Precision Tools for Audio Professionals

In these Application and Installation Notes we will go over the IMPORTANT details that you'll need to remember to let the computer work happily with the ARX Audibox USB series.

The ARX Audibox USB series of devices are true Plug-and-Play Digital/Analog audio interfaces, using the popular Universal Serial Bus connector found on computers - a digital version of the analog audio Direct Injection (DI), or Direct box.

Depending on how your computer is set up, the USB-DI will usually automatically install itself as the default audio device as soon as it is plugged in. If not, you'll have to choose it from the above-mentioned list.

To be able to do this, the USB-DI uses the generic USB audio drivers built in to the operating system. And like everything in life, there are rules built in to this generic driver which have to be followed

Rule # 1
The USB port that you use on the host computer must be used for the USB-DI only.

Rule # 2
Don't plug the USB-DI into a hub unless you want additional noise from other devices plugged into the same hub.
However - If you are using a laptop with only 1 USB connector and have to use a hub, then check all the ports on the hub to find the quietest one, and be very careful when using other USB devices connected to the hub at the same time.

Rule # 3
You can only use ONE installed audio device at a time. If you plug in a USB-DI, the computer will assume you want to use it and stop using the previous audio device if there was one - for example, the computer's inbuilt audio card.

If you unplug the USB-DI, the previous audio device will be available again, although you may have to re-select it from the list of Audio Devices. Go to Control Panel/Sounds and Audio Devices/ and click the list of Sound Playback and Sound Recording Devices

Rule # 4
We recommend you use either the USB cable supplied, or one less than 4 metres (~12 feet) long

There are also some Important Details below which reinforce these rules:

Please Note: For detailed information on Windows XP and later operating systems, please follow the links at the bottom of this page.

The Windows default volume setting for USB Audio Devices is 50% of maximum. For our purposes this will be too low, inducing noise and hum as excessive gain may need to be applied to deliver the level required.

We recommend increasing this volume setting to 100%, on both PCs and Macs.

No matter which operating system you are using, once the USB-DI is installed, go to Control Panel, then Sounds and Audio Devices, then USB Audio Device, then the Volume tab, and move the slider to the right.

This will give you the optimum signal to noise ratio.
<<< See panel at left

NOTE: This still needs to be done even if you are using the USB DI-VC model. The volume control only affects the analog outputs, and you'll need to increase the digital volume first.

NOTE 2: This may need to be done each time you plug the USB-unit in after removing it, depending on the operating system

IMPORTANT DETAIL # 2

Laptops and Power
If you are using a laptop/notebook computer with the Audibox USB-DI / USB DI-VC / USB I/O, we strongly recommend that where possible you run the computer from its battery - fully charged, of course!
We have done extensive research on grounding and signal isolating techniques on our USB series of products, and have incorporated all of it into their design.
While it may be more convenient to run a laptop from its external power supply, the sad truth is that not all external power supplies are created equal; in fact many of them are just not up to the standard required for any kind of audio.

Many often come with the surprise addition of a pink noise, digital noise and hum generator built in, a feature which unfortunately cannot be disabled!

Price and brand also have very little bearing on the quality of the laptop power supply! It's a very good idea to carefully check your laptop and power supply combination prior to any kind of audio use, and if in doubt, stay with the battery.

Another alternative is one of the aftermarket generic power supplies, as sold by many computer shops. However, try before you buy is the name of the game!

Desktop Computers and Power
The Grounding layout of Desktop PCs, Macs and their Power Supplies is also sadly not one of life's great constants, as they all feature widely varying grounding arrangements. To compensate for this, and to assure you of the lowest possible system signal to noise ratio, we've fitted the whole USB Series with a Soft Ground lift switch that allows connection or isolation between your Computer's ground, and the grounding pin 1 on the units XLR connectors. Simply select the setting, in or out, that removes any audible hum when using your Computer USB DI or I/O combination.

Stay Alive!
And remember, never ever remove, snap or cut off the Safety Earth pin on any Power Lead associated with your Computer, its Power Supply or any of your Audio Equipment, as this could expose you and those around you to a potentially fatal risk of electric shock.
If after switching your USB unit's ground lift switch in and out and comparing hum levels your system is still noisy, consult a Technician as your problem lies elsewhere.

IMPORTANT DETAIL # 3

Computers are very electrically noisy environments, and USB is a very popular Plug and Play protocol for lots of Windows devices. It's quite likely that you will already have various USB devices in use on your computer.

For fastest and quietest audio operation you must plug the USB-DI / USB DI-VC into its own USB port. Experiment on your computer to find the quietest USB port, and keep it only for the USB-DI - don't have anything else on the same buss. So don't plug it in to a spare port on a 4 or 6 way hub that you have connected to the computer!

Otherwise you may get a hissing and clicking noise every time you move the mouse, touch the keyboard, or click on the screen.

IMPORTANT DETAIL # 4

Keep mobile/cellular phones well away (at least 2 metres/8 feet) from a computer when using it for audio. The "Dut-dut-dah-dut dut-dah-dut dut-dah-dut" sound of a mobile phone changing cells or connecting is not one that many audiences care to hear!

IMPORTANT DETAIL # 5

Audibox USB units contain multiple transformers, double shielded for ultra low noise. However, they are still transformers, and as such they are always looking for something electrical to transform! Do not sit any of your USB devices on top of an amplifier, as these can spray out Radio Frequency (RF) interference, digital 'zipper' noise, hum and buzz inducing noise in large amounts that may force their way into the transformers inside the USB devices. Keep them as far away as necessary to avoid this happening.