analog audio outputs, balanced (via XLR connectors) and single-ended (via
RCAs). Theres an IEC connector for the power cord, and two AyreLink Ports to enable
various Ayre products to be daisy-chained using standard two-line telephone cords to
control an entire audio system.
Tech-laden
Charles Hansen emphasizes that his sole goal in designing
the QB-9 was to achieve the best possible audio playback from computers for the least
amount of money. Despite such a narrowly focused design brief and the products small
size, the QB-9 is packed to the gills with original thinking and unique technology. In
addition to zero feedback and fully balanced circuits, the QB-9 is the first product from
anyone to combine Streamlength Asynchronous USB data delivery, Minimum Phase digital
filters with single-pass 16x oversampling, galvanically isolated grounding between the USB
receiver and audio boards, and an EquiLock analog output circuit. It all sounds
impressive, but what does such technology really represent?
For the QB-9, everything begins with the Streamlength
Asynchronous Transfer Mode for USB input, the brainchild of Wavelength Audios Gordon
Rankin. By taking advantage of the asynchronous-delivery alternative embedded in the USB
protocol (Rankin invested over 900 man-hours in writing proprietary code to allow the
Texas Instruments TAS1020B Stereo USB Audio Interface chip to operate asynchronously),
Streamlength facilitates a high-precision, fixed-frequency clock in an outboard DAC to be
the master to which the computers output is slaved, resulting in vanishingly low
jitter. A white paper expounding the technical aspects and performance benefits of
Streamlength is available on Ayres website.
Recognizing the inherent superiority of this delivery
system -- at least for those who believe it better to avoid a problem in the first place
than to try to fix it afterward -- Ayre is the first licensee of the Streamlength
asynchronous delivery system. Hansen stresses that it was Streamlengths potential
for ultra-low jitter that enabled the QB-9 to sidestep the limitations in the S/PDIF
standard and match the jitter performance -- measured in single digits of picoseconds --
achieved by Ayres one-box disc players. The QB-9 currently accepts 24-bit/96kHz
digital files, but will support higher-resolution files of up to 24/192 in the near
future.
Having decided to build a standalone DAC for computer
audio, and intrigued by Peter Cravens 2004 paper on "apodizing,"
"minimum-phase" digital filters published in the Journal of the Audio
Engineering Society, the Ayre engineering team decided the time was ripe to
investigate new approaches to digital filters. Minimum-phase filters primarily differ from
their linear-phase brethren (the standard design used in over 99% of all digital recording
and playback devices) in that they avoid pre-ringing. Craven hypothesizes that it is this
unnatural pre-ringing that has crippled digital media, especially the "Red Book"
Compact Disc, a standard compromised from the start. Using a C5-xe disc player as a test
mule, and taking advantage of the flexibility offered by Xilinxs Field Programmable
Gate Array (FPGA) chips, the Ayre team spent months experimenting, comparing apodizing
filters, myriad other minimum-phase designs, and the filterless approach many prefer. A
separate white paper on Ayres website details the digital-filter R&D project.
The result is the implementation in the QB-9 of two
user-selectable Minimum Phase alternatives. The first, labeled Measure on the rear panel,
closely follows the apodizing design espoused by Craven and adopted by Meridian in its
808.2 Signature Reference CD player. The second, tagged Listen, features a more gradual
slope that significantly reduces the post-ringing of the filter to about one cycle, albeit
at the expense of a slight rolloff in the uppermost frequency response and a partial loss
of the theoretical benefits of "apodizing" (surmised to eliminate pre-ringing
embedded in digital media during the recording process). As Hansen often notes, there is
no such thing as a free lunch in design, only a balance of tradeoffs, and he feels that
any tradeoffs inherent in the Listen approach are overcome by the enhanced musicality and
naturalness of the sound. Both of Ayres Minimum Phase designs use a one-pass 16x
upsampler rather than the normal cascade of 2x upsamplers, and thereby reduce
significantly the opportunity for compounding rounding errors in the data.
While using a computer to store and manage a large library
of music has become for many the preferred audio "transport," the computer
itself introduces significant barriers to good sound, from switching power supplies that
radiate radio-frequency interference (RFI) through connecting wires (e.g., USB
cables) and power cables (into the AC wiring itself), and dozens of competing clocks of
varying frequency. Hansen is more blunt: "The bottom line is that the last thing you
should do is to hook up a computer to your audio system, but since that is what people are
doing, we do everything possible to minimize or even eliminate the electrical pollution
that a computer inherently creates."
