What Is The Matrix?

STOIC's studio system is based around a 32x32 matrix manufactured by Grass Valley. In essence, this is a giant switch in which any of 32 inputs can be connected to any combination of 32 outputs. However, it is more complex. It simultaneously switches a video channel and up to three audio channels. The upshot of which is that you can plug VT outputs of video and stereo audio into one input and have them all routed to any or all of the outputs.
It consists of two crates in the cool room. One switches the video and one audio channel, the other two audio channels. They are controlled together through interlevel control, explained later. It is wired such that stereo audio is controlled through the audio-only crate, with a plan to use the third audio channel to run tally.

Sources
Any input to the matrix is referred to as a source. The simplest source is a camera, which simply inputs a picture on its channel. VTs are more complex as they simultaneously input video and two audio channels. The matrix system usually switches all of the channels simultaneously although it is possible to override this and route audio and video seperately using the X-Y panel

Destinations
Any output from the matrix is referred to as a destination. All studio equipment requiring inputs is run directly from a matrix destination via patch (such as studio and control room monitors, the vision mixer, edit suites, VT decks etc.).
Any output can be associated with a button panel (fully described later). These can be seen throughout the control room, voice-over booth and cool room. By pressing a single button on one of these, the signal through the output is connected to the relavent input.

Interlevel Control
Tech: ***

Inside, the system is designed to be extensible to up to 128 inputs and outputs of an arbitary number of channels. Hence, the crates form a chassis and as such there are no immediately designated 'master' or 'addon' units. This can be seen from the fact that both of the crates in the cool room have all of the control sockets on the back.
Obviously, both cannot control the system however. The complete system control is via three boards in the top of the crates; one is a control board, one an identical backup and the other a switching system to transparently switch to the backup board if the master fails. Our system does not, at time of writing, have a backup board. If you examine the crates, you will find that only the video crate has a system board in it. The other crate is controlled by this system board via a large multicore running between two d-sub sockets on the back, known as an interlevel connector.
This is because each seperate channel of the matrix is known as a control level. Our system has four, designated V, A1, A2 and A3 (Video, Audio 1, etc.) It is possible to configure the button panels to control any combination of these levels by switching one of the DIP switches inside the panel. Normally all levels are switched. Here the levels are designated by numbers. This system works as follows:
Imagine the two crates stacked on top of each other.


The X-Y panel can also switch different parts independently using buttons on its main panel.

X-Y Panel
Tech: **

As its name suggests, the XY panel allows the user to directly connect any of the inputs(X) to outputs (Y). It is mounted in the control room above the vision mixer console.

The destinations are specified as the number of the socket on the back of the crate; a list of matrix destination numbers is on display next to the panel. The sources are known by alphanumeric identifiers known as 'Transcodes' which are set up using the matrix RS-232 terminal interface onto the raw socket numbers. These transcodes are also shown on the status display. The idea of using them is to make routing more intuitive.

Each transcode is made up of a type and a number, for example VTR1 is tape deck 1, TBC4 is TBC 4 (surprisingly). Here is a full list of types:

BLK - Black
CAM - Camera
VTR - Video Tape Recorder
CG - Charactor Generator
MON - Sustain
ED - Edit Suite
TL - Tieline. This can be a studio or external line.
TBC - Timebase corrector
TK - This stands for TeleCine, a device for transferring stuff shot on cine film to video. We don't use film so we don't have one; instead this designation is used for sources that do not fit anywhere else.
   TK1 - Mix
   TK2 - Preview
   TK3 - DSK Preview
CLK - VT clock; this is not used in STOIC as VT clocks are put onto material on the edit suites
CAS - not used in STOIC
TC - not used in STOIC
TST - not used in STOIC
SP - not used in STOIC
BARS- Colour bars not used in STOIC as we do not have a dedicated colour bar generator. If colour bars are required, the MX-50 vision mixer can be connected into the system in the control room and patched into the matrix. This can provide colour bars.
AUX - not used in STOIC

Most of our equipment is labelled with its matrix designation. An oddity is the Abekas A72 charator generator which has a regular output and a 'preview' output which shows menus and is used to edit pages. The regular 'programme' output is called CG01 and the preview output is called CG02. For this reason CG02 should not be put into the vision mixer as it's not intended for the audience to see. The hard disk stores are labelled as VT decks.

Button Panels

Most of the channels are controlled through button panels. These are single strips of 32 buttons, found throughout the control room, which are associated with a single output. Each button represents an input.
Each panel is assigned an output which it controls and a 'station address' which identifies it to the central crate, via DIP switches set into the top of its case. Although two panels can be assigned to control the same output, no two panels can share a station address (think of it like a computer network address).
Although the panels look simple, they are surprisingly complicated. The 32 buttons on the front do NOT necessarily correspond to the 32 matrix inputs. Each button on each panel can be individually configured to relate to any input using the terminal interface.
Each panel also has a 'protect' button. When this function is enabled, no other control panel (including the X-Y) can alter the setting of that output (it generates a 'protect error'). However the panel on which the protect is set can still alter the output as per normal.

