home entertainment 2007

seemed insurmountable. Would audiophiles
want to spend the time required
to rip their favorite tracks to a computer’s
hard drive? And wouldn’t a drive
large enough to hold high-definition
audio files be prohibitively expensive?
Only three years later, Hyman’s
dream has materialized. Hard-drive storage
capacity per price point has jumped
almost a hundredfold. Gracenote has
become the international leader in digital
media technology and services, providing
complete management systems
for digital media. There has been explosive
growth in the number of online
music vendors—iTunes.com, Rhapsody.
com, Urge.com, and Napster.com, to
name a few—that sell or rent downloadable
music to music lovers.
MEASUREMENTS
To measure the Roku SoundBridge M1001, my original
plan was to use it to access the uncompressed
test-tone data files residing in the iTunes library on
the Mac mini that acts as my household music
server. Unfortunately, while the Roku recognized the existence
of both the library and the SlimServer software that
feeds the library to my Squeezebox, I kept getting a “SERVER
NOT RESPONDING” error message when I tried to browse that
library. I checked that the Mac’s Network, Firewall, and
Music Sharing settings were correct, but to no avail, so I
ended up installing iTunes for Windows on my test lab’s
PC and using that, which the SoundBridge had no problem
accessing.
The Roku’s analog output level into 100k ohms with its
volume control set to “100%” was 813mV RMS, which is a
little lower than the 1V (2.83V peak–peak) specified. The
player did preserve absolute polarity; ie, was non-inverting.
The output impedance at midrange and high frequencies
was relatively high, at 1k ohm. This in itself will not
lead to problems. However, the impedance rose to an
extreme 11k ohms at 20Hz, meaning that the Roku’s bass
will sound rolled-off from its analog output unless it is
Fig.1 Roku SoundBridge M1001, frequency response at –12dBFS into 100k
ohms (right channel dashed, 0.5dB/vertical div.).
Reflecting this sea change in music
distribution, John Atkinson recently
reviewed three network music players:
the Apple Airport Express WiFi
Hub ($129, May 2005, Vol.28 No.5),
the Slim Devices Squeezebox ($299,
September 2006, Vol.29 No.9), and
the Sonos ZP80 Bundle ($999, October
2006, Vol.29 No.10). First, he
centralized his extensive home
library of digital music recordings on
a Mac mini’s hard drive, then wirelessly
distributed digital music files to
different rooms in his house over his
wireless local area network (WiFi
LAN). He could then use each player
to wirelessly direct the streaming digital
files from his hard drive to his
high-end music system via a Mark
Levinson No.30.6 D/A converter.
John found the sound first-rate—he
had to listen intently to hear any
meaningful sonic differences between
the networked music player’s digital
output fed to the outboard DAC and
the digital output of an expensive CD
player playing the original CD and
feeding the same DAC.
Which brings me to the Roku
SoundBridge M1001 network music
player ($199.99). The SoundBridge can
play downloaded music files that are
protected by licensing software—
Microsoft’s Digital Rights Management
(DRM), v.10, using Windows’ Plays for
Sure protocol. This seemed an excellent
reason for me to buy a SoundBridge to
play my own digital files.
used with a preamp having an unusually high input
impedance of 100k ohms or more. Even though there is
still a slight low-bass rolloff into 100k ohms, of –1dB at
18Hz (fig.1), this probably won’t be audible. Of more
interest in this graph is the slight response ripple evident
in the midrange and treble, which implies that the Sound-
Bridge uses a rather old-fashioned digital filter. Channel
separation (not shown) was better than 85dB in both
directions below 1kHz, but decreased to 60dB at 20kHz,
which is still adequate.
My primary test to examine a DAC’s resolution is to
sweep a 1 ⁄3-octave bandpass filter down from 20kHz to
20Hz while the DAC decodes data representing a dithered
1kHz tone at –90dBFS. I initially had a problem in that the
SoundBridge seemed very sensitive to picking up hum
fields from other audio components. I had to place it well
away from everything else in order to be sure that the
results I measured from its analog outputs truly reflected
its intrinsic performance. That performance was puzzling:
the 1kHz tone was reproduced with a large positive error
and a significant amount of second-harmonic content
Fig.2 Roku SoundBridge M1001, 1 ⁄3-octave spectrum with noise and spuriae
of dithered 1kHz tone at –90dBFS, 16-bit data (right channel
dashed).
68 www.Stereophile.com, May 2007