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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 Tunnel.

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.


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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 properties window.

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.

USB Tunnel 24/96
Contact:  bcircle@bluecircle.com  /  519-469-3215