The USB tunnel 24/96 is a digital to digital converter. It is designed to be used
as an interface between a USB port on a computer and an external Digital to Analog
Converter (DAC). The USB Tunnel is capable of handling up to 24 bits 96 Khz, ideal
for high resolution audio. Regular CD quality 16/44 signal also works with the USB
The USB Tunnel is a true plug and play design. Once it is plugged into a USB port
of a computer the computer automatically regonizes the USB Tunnel as the interface
for music to the external DAC. The volume can be controlled by the volume control
in the computer. This is a very useful feature when using the computer as the only
source of the system because the system volume can be controlled from the computer.
That eliminates the need for an additional volume control.
Output: SPDIF (RCA) and AES/EBU digital (standard)
Optional output: Toslink, BNC
All digital outputs have signal present simultaneously
Proprietary firmware design for highest quality signal transfer
Galvanic isolation for low noise operation
Using power from the USB port eliminates the need for an additional power supply
Durable ABS construction
Dimensions: 3.5" long x 2.5" diameter
Weight: 1 lb
Useful Connection Tips
The USB Tunnel accepts the following frequency rates: 44.1k 48k and 96k. (It will
not accept 176.4k and 192k)
Connecting the USB Cable
When you connect the USB cable from the USB Tunnel to the Computer, the computer
will take a while to load the driver automatically. Once the computer has loaded
the driver, the computer will now have an audio device named "Blue Circle Audio USB".
It is also labeled as a SPDIF interface.
USB Settings (Vista)
When using Vista, you will need to select which playback device you will want to
use. We suggest right-clicking on the speaker/sound icon next to the clock. After
right-clicking, a menu with playback devices will be listed. Left-click on playback
devices, this opens the Sound window showing your playback devices. You will want
to select the Blue Circle Audio USB as the default player.
Then check your properties on the Blue Circle Audio USB device. Highlight the Blue
Circle Audio USB, then left-click on the properties button in the lower right-hand
corner of the sound window. Next, go to the supported formats tab at the top of the
Once in the supported formats tab, put a check in all of the supported sample rates.
Go ahead and close all of the windows you opened. You should now be able to play
music from your computer directly into your USB Tunnel. Sometimes, the media player
software program needs to be restarted if changes to the settings are made while
the media player program is open.
With Vista, you may need to go in and physically change the sample output to match
what you are playing. Vista does not want to change its output from one sample rate
to another on its own. (Example: 96k to 48k) Once you set the output signal, Vista
will want to re-sample everything to the default sample rate. There are some media
players for Vista that will bypass this feature by using a plug-in called WASAPI
(Windows Audio Session API). We have found this option to help the sound greatly.
The WASAPI plug-in allows unmixed audio streams to be rendered directly to the audio
adapter and no other applications audio will play and signal processing has no effect.
USB Settings (XP)
When using XP, once the driver is finished loading, the computer should automatically
switch to using the USB output. Some media player software will make you switch on
its settings to the USB output. Sometimes, you need to restart the media player software
program if changes to the settings are made while the media player program is open.
Some media players for XP offer plug-ins that will bypass the sound kernel mixer
but they tend to be of a use at your own risk nature.
USB Settings (Mac OS X)
Once the driver is done loading, it will switch over to sending the music over the
USB connection automatically. You may have to restart you music playback software
(iTunes is an example).
With the MAC OS10, the sample rate output has to be changed manually through the
Audio Midi settings. The Audio Midi settings are under Applications & Utilities.
The icon looks like a music keyboard. After Audio Midi icon is open, the output settings
are under the Audio Devices tab. There you change the output from 44.1k to 96k and
the reverse of course. We also recommend a piece of software for the Mac to use for
playback. Amarra MINI 1.0 Computer Music Player by Sonic Studio will allow for automatic
hardware bit rate switching to the music and a purer bitstream of data.