DI boxes. They’re (usually) quite simple yet crucial devices that convert an
unbalanced high-impedance signal from, say, a guitar or a keyboard to a balanced
low-impedance microphone-level signal.
There are a few reasons for this, but the main purpose is to make sure an
unbalanced, high-impedance signal doesn’t pick up noise on its way to the preamp,
particularly over long distances such as over a mic snake. The result of running an
unbalanced signal that doesn’t match the input impedance of your balanced preamp
will have other trade-offs, such as less signal level (usually around a drop in 6dB)
and an altered frequency response, usually manifesting in a top end roll off.
Second, it enables a line level signal’s gain to be controlled via the microphone gain
pot, which usually offers a lot more gain to work with.
So that’s the basic idea; a DI box maintains balanced signal integrity from an
unbalanced, high-impedance signal for insertion into a microphone preamp.
Now, you may have noticed that I included the exception “usually’ in brackets in the
second sentence of this article. The reason for this is because there are companies
out there doing some very interesting things with DI boxes and one of those
companies is ARX, the Melbourne, Australia-based company that manufactures
“precision tools for audio professionals’.
I was lent an ARX Audi-box Blue DI by local ARX distributors Matrix Sound, and this
little guy is refreshingly different. Aimed at corporate, DJ and other work where the
main source of playback content is hosted on a Bluetooth-enabled smart phone, MP3
player or laptop, this handy tool allows wireless playback in stereo over the
protocol to a claimed radius of 12m. That could be quite handy, so let’s take a
The Audi-box Blue is, well, blue. Matte-royal blue, in fact, and while light in weight,
the all-steel housing feels well-made and robust. It’s got a roughly 2cm wide, grippy
foam footing that squares the entire perimeter of the base too, which ensures it
doesn’t go anywhere when placed on a flat surface.
The rest of the features are quite straight-forward, really. It’s got two balanced
male XLR jacks on the one end which are the left and right stereo outputs of the
device along with a power on/off button. The output impedance is 200 Ohms so the
XLR outputs should pair well with most microphone inputs on common consoles and
preamps. Since the source signal is fed via Bluetooth, the output gain is nominally
at unity with the source device.
Of course, like most DI boxes, this one can also run on 48V phantom power which is
fed to the device via the output XLRs coming from the preamp. However, both
channels being fed from the DI need to have phantom power enabled in order for
the device to power itself. If phantom power is not available, there is a +12VDC
socket for an external power adapter (not included).
On the opposite end of the Audi-box Blue there are two LED lights arranged
vertically – a blue one on the top and a red one below – that indicated when the
device is scanning the airwaves (red) or when there is Bluetooth activity (blue).
When the device is communicating with a source device the blue LED will blink and
when the device is successfully paired and locked, it will remain solid blue.
However, if there is a problem during pairing to the right of the LEDs there is a red,
non-latching button that resets the device back into scan mode for another attempt.
That’s about it. It really is that simple.
In this test I decided to attempt to pair all my available Bluetooth-enabled devices
with audio playback, one at a time, to the Blue DI. These devices included my
iPhone, my iPad and my PC Laptop.
I plugged the outputs of the DI into two available inputs (channels 7 and 8) of the
ART Tubefire 8 I use in my home studio and enabled phantom power. The analogue
outputs of the two channels were then fed into an Apogee AD8000, running at 24-
bit, 44.1kHz which then digitised the signal and was routed back out via AES/EBU to
my Dangerous Audio D-Box monitor controller and eventually on to my Yamaha
HS50 studio monitors. Essentially what I ended up with is a simple, modular digital
The first device I tried to pair was my iPhone. The scan light was blinking on the
Audi-box and as soon as I enabled Bluetooth on my phone the blue light started
flashing to show Bluetooth activity. I selected the “ARX Blue DI’ in the iOS Bluetooth
settings and voila, the blue light went solid, showing a locked and steady
connection. At this point I would like to add, that while I tried the iPad third, it had
the exact same result and was just as easy to set up. So, as far as I could tell, iOS
devices work flawlessly with this unit.
I played some music off of Youtube and some high quality files from Billy Joel and
AC/DC through the Blue DI and the quality was surprisingly good. I have only ever
used Bluetooth to share files and once upon a time with a hands free kit and didn’t
recall the audio quality being too stellar. However on this occasion through the Blue
DI, it sounded very representative of the source. I switched my headphones
between listening directly from the iPhone/iPad and the monitor controller being fed
from the DI and the difference was negligible.
The PC Laptop was a different story. At first I could only get the PC to see the Blue
DI and pair with it albeit with no Bluetooth services. The ARX Blue DI icon in the
Devices and Printers applet was opaque and greyed out. The blue light on the DI
would not lock, either. Nor did it flash. The red scan light just continued to blink.
Eventually I downloaded the latest Bluetooth drivers for my laptop, installed them
and the computer instantly saw the DI with all available audio streaming services
available. All that was left to do was select the DI as the default audio output and I
was getting a stream.
But this is where it got puzzling. The stream from the laptop was slightly more
distorted in the top end and sounded a bit grainier. I’m not sure if this was a
software problem on the laptop side or whether there was something wrong with
the Bluetooth link, but I couldn’t get it to resolve, despite attenuating the volume on
the PC side. That being said, it could always be a problem with my laptop and not
the Blue DI.
I also tested the range of the unit. I found out very quickly that it does not transmit
through walls, which is expected. I left my studio, walked around the house until I
got a line of sight through window and sure enough, the audio returned. I walked
back several meters (I don’t have a 12m range from my studio window to the
boundary wall) but I would say I got clear transmission for at least seven or eight
meters, which is good enough for most cases.
The ARX Audi-box Blue DI is a handy unit. If I had one gripe I would have liked to
see the addition of an output pad for those instances where you have a low-
headroom preamp but I suppose in that case you could just turn down the volume
on your device. However, all in all, I think this is a very useful tool to have if you’re
a DJ or do a lot of corporate work and the Bluetooth facility just makes it so slick
and fun to use. Welcome to the 21st century where cables are slowly becoming