Tech: **
Note: it may be handy to consult Appendix 1: Wiring Diagrams when reading this as it shows diagramatically how all of the pieces fit together.
In many ways, the vision mixer can be considered as the center of the vision system. All signals to be broadcast or recorded pass through it and the operator ultimately decides what is recorded or transmitted. (From now on, the terms 'transmission' and 'broadcast' will refer to anything being transmitted live or recorded to tape. From most perspectives the processes are exactly the same)
The studio system is based around a JVC KM-2000 vision mixer. This has 8 basic channels, i.e. buttons behind which there are normal pictures (keying and special effects are considered later), which are connected to the first 8 matrix outputs. Hence they can be directly connected to any signal within the studio system (NOTE: any input to the vision mixer must be genlocked). The mixer also has three 'buses', i.e. rows of the eight channels. Each bus can have a different source selected on it and the mixer output (known as 'programme output' or simply 'mix') is a composite of one or more of these.
Internal logical diagram of KM-2000. Effects and keying are left off for simplicity.
It can be seen that the relative amounts of the source selected on each bus are controlled by the two faders on the desk. The upper fader, in both the diagram and physically on the control panel, sits between buses A and B and is designated 'SE' (Special Effect). This does not just mix the two buses together but can also wipe between them and place the image from one bus inside the image from the other. This is controlled using the mix selection buttons at the top of the console. The fader can also split into two seperate faders by releasing a button in the top to control the width and height of box wipes seperately. You can also switch on the positioning joystick in the upper right corner of the panel (the switch is directly below it) to move box and circle wipes around the screen.
The mixer offers three kinds of keying: chrominance (i.e. bluescreen), lumniance ('super-impose') and downstream.
*********TODO: preview bus*********
Finally there is the 'Mix Switch' which is the three buttons located under the positioning joystick. During normal operation this is set to 'EFF' (EFFect) which is the normal mixer output. It can also be set to AUX, the auxiliary input, which is connected to a matrix output. It is normally routed to sustain (see standard set-ups later) and for this reason is currently referred to as the 'panic button'. The other option fades the mixer output to black; this is known as the 'uber-panic button'.
The signals going into each of the main channels are shown on the eight small monitors directly above the vision console. The left-hand of the two larger monitors shows the preview output of the mixer and the right-hand the mix output.
The system is designed so that in the event of a major failure in the KM-2000, the Sony MX-50 desk used for OB can be 'dropped in' to the set-up with a minimum of effort. Directly below one set of MDUs (Mains Distributuion Unit, a 1U rackmount box with lots of lights and fuses on) in the bottom of the vision furniture is a strip of BNC plugs. The first four are mixer sources for the MX-50 and are connected to the back four KM-2000 mixer sources, i.e. the lower row of monitors. They can be plugged directly into the back of the MX-50. The fifth is plugged directly into the MX-50 programme output. The line emerges in the main cool room vision patch where it is not normalised to anything. In order to switch to using the MX-50 simply remove the U-link normalising the JVC output into the station mix out and patch the MX-50 output to it instead (for more information on video patch see Patch and How It Works in the Concepts section. Don't even think of messing around on the cool room patch unless you know what you're doing.)
Studio Stage Boxes
How the Cameras Fit
From here, the camera picture is normalised onto the matrix via the cool room vision patch. The return video signal is identical for each camera; as can be seen from the diagrams, it is run directly from a DA into each CCU. The DA input comes from the main vision patch, where it is normalised to ???preview??? from the vision mixer. Genlock comes directly from the sync pulse DAs.
The black Sony EVW-300P camera does not have a multicore connector and cannot be connected to a CCU. When used in the studio, seperate genlock and video lines must be run to it from one of the stage boxes in the studio. Stage box connections are detailed above. In regular set-ups stage box sockets may be patched onto camera lines in the cool room. Look for signs on the sockets telling you where they are connected to.
How the VTs Fit
Extra Sources
Standard Set-up
Tie Lines and Things
For examples of the more ambitious things we've done with the system, consult previously successful OB set-ups in the OB (Outside Broadcast) section.
From Vision Mixer to the World
Importance of Phase Adjustment
The other adjustment is horizontal (H) phase, which simply controls how far shifted across the screen the image is. The control for this is in the same place as the SC control.
Since analogue equipment can 'drift' it's recommended that the tech manager should check that everything is still in phase properly once a term. Only sources which are genlocked need (or indeed can be) adjusted in this way, including the TBCs.
The output from this fader is fed directly into bus C where it sits behind the button marked 'SE' and into one of the inputs of the lower fader, with the output of bus C being the other. The lower fader can only fade between bus C and the output of the upper fader.
Chromakey (sometimes referred to as CSO, Colour Seperation Overlay but commonly known as 'bluescreen') is where a picture is brought into the mixer with a designated background colour (usually either blue, green or yellow. We have a large blue screen in the studio). The mixer is then told what this background colour is, either by selecting on the dials in the chromakey control area (towards the top left of the console) or by an external video signal giving the colour. Which is used is selected by a switch on the console. The mixer then superimposes the given picture over the picture from another bus, with the selected background colour being transparent.
