The DI BOX

A DI (pronounced dee EYE) unit, DI box, Direct Box, Direct Input, Direct Injection or simply DI is an electronic device that connects a high impedance, line level, unbalanced output signal to a low impedance mic level balanced input on our mixers usually via XLR connector. DIs are frequently used to connect an electric instrument or a presenters computer audio to our mixing console's microphone input. The DI performs level matching (mic or line) and balancing to minimize noise, distortion, and ground loops. (previous text was lifted from wikipedia and slightly modified)

Here in AV we use 2 different DI boxes; One is the PROAV1 Multi-media DI made by Radial. The other is the dPDB (dual passive direct box) by ART. Both boxes have Ground lift and Attenuation. The ground lift helps rid your sound system of that annoying buzz that results from ground loops in the audio system. The Attenuation switch is there to help deal with a output from a device which may be to "hot"

The PROAV1 has a 1/4" in/thru, Stereo RCA in/thru, 3.5mm input and a +4dB Line XLR input. The +4dB Line XLR input can be turned on by depressing the XLR input select switch on the side of the box- A arrow points the way. The most common use for this box in AV is this: A presenters laptop is located more than 6' from your audio mixing board. laptop audio (unbalanced stereo output) goes into direct box, direct box uses balanced xlr output to run to mic input on mixing console.

The ART dPDB has two 1/4" in/thru's which can convert unbalanced mono signals to balanced mono which can be output on XLR cables.

Jeff's set up suggestion: Make sure that the laptops audio is set to roughly 50% so that the signal is not over or under driven when it gets to the board. To test your laptop audio level, play intended audio from laptop, set the gain on the mic (laptop) input channel so that it is hitting just under zero on the VU meter.

Next month...Press Boxes

Digital Recorders in A/V

Faculty, Staff or Grad students wishing to check out a digital audio recorder are in luck. A/V offers 2 great recorders for check out; The Edirol R-09 and the Olypmus DS-40.
The Edirol requires 2 AA batteries and a SD(HC) card (up to 16GB). It can record 2 Hrs/24 bit WAV or 13 Hrs/320kbps MP3. The onboard microphones makes this a great recorder for recording musical instruments for your class.
The Olympus DS-40 takes 2 AAA batteries and uses its own internal memory to record. It Records in Windows Media Audio(WMA) format and depending on the quality you specify, you can get 8 to 136 hours of recording time off the 512MB internal drive. Mics are good quality and make great recordings of interviews.

Projectors and the Black Box

The "Black Box"; What is it and what does it do. the Black box is a Video extender/distributer. We use the black box in situations where we need to run a SVGA signal from a computer to a projector that is a great distance away, anything over 100' (30.48 meters). The black box allows us to send not only the vga signal, but the audio signal also, up to a projector and sound system 500' (152 meters) away.

1. The "local" black box is connected to your computer; The "remote" black box goes with the projector. The boxes send a signal over cat 5 cable.

2. The input on the local box is for your computer and requires a M/F VGA Cable. If possible, always keep this cable attached to the local black box

3. Always use straight through network cables. Crossover cables will invert colors on the projector.

4. Remote unit has Equalizer selector switch to adjust signal gain.

You must keep these items paired properly in order to work them.

Here are all the pieces needed to make the black box kit work:

-Local unit

-Remote unit

-6' VGA M/F cable

-6' VGA M/M audio cable

-(2) Power supplies

-(2) Power cords

Sennheiser Wireless Camera Kit

OK, So if you want to use a wireless microphone for a video camera, the wireless sennheiser camera kit is the way to go. It is composed of a 2 possible Transmitters (although only 1 can be used at a time), Receiver which can mount to the top of a video camera, ME-4 cardioid mic, 3.5mm locking plug to XLR and a 3.5mm locking to 3.5mm non locking plug.
So although this is not technically a drawing, it's my blog and I want to include it.
-Jeff