The panels are powered independently using a 9-pin D-sub connector on the back. We have suitable power supplies for all of our panels. The BNC connector connects the panel to the central crate via a 'control bus'. This is essentially identical to a BNC thin ethernet loop, common in old computer networks. HOWEVER, it DOES NOT use the same cable. The matrix control bus runs along video coax, with a nominal impedance of 75 ohms. Ethernet uses coax with an impedance of 50 ohms. So you cannot use ethernet cable to run control buses; you must use video coax. Since we are in a TV studio, this is (un)surprisingly handy. It also means that the control buses can run through video patch, as they do at many points. A note is that the XY panel runs through the same control bus and the status display is also connected to it.
The matrix has four seperate control buses. Each is identical and any panel can be plugged onto any of the buses. They all emerge straight onto patch in the cool room and so can be repatched to anywhere, including video tie lines. They are normalised to:
- Control room vision
- Control room sound/voice over booth
- Control room edit
- Cool room
Any of these can be repatched but the author recommends repatching the cool room for external use (and maybe the edit desk if needed) since in a large live set-up the others are likely to be in use.

Status Display

The matrix status display is housed in a 1U unit below the monitor in the cool room. Like the rest of the matrix it has space for a redundant power supply which is not fitted, so only one of the power lights will be on.
It is connected to a matrix control bus and outputs a picture similar to the above as a standard composite video signal. This output emerges in the main vision patch in the cool room but is not normalised to anything. So if you need to use it, you must patch it to a monitor or matrix input. Personally I prefer using the latter because then I can access the display anywhere in the studio.
Normally it displays a table with the first column giving the output numbers of the matrix, the second giving the transcode of the video source connected to the output, the third giving the transcode of the first audio source connected to it and so on (remember that the matrix has three audio channels). You can spot failed crosspoints easily because the status display gives '-----' if it cannot detect a functioning crosspoint. Protected channels are shown up as inverse colour.
The status display also has its own control panel mounted directly above it in the cool room. This allows the user to select what is displayed. For example only certain channels can be displayed, transcodes or socket numbers can be displayed etc.
**************TODO: exactly how to use display panel*************
Finally the status display also has a lower-level configuration set using DIP switches. These are mounted within the unit so you must take the front off it first. In order to do this, pull the plastic handles on either side inwareds towards the centre of the unit. The front will then come away. There are three DIP switches mounted on the centre board:

Terminal Set-up
Tech: ***

Basic set-up for the matrix is carried out by connecting a terminal or a computer serial port to the RS-232 terminal socket on the back of the controlling crate. This connection is a female 25-pin D-Sub. We have a suitable hyperterminal configuration file for use straight away but in case this file has been lost, you're using a different machine, etc., here are the sattings:
**********TODO: what are the damn settings??***********
When you first connect, nothing happens. Type CTRL-P to bring up a prompt. Then type H ENTER to bring up the help screen which lists all of the commands.

Transcode set-up
The most likely reason you would be using this is that you're configuring some button panels or adjusting the transcode settings.
As stated before, matrix transcodes are made up of a type code of up to three letters and then some numbers. The type code table can be adjusted using the ????? command. The matrix responds by prompting you to enter, in turn, each new type code. Just pressing ENTER will leave the current setting unchanged.
The master transcode table can then be changed. This is the table with which the matrix relates transcodes to socket numbers. Entering the ???? command causes the matrix to prompt for a transcode to each socket in turn. You can enter a number after the command, e.g. ???? 7, to start data entry at that socket number.

Again, just pressing ENTER leaves the current setting unchanged.
If you alter the transcode table, however, you may find that the button panels stop responding correctly and throw up errors when you press certain buttons. This is because each panel holds its own table relating its buttons to a transcode. The terminal interface allows you to alter these. At the time of writing, all of our panels are set up identically to relate to the direct socket numbers.

IMPORTANT Remember that we are currently dealing with station IDs not output numbers. Most panels have different station IDs and output numbers. Attempting to write data to an output number will most likely write it to a completely different panel and runs the risk of having to reconfigure every panel in the system back to how it should be. BE CAREFUL!

The easiest way of setting up a new panel is to copy the settings from another panel. Use the ???? n command to load in the table from the panel with station ID n. The ???? command allows you to check that it has loaded correctly. You can then modify this in the same way as the master transcode table using the ???? command. Again, this prompts for a transcode to be associated with each button in turn. You then use the ???? n command to write the table in memory to panel with station ID n. You can read it back with the ???? n command and display it with the ???? command to check that it has been written properly.
*******TODO: other uses of the terminal interface************