*********TODO: find out which channels are what in keying. Seperate to a vis mix ops manual??******
There are two sets of BNC video connectors in the studio, on wall-mounted stage boxes. Connectors 1-8 are located on the pillar with the 'on-air' light, below the camera multicores, and connectors 9-16 are located on the 'far wall', near the door to the aircon plant.
All of these connectors run through to the cool room video patch, where they are normalised as follows:
-The first connector on each box (i.e. numbers 1 and 9) are connected to monitor lines 1 and 2 respectively. These are fed from matrix outputs ???? via the patch. If any on-set or off-set monitoring is required then it is recommended to use these lines as they can be matrix-routed using the X-Y panel without needing any patching.
-The next three connectors on each box are designated as studio returns, i.e. the signals flow from the cool room to the studio. Connectors 2,3 and 4 are normalised to genlock while 10, 11 and 12 are not normalised to anything.
-The final four connectors are designated as studio sends, i.e. the signals flow from the studio to the cool room. The first two of each (connectors 5, 6, 13 and 14) emerge in the cool room vision patch and are not normalised to anything. The final two on each box (connectors 7, 8, 15 and 16) are normalised to matrix sources and designated ST7, ST8, ST15 and ST16.
It is usually not necessary to use these as the white DXC-3000 cameras can use the multicore looms provided. However if you are using more cameras or have extra equipment in the studio you may need these lines.
Note - this describes how the sockets are normalised, not necessarily how they are currently connected. Look for labels on the sockets and 'current patch' lists to be sure of what is connected where
IMPORTANT - you MUST get authorisation from the tech manager before altering any patch connections in stoic. Phone them if necessary. Also do not be tempted to even touch the patch unless you are familiar with how it works. See Patch & How It Works in the concepts section if you are unsure.
As can be seen in the wiring diagrams, the studio cameras are connected into the system via 14-pin multicore cables which enter the studio near the pillar with the 'on air' light mounted on it. These cables carry back the camera picture into the system and carry tally, genlock and 'return video' (described later) into the camera. They run from the studio back into the cool room where they connect to CCUs (Camera Control Units). In essence, these are remote controls for the cameras. They allow the operator to manipulate all of the camera video settings including phase adjustment from within the cool room. They also act as an interface, taking in genlock, return video and tally signals and putting out the camera picture.
Front panel of one of our CCUs
As can be seen in the wiring diagrams, all of the VT decks are installed in the control room. Three video lines run to each from the cool room; a genlock line directly from the sync pulse DAs, an input line running from the matrix and an output line running to the matrix.
A note on genlock - Most of the decks cannot genlock themselves so the genlock line is redundant. The decks that use it are the SVHS and UMAT decks. As noted in the vision mixers section, any vision mixer input must be genlocked. For this reason there are four TBCs situated in the cool room (Time Base Corrector; for more information see Concepts: Analogue Video). These can genlock any signal coming into them. As can be seen in the diagram, each of these is run from a matrix output and acts as a matrix input. So to connect say the Hi8 deck into the vision mixer, you cannot simply connect the deck to the vision mixer input using the matrix XY panel as the signal would not be genlocked. Instead you use the XY to connect the input of one of the TBCs onto the output of the Hi8 deck and then use it again to connect the output of the TBC to the required vision mixer channel. This is made much simpler in the standard set-up described later.
Since the UMAT and SVHS decks can accept a genlock signal this is not necessary for them but may be preferable for simplicity of set-up; again, see the standard set-up described later for an example.
The Dupe Rack (short for Duplication Rack) is situated under the edit suite desk in the control room. It consists of a few old VHS decks, each of which has its input connected to a DA which is fed from the matrix and its output connected into a switch which is connected to the edit suite monitor. It does NOT output into the matrix. It can be used to easily run off multiple VHS copies of projects but as there are only a few decks and the quality isn't that high the author would recommend outsourcing any major duplication required, such as International Night or promo videos, as it tends to be quicker and give a higher quality tape at the end of the day.
Dupe rack logical wiring diagram. Note that audio follows exactly the same path in stereo pairs, except that instead of running to the video monitor it runs into the edit suite audio amp. It is possible to select whether to monitor the edit suite or dupe rack via controls on the video monitor and audio amp panels.
The Abekas Charactor Generator consists of a crate situated in the cool room connected via a control line to a control panel in the control room (for information on 'Tub and Crate' arrangements see Concepts: Equipment Control).
As mentioned previously, it has two outputs; 'programme' and 'preview' designated as CG01 and CG02 respectively in the matrix. 'Programme' or PRG is the output which the viewer is meant to see; it simply contains the text or running animation. The author tends to have it routed into the vision mixer downstream-key (DSK) input which allows for easy superimposition onto the