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AudioEngine D2 Review (Linux Audiophile)

From: andrew cooke <andrew@...>

Date: Sat, 10 Nov 2012 10:17:45 -0300

The short version: works great.

More details than you could possibly want, plus some small negatives follow.


Background

As I explained at http://acooke.org/cute/LinuxAudio0.html I am looking for a
replacement for Logitech Squeeze devices.  I used a Duet to stream music over
wifi from my computer to my hifi, but the hardware is no longer supported and
the software is broken on the latest OpenSuse.

I chose the AudioEngine D2 because (1) I owned a D1 and liked it and (2) I
felt that a hardware-based approach would be more future-proof.  This is a
review of the D2.


Physical Appearance

The D2 is two boxes, and both are larger (wider and deeper) than the D1.  One
box connects to the computer as a USB (or optical) soundcard, which sends the
signal to the other over wifi.  The second box has digital and audio output to
connect to the hifi.

They look fine, but compared to the D1 have some downsides:

 - The D1 feels heavier for its size, and so more solid.

 - The D1 has controls at the front and terminals at the back.  Both
   D2 boxes have all connections (including power) on the front panel.
   Only the wifi antennae are on the back.


Initial Impressions

My hardware are ex-demo (the last pair available in Chile, I think), but they
appear to be in good condition.

When I first connected them (without reading any instructions) everything just
worked.  No problems.  In particular, the D2 works immediately when connected
as a USB device to Ubuntu 12.10 (although all listening was done via a V-Link
- see below).

But later, when I connected the digital out to my Audio GD NFB 3.1, I could
only hear white noise.  This was very worrying and took me a while to
understand - it turned out the NFB 3.1 was configured to use 8x oversampling,
which was limited to 48 kHz signals, while the D2 emits a 96 kHz signal.
Switching to 4x oversampling on the NFB 3.1 fixed things, but I have no idea
if you can also change the D2 output (I don't see how, but I have never
worried much about these things).

The wifi range seems fine.  Part of the deal with me buying the demo hardware
was that I could return it if the wifi range didn't reach across my apartment
(that may sound odd to American ears, but in Chile is reasonable customer
service!) - it has worked with no issues at all.


Some Background on Listening

I will describe how the D2 sounds with various combinations of amplifiers and
speakers, and compare it with other DACs.  I don't have the ears and / or
audio memory to describe things in absolute terms, but hopefully a collection
of comparisons will be as informative.

My music is MP3s, 192-320 or good quality VBR.  That may effect some of what I
hear, but many of my comments will be comparative, and so should not be
affected in the same way.  For example, my general concern about a harsh
treble in my office my be partly blamed on MP3s (although I suspect hard,
reflecting surfaces on either side of the room), but if I say that one DAC has
more treble than another, then that should be true for any source (lossless or
not).

The signal used for all DACs comes via a Music Fidelity V-Link.  This is a
USB-to-optical converter that provides a buffer and separate clock.  So the
digital signal fed to the DAC should be better quality (less jitter) than what
is available over USB directly from the computer (in all honesty, I have never
heard a difference, but the theory makes sense).

Apart from a few favourite tracks, I will be listening to whatever turns up on
shuffle, so forgive the occasional obscure reference...

Finally, note that with the optical output, the D2 can be used as a purely
digital cable (which you then connect to your favourite sounding DAC), which
should have no (or very little) effect on the final sound.


Office: D1 v D2 with BW 602, Cyrus One

This is where I work, with BW's large, wall mounted monitors either side of my
desk.  The acoustics aren't great (glass on one side, cupboard doors on the
other) and the BWs don't have the smoothest midrange, so I've been using the
D1 through an old Mission Cyrus One amp, hardwired to skip the (noisy, broken)
preamp.  The D1's restricted treble gives a less tiring sound than listening
to the NFB 3.1 through wire from the living room.

To simplify A/B switching, the digital signal here is always going through the
D2 (whose optical out is connected to the D1).  In this way I can simply
alternate between the line outs of the D1 and D2.

First track - Spearhead's Chocolate Super Highway - it's clear that there's a
different tonal balance between the two because I can't find a single volume
level to compare them.  If I match the bass, the D2's treble is noticeably
more prominent.

This is good news - the D1 is bass-heavy (see my earlier comments at
http://acooke.org/cute/DACReviews0.html), so the D2 may well have a flatter
response.

More careful listening with the start of Horace Silver's Sister Sadie,
comparing the cymbals and trumpet, suggests that the D2 mid and highs are more
even; the trumpet on the D1 is more pronounced.  With an acoustic track, like
Graveyard by Forest, the D2 has more a little more "sparkle" - you can more
easily hear the little details from the guitar strings rubbing against frets,
etc.

On The Necks' Sex the D2 seems to have slightly more ambience.  I am not sure
what I am hearing, and may be imagining things, but it sounds more open.
Perhaps the extended treble compared to the D1 is improving stereo imaging?

I think there is also more extension in the bass with the D2.  There is some
evidence on Ted Poor's Sundae #3, where the bass seems to be fatter, more
rounded.  And in Max Richter's Shadow Journal the "thunder" appears to have
more structure and detail.  But it's not something I'd swear by.

