OB

OB stands for 'Outside Broadcast'. In stoic, we have a small portable rack of equipment which can be used to create a small studio set-up anywhere, using the MX-50. However, this obviously requires a good knowlege of how such set-ups work. Examples can be found in the Previously Successful Set-ups.

What's In the OB Rack
Tech: ***

The OB rack consists essentially of a few rows of DAs (Distribution Amplifier) together with power distribution.
The 1U unit at the bottom is the MDU (Mains Distribution Unit) wich powers the rest of the equipment in the rack. It's an old-style unit with non-standard connectors but still delivers mains power through individually 3A-fused outputs. Due to the connectors however much equipment will have to be powered from standard multiplugs.
Above this is a 1U audio-video DA. This is usually used for splitting out the mix signal as it is the only point where audio and video come together. It has two audio channels on phono connectors and one video channel on standard BNCs. A point to note is that the input is 'loop-through', i.e. one connector is input and one connector is non-DAd out. The non-DAd output should be terminated with a 75-ohm terminator (as shown below)

Above this is a card-based video DA rack. This is intended for connecting sources to vision mixer monitors, the vision mixer itself and sundry general video-only DA uses. This works in exactly the same way as the two card-based DA racks in the studio. Each card is one channel, with one input and six outputs. The entire unit has a master switch on the back and is powered from a single mains IEC connector. The channel sockets go downwards in a zig-zag pattern:

Above this is a rack shelf with space for anything else that might be needed, such as a sound mixer PSU.

Fitting the Extras
Of course, a rack pretty much full of DAs is useless by itself. You will need to connect equipment up to it, i.e. the vision mixer, vision mixer's monitor rack, recording/live feeds and sometimes the sound mixer.
You may find it handy to consult Previously Successful Set-ups at the end of this section.
The general way of connection is that a DA from the cards is designated for each incoming source to the vision mixer (e.g. a camera). The outputs of these DAs are then connected one to a monitor in the vision mixer's monitor rack (often SCART-BNC connectors are required, these are usually kept in the 'Video Leads' flight case) and one to the vision mixer input. The vision mixer output is then connected to the mix DA, with outputs from the DA running to the mix monitor for the vision mixer, any live monitors which may be used (e.g. for audience use) and any tape decks that are recording.
The sound mixer usually takes its inputs directly from the sources (e.g. mikes, PA feeds, etc.). The sound op also normally uses headphones directly connected to the desk. The sound mixer output is usually also connected to the mix DA, in stereo, from where audio feeds are run out with the video feeds for e.g. audience monitors or decks.
VT decks can either be used as inputs, when the video output is connected to a card DA and the audio directly to a sound mixer line input, or outputs when all the deck inputs are connected to the mix DA.

Previously Successful Setups
Here we will consider two different set-ups; International Night and Fresher's Fair 2002.
The aims of the two set-ups are quite different. International Night is designed to get a 3-camera shoot of a live show mixed to tape, with some audience monitoring for off-stage cast and the stoic crew (at the request of the organisers). Fresher's Fair 2002 (FF from now on) was designed to get 3 cameras on an external set mixed into a main show again with audience montoring.

You can see from the diagrams that technically the two set-ups are quite similar, the only major differences being the lack of on-set sound handling on FF (the sound was run down to the Media Centre independently, as shown, and mixed in the studio) and that International Night is an entirely independent set-up.

International Night is designed to allow the live show to be mixed to tape for a small-scale edit later on and then for sale. Centrally there is a director, vision mixer and a sound mixer. The sound mixer mixes in feeds from the stage PA system (usually run from the PA desk as group outputs) with rifle mic feeds from the ceiling of the venue to get audience reaction. The director often just moves the cameras around and relies on the vision mixer to make good cuts owing to the speed of many of the acts. As can be seen everything is simply run to tape, with a couple of monitors with mono sound run on their internal speakers for general audience consumption. Usually these are sited on levels 3 and 4 of the Sherfield Building, with an extra (video-only) feed being run last year to a lecture theatre on level 5. The theatre was equipped with a video projection system and there were already tie line installed to backstage of the Great Hall. All we needed to do was to run a mix line along the voids to a stagebox situated on the production right front of the stage. This connected to a tie in the lecture theatre projection room, which was then linked into the theatre's projection video switch.

The idea when FF was designed was to minimise the amount of equipment that needed to be installed on-set as all this was temporary and hence much more likely to fail than the installed equipment in the Media Centre. The reason for the lack of on-set sound handling was due to the lack of crew and a suitable mixing desk rather than any major technical consideration.
So a minimalist set-up was used in the quad, with only the cameras mixed and mics and monitors wired, and this was tied into the existing set-up via external ties in the TX suite. These external ties run back to the cool room, where they were patched to the relavent places in the set-up. Unfortunately we have no 'spare' matrix channels as such so it is necessary to repatch the less-used ones for a set-up like this. We patched studio monitor line 2 (used for the light ents set monitor) onto the on-set monitor in the quad and patched the director's matrix monitor over the cool room monitor. We took advantage of the fact that the matrix panels communicate using a loop of 75-ohm video cable so we could directly patch the quad matrix control line through the video cables over the cool room matrix control loop (for more on matrix control see What Is The Matrix? - Button Panels).
Audience monitoring was run directly from the TX suite, not via the cool room. As the broadcast signal enters the TX suite and runs through a DA prior to modulation (see Broadcast) we simply connected the relavent loom cores into the DA to run the monitor and speakers.
During the broadcast, VTs were run in via the JVC vision mixer downstairs in the Media Centre along with live news bulletins from the studio. The signal from the quad vision mixer was run into the matrix where it was routed via a TBC into the JVC vision mixer, allowing cuts in and out to be made easily and also allowing captioning from the Abekas CG. The microphones were run back over external ties and patched into the cool room onto mic channels on the K1 sound desk allowing the downstairs sound op total control of levels. This required two directors, one taking care of the camera direction in the quad on the MX-50 along with a floor manager and one in the Media Centre taking care of cuts, VTs, items etc. A single talkback loop was run for everyone; as there are a couple of patchable talkback spurs in the cool room. One of these was patched to an external audio tie where it was patched into the quad loom. The quad director, floor manager and camera ops all had units run on this loop allowing easy communication with the studio.