Ayre attacks these problems in two ways. They galvanically
isolate the computers electrical ground (and that of the USB receiver board within
the DAC) from the QB-9s chassis and audio board by the use of high-speed
optocouplers. This keeps RFI from infecting the audio system via the USB cable.
Additionally, the QB-9 uses full-size Ayre Conditioners -- proprietary RFI filters that
absorb RF energy and dissipate it as heat -- to clean up the AC before it enters the
QB-9s transformer, which then employs separate windings for the segregated digital
and analog circuits. Even the "dirty" power drawn by the USB receiver board from
the computer via the USB umbilical is separately cleaned by two micro Ayre Conditioners.
Finally, as a result of technology trickled down from
Ayres R-series components, the QB-9 has a new analog output stage featuring EquiLock
circuit design. In essence, the EquiLock circuit adds a transistor that fixes the
operating point of the actual amplification transistor and holds it steady, allowing it to
operate more linearly and with reduced distortion. While this new output stage relies on
bipolar transistors rather than Toshibas now-discontinued audio-grade FETs -- a move
that necessitated a return to the drawing board -- Hansen claims it has paid off in an
incredible level of performance and "an even greater insight as to what creates the
sound quality that we look to achieve with our designs." As mentioned above, the
positive results attained with this new output circuit have now been incorporated into the
K-5xeMP preamplifier.
System
Given its relatively low price and high aspirations, I
examined the QB-9 in the context of both my primary and secondary systems. In both cases I
used as the source a tricked-out MacBook computer upgraded with 4GB of RAM and
Samsungs 64GB solid-state drive, ran Apples iTunes and/or Sonic Studios
Amarra player software, and a 1TB external hard drive on which Id stored my music as
uncompressed AIFF files. The computer and external drive receive power via an Audience
aR2-T high-resolution power conditioner to isolate computer-generated noise from the audio
system on the power-line side, while the umbilical between computer and QB-9 was the
excellent and affordable Wireworld Starlight USB.
In my secondary system I connected the QB-9 to an Ayre
AX-7e integrated amplifier driving a pair of Avalon Acoustics Mixing Monitor speakers.
Wiring consisted of a Stereovox BAL600 balanced interconnect, an 8 pair of Stereovox
Firebird speaker cables, and a suite of Cardas Golden Reference AC cords. A Billy Bags
I-Beam audio center housed the lot.
When in my main rig, the QB-9 fed, in turn, my Ayre KX-R
line-stage preamplifier, Ayre MX-R monoblock power amplifiers, and Vandersteen 5A
speakers. Wiring consisted of Cardas Clear balanced interconnects and internally biwired
Cardas Clear Beyond speaker cables, along with Cardas Golden Reference AC cords and Ayre
L-5xe passive power conditioners. The MX-R monoblocks, sitting atop custom Harmonic
Resolution Systems M3 platforms, resided next to the speakers to keep the speaker
cables length to no more than 1m, with all other equipment in a custom Billy Bags
rack.
Listening
Ayre equipment favors burn-in time, so the first thing I
did was hook up the QB-9 to a backup computer and log over 250 hours of continuous use. It
must have been sufficient; as soon as I inserted it in my system, the Ayre DAC sounded
fantastic, and I heard no change in its sound thereafter.
Once the QB-9 was ensconced in my system, I hit it with all
nature of music, from the jazz piano in Ahmad Jamals Chamber Music of the New
Jazz (CD, Verve/GRP 268202), which features Jamals groundbreaking use of
silence, space, and surprise, to hip-hop in De La Souls 3 Feet High and Rising
(CD, Tommy Boy/Warner Bros. 01019) -- a veritable cauldron of inventive and deftly layered
rhymes and samples. The QB-9 sorted complex harmonic structures and pacing with aplomb.
With its Minimum Phase filters set to Listen, the time-domain stability was palpable. Free
of pre-ringing, the upper registers sparkled -- definition and musicality happily
coexisted, even with the severe compromises foisted on the music by the "Red
Book" standard.
After favorably sampling a bevy of tracks previously ripped
from my collection of CDs, I moved on to some brand-new releases that exemplify the very
best the CD format has ever offered. A new edition of Stan Getz and Joćo Gilbertos Getz/Gilberto
(Verve/First Impression Music LIMK2HD036) features the 2KHD Mastering process championed
by First Impression Music (FIM). This title is not only one of my standards, its a
favorite of my wifes, so its played frequently here. The ends to which Winston
Mas company goes to reduce the destructive effects inflicted by typical production
processes were justified by what I heard through the QB-9. This album had never sounded so
good. Its sound surpassed that of my SACD copy, and though not as tonally saturated as my
vinyl pressing, this new 2KHD edition removes a certain nasal quality from Astrud
Gilbertos vocals and provides levels of life and three-dimensionality that are
simply startling for a 16/44.1 file.
As good as "Red Book" can sound when
reconstructed in the analog domain by the QB-9, it is only with high-definition music
files that computer audio in general, and the QB-9 in particular, fully shine. Ive
downloaded from iTrax.com 24/96 files of several masterpieces published by the 2L label,
including the Grammy-winning Divertimenti, by the TrondheimSolistene (2L50). This
spectacular recording embodies a refreshingly modern variety of classical orchestral
music. With this truly high-definition file, the characteristics already revealed by the
QB-9 were intensified, and the resulting experience more detailed yet relaxed, engrossing,
and "analog-like."
Another Grammy winner, Alison Krauss and Robert
Plants Raising Sand (Rounder 11661 9075), is available as a 24/96 download
from HDtracks.com. While I found the CD edition enjoyable, I began to understand what all
the fuss was about only when I heard the hi-rez version. The interplay between Krauss and
Plant evoked a newfound electricity, and the bass clearly emanated from particular
instruments rather than an unidentifiable bass machine. HDtracks promises over 1000 titles
available in 24/96 by the end of 2009, ensuring dozens of quality performances to suit any
taste. The future sounds brilliant.
So, too, I reveled in the 24/192 master-file quality of
Kent Poons Audiophile Jazz Prologue III (Design w Sound DWS-8001), as well as
multiple HRx titles from Reference Recordings, each a bit-perfect copy of one of Prof.
Keith O. Johnsons 24/176.4 master files. Given the current limitation in bandwidth,
playback of these titles required downsampling to 24/96 and 24/88.2, respectively, but the
vast majority of these hi-def files splendor remained. Such downconversions will
soon be things of the past, as the previously mentioned 24/192 (and 24/176.4) receiver
board will become standard on the QB-9 in a few months time, and will be available
as an upgrade for all original-spec QB-9s for less than 10% of the retail price of a new
QB-9. Who said you cant have your cake and eat it, too?
A high-performance shakeout
To validate the QB-9 as the current state of the art, I
compared its performance with that of my C-5xeMP player ($5950) and Wavelength
Crimson USB DAC (from $7500). I also reflected on what I heard in summer 2008, when I
listened to a Wavelength Cosecant v3 and a Weiss Minerva DAC ($4500). At that time, I
concluded that "Red Book" data played through the Minerva all but equaled the
quality from corresponding CDs played through my C-5xe (pre-MP upgrade). However, in my
secondary system, I noted a preference for the Wavelength over both solid-state units.
While not quite as neutral or extended, the Cosecant had a beguiling midrange purity, and
with many recordings was more forgiving in the upper registers (the Avalon Mixing Monitors
can be brutally revealing).
I subsequently purchased Wavelengths top-of-the-line
Crimson, which can be customized balanced or single-ended, with copper or silver
transformers, and with one of three alternative DAC modules. Thereafter the Crimson did
nearly universal service in my Avalon system, relegating my Ayre C-5xe to primarily SACD
duty. (Sadly, SACD and computer audio dont mix.) The C-5xe found new life, however,
with the upgrade to MP status and the Minimum Phase filters, which provided startling
sonic gains -- the Listen setting is my preference. Consistent with what I then heard
through the QB-9, a veil was lifted in the midrange with the MP filters in place, but the
real advances were audible on top -- massed strings lost their congestion, cymbals their
sting (the pre-ringing imposed by linear digital filters could be the culprit behind the
artificial "edge enhancement" that both distracts and fatigues with 16/44.1).
With "Red Book" sources, the C-5xeMP proves the predominant winner,
although the Crimson continues to offer greater convenience in accessing files, provides
exceptional playback of downloaded 24/96 content, and nevertheless remains my preference
for certain recordings.
Now for the shakeout. When compared head-to-head with the
C-5xeMP, the QB-9 was, however narrowly, the consistent winner with "Red
Book" material. That preference became even more marked when I used Amarra, which
provides positive results with nearly every album I sample (though its benefits are most
pronounced with CDs released in the 1980s and early 90s). There will always be those
who prefer the single-chassis plugnplay CD player to computer audio, but for
those who decide to go the latter route, a C-5xeMP or other cutting-edge disc
spinner in the same system is simply redundant unless you have a significant collection of
titles on SACD. Extrapolating to the Minerva, whose sound didnt quite equal the old
C-5xes, the QB-9 reigned sonically superior. Keep in mind, however, that the QB-9 is
a dedicated USB DAC, while the Minerva possesses "digital hub" flexibility due
to its dual S/PDIF inputs (AES/EBU and RCA) in addition to its FireWire link to a
computer.