So, in short, the D2 appears to be more extended, particularly in the treble,
than the D1.  In my particular context, with the poor acoustics here, I don't
know whether this is good or bad.  That will take a lot more listening, to see
whether the D2 becomes tiring.  Although a direct comparison with the NFB 3.1
could help, too.

But The Necks sound good on either.  Love that band.  :o)


Living Room: D2 v NFB3.1 with Quad 12l, Arcam Solo

These speakers are much more civilised, with a very smooth midrange, but less
extension than the 602s - a much more laid-back sound.

And it's very difficult to hear much difference between the D2 and the NFB
3.1 (apart from an annoying difference in level that makes A/B switching
slower than I would like).

Listening to Bowery Electric's Inside Out, again and again, I managed to
convince myself that the NFB 3.1 better separates the different instruments,
perhaps because it's slightly richer in the midrange.  The best way to
describe the difference is that the NFB 3.1 sound like the volume is a touch
higher (if you've ever compared audio components you'll probably have thought
one thing sounded better than another, only to realise later that it was
playing slightly louder - that kind of general "oomph" is what I am hearing to
the advantage of the NFB 3.1, even though the levels are, I believe, matched),

But it's subtle, and I am not at all sure it's for real.

And on the next track I listen to - Violent Femmes' Good Feeling - I think I'm
favouring the D2.  Argh.  There really is nothing in it.  They seem equally
good.  I suspect they are both more-or-less flat - just decently engineered
DACs, doing their thing.

Later, I switched the NFB 3.1 for the Music Fidelity V-DAC, which has a little
less in the mid-range.  Here, I felt the D2 sounded better, but again the
difference was marginal - on Amo Chip's Respite the piano had a bit more bite,
and was more cleanly separated from the bass (amusingly, I initially wrote the
above reversed, preferring the V-DAC, but then found my cables / inputs were
not arranged as I had assumed, leading me to confuse the two).


Comparison with Logitech Duet

Since my Duet is currently dead I cannot directly compare sound quality.  But
I bought the NFB 3.1 because I was unhappy with the Duet, and the NFB 3.1
sounds similar to the D2 (see above).  So presumably the D2 sounds better than
the Duet.

Anyway, what I can compare here is functionality.  The Logitech and
AudioEngine solutions do quite different things.

The AudioEngine D2 is "hardware only".  It provides a "wifi digital cable", a
good sounding DAC, and a remote volume control.  They all work out of the box.

The Logitech solution is more complex, because it includes a substantial
software component - the media server.  So the Logitech solution also provides
a way to manage and play your music.

As far as I can tell, the D2 wifi performance is at least as good as the Duet
- it has worked with no issues at all (not one drop-out) across a larger
distance (with more walls) than the Duet.  On the other hand, the Duet
connected to any wifi hub, while the D2 must connect to the base unit, which
in turn is connected to the host computer by USB cable.

One way to compare the two, then, is to say that Logitech gives you more - it
has all the functionality of the D2, plus the extra flexibility that comes
from the software.

On the other hand, once the software dies, the Logitech hardware is useless.
In contrast, the AudioEngine solution will last as long as the hardware.  And
in my experience (as a software engineer!) hardware is more reliable than
software.

Finally, I believe the AudioEngine D2 has better sound quality - I needed to
replace my Duet DAC with the NFB 3.1, and the headphone out on my Boom (the
two-speaker radio Logitech produced) was so noisy it was unusable (which meant
I almost never used it, since my main need was to listen on headphones when I
couldn't sleep - speakers are no good when someone else is asleep next to
you).


Conclusions

- The D2 works perfectly as a simple, digital bridge.  You can connect a
  digital signal to one box, send it over wifi, and have it emerge from the
  other box.  The input can be USB or optical; the digital output is optical.

- The digital output appears to be 96kHz, which caused (temporary) problems
  with a DAC configured such that it was limited to 48kHz input.  You may want
  to check older DACs for compatability (or it may be that this can be
  controlled by sending a lower-frequency signal - I really do not understand
  the technical details and am simply flagging it as a possible issue).

- I had no problems (beyond those common to all sound devices) using the D2
  from Linux.

- The D2 can also be used as a DAC, generating a line level signal for your
  amplifier.  The DAC sounds good - similar to my NFB 3.1, which is, I think,
  recognised as a decent "budget audiophile" DAC with a neutral sound.

- When used as a DAC, the output level can be adjusted using a volume control
  on the box near the computer.  Since the DAC is good quality this is a
  useful feature - you can adjust the volume from your computer without
  compromising quality (the adjustment is made to the analogue signal).

- The main negatives are: no headphone port (although this makes some sense as
  there is no volume control on the "receiver" box); all ports on the front
  panel; not as solid-feeling as the D1.

- A D2 is not the same as a Logitech device.  In some ways it is better, in
  some ways worse.  But for me, it is a good replacement for a Duet.

- Value for money?  As a wifi-bridge only, the D2 is expensive.  But if you
  include the DAC, which sounds good (and neutral), then it makes more sense.
  The boxes don't feel as solid as the D1, but they seem to be well made.

http://audioengineusa.com/Store/Audioengine-D2
http://www.audio-gd.com/Pro/dac/NFB3-2011/NFB3.1EN.htm

Andrew

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