Early this year I fell though
the rabbit hole into the wonderland that is high-end computer audio. More
precisely, it was a calculated move designed to take advantage of a maturing
technology that in the span of just a few years sprouted from infancy to a
relatively mature state. The incentive was far more than just a matter of
convenience, of being able to manipulate hundreds of music files without
rummaging through a pile of physical media. It was about access to high
resolution 192kHz/24-bit and 92kHz/24-bit music files, available for download
for example from HDtracks.com. But also the realization that standard CD quality
files, that is 44.1kHz/16-bit data played back off a computer, can potentially
be reproduced with less jitter and greater fidelity relative to what even an
expensive CD player or transport is capable of. Now that was more than incentive
enough for me to embrace computer audio.
The core of my computer audio system consists of
a Mac BookPro laptop with 8GB of memory and a solid-state hard drive running
Sonic Studio's Amarra Version 2.5 music player software. From my perspective,
Amarra's support for up to 384 kHz sample rates, memory cache playback, and
playlist mode make it a clear winner. Of course it integrates perfectly with
Apple's iTunes, but it can also operate free of iTunes in play list mode. The
next order of business was to integrate computer file streaming from the Mac's
USB 2.0 port with an external DAC or CD player digital input. It turns out that
not all CD players or DACs possess a USB input and those that do may well not
offer an asynchronous USB input. What is an asynchronous input you ask? In a
nutshell, it's an input that incorporates a clock for controlling the incoming
data stream. Rather than allowing the Mac's internal clock to control the data
stream, the Amarra software makes it possible for an external low-jitter clock
to take control. After all, a computer's primary mission in life is not to
generate a stable clock. And proximity to switching power supplies, CPU, and
other digital noise sources could compromise the internal clock's performance.
The idea then is to avoid using your PC's soundcard or Mac's onboard DAC. And
that's where April Music's Stello U3 comes in.
The U3 is natively supported by the Mac OS X, so no driver installation was necessary. However, the U3 is bundled with a driver installation CD for Windows OS. An AudioQuest Carbon, 1.5-meter length USB cable, was used to connect the Mac BookPro to the U3. A 1-meter coaxial cable was used to connect the U3 to an external DAC's SPDIF input. From the Amarra file pull-down menu, one can open the Audio Device Preferences window and re-scan audio devices to recognize the U3. The final step in managing the connection is to select the U3 (identified as XMOS) as the output port.
Differences between these two modes of file playback were dramatic, the sort of night and day differences worth writing home about. Let me first of all make clear that sonically the EAR DAC is one of the best money can buy. In my experience, a tube output stage is an important criterion for the success of failure of a given DAC. Getting tubes into the digital front seems to civilize harmonic textures and intensify tonal colors. No matter how good the DAC chipset is and how low-jitter the digital to analog conversion might be, I can still plainly identify the differences between solid-state and tube buffer stages. I've been a proponent of tubes in DACs for many years, as this in itself seems to be responsible for much of the sonic differences between DACs. One of the advantages of a vacuum tube output stage, as is the case with the EAR DAC, is its inherent spatial integrity. The ability to flesh image outlines with genuine palpability and to portray a soundstage with convincing depth perspective and lateral extension have been and will likely remain the domain of the vacuum tube.
For the past several years I've been using a
ModWright modified Sony XA-5400ES SACD player as a reference digital front end.
Using the Sony as a transport allowed me to compare computer files ripped onto
the Mac to the same CD's digital feed from the Sony SACD player's digital
output. The findings were quite startling, especially since I didn't expect much
of a difference. But for the record, the computer file playback resulted in
enhanced microdynamic shadings, purer textures, and an increased sense of
transient clarity. However, comparing the ModWright Sony's analog output to that
of the Mac+U3+EAR DAC gave a much closer sonic score card. So in the final
analysis, file playback though the U3 easily bested the performance of the Sony
as a transport. And not only that. I've auditioned a $20K+ transport in the past
couple of years and I would venture to say that I could live happily ever after
with the Mac and Stello U3 combo even in the face of such pricey ultra-high-end