Comparisons with the Crimson offered interesting contrasts.
When optimized in my systems, the QB-9 bested the results of the tubed DAC, but the
Wavelength nevertheless expressed a beguiling midrange purity and a more forgiving nature
that many suitors will prefer. To obtain optimal sound quality from the QB-9, it needs to
be supplied a native-rate datastream, as it proved far more sensitive to upstream
variables and preprocessing in the computer.
Using iTunes, native-rate playback can be a real pain
because it requires manual switching of output datastreams (e.g., from the
"Red Book" frequency of 44.1kHz to a hi-rez frequency of 96kHz), through the
process of closing iTunes, opening the Audio MIDI settings, changing the output frequency
to any new "native rate," closing Audio MIDI, and reopening iTunes. This becomes
especially annoying as music-file libraries grow more varied with the ever-expanding
availability of hi-rez content. (Amarra addresses this iTunes limitation by featuring
native-rate auto-switching.)
With the Wavelength Crimson, my practice was to leave the
output setting at 88.2kHz and let the computer simply double the "Red Book"
frequency, halve any 24/176.4kHz files, and otherwise perform an asynchronous sample-rate
conversion for 24/96 and 24/192 data. With the QB-9, however, a clearly perceptible
deterioration in performance occurred with such a set-it-and-forget-it approach, since
only two of my 1200 albums are stored as native 24/88.2 files. When I pointed this out to
Hansen, he acknowledged that upstream sample-rate conversion in the computer (which is
tantamount to inserting another digital filter) can significantly degrade the sound. As a
result, and until the arrival of Amarras auto-switching, I was forced to set the
Audio MIDI output at 44.1kHz to accommodate the vast majority of my audio files, sourced
mostly from CDs. To manually change the output setting to 24/96 to critically listen to
files downloaded from iTrax and HDtracks is an extra and nontrivial step that places the
QB-9 behind the Crimson in terms of convenience -- a primary part of the attraction of
computer audio in the first place.
The Crimson was also less sensitive to changes in USB
cables. One of the biggest differences between USB cables seems to be their effectiveness
at limiting the transmission of RFI along the ground, and in the shielding of
power-delivery conductors. (A USB cable has multiple signal conductors, plus one that
transmits power from the computer to auxiliary devices.) With the QB-9, Wireworlds
Starlight USB improves on their Ultraviolet USB, which in turn is an improvement over my
older Kimber USB and Belkin USB2 Gold. To effectuate its ground-isolation scheme, the USB
receiver board in the QB-9 relies on power via the USB cable, while the Crimson draws no
power at all from the computer. Note, too, that tube-based systems, with their
transformer-coupled inputs and outputs, seem more immune to the performance-robbing
affects of RFI, which may account for their resurgence in the high end. Given the
RFI-radiating engine that is a computer, the transformer-coupled Crimson employs a
topology with some inherent advantages. Such distinctions may explain the differentiation.
Accordingly, depending on the nature of the system and the users preferences, the
Crimsons attributes may offer a superior balance, albeit at a significantly higher
cost.
Watershed moment
My time with the Ayre QB-9 amplified my certainty that
computer-based audio is not only the future, it is the here and now. Providing
significantly greater performance than any similarly or lower-priced alternative, and
undoubtedly one of the best computer-audio DACs now available regardless of price, the
QB-9 is a watershed component in this watershed year. It is what it is, nothing more,
nothing less: a USB DAC unabashedly focused on making the best possible computer-audio
sound for the least amount of money.
A certain irony must be at play in the Ayre Acoustics
universe. Hot on the heels of the KX-R line stage -- Ayres most expensive product
and, in my opinion, its most sophisticated, musical, and aesthetically refined -- the QB-9
is not only Ayres least expensive product, but its equally
ground-breaking, and probably more significant to the world of high-performance audio at
large. Whereas the KX-R will grace mere hundreds of systems, Im sure that many
thousands of QB-9s will soon be enhancing the lives of many thousands of computer
audiophiles.
. . . Peter Roth
peter@ultraaudio.com
Ayre Acoustics QB-9 USB Digital-to-Analog Converter
Price: $2500 USD.
Warranty: Five years parts and labor.
Ayre Acoustics, Inc.
2300-B Central Avenue
Boulder, CO 80301
Phone: (303) 442-7300
Website: www.ayre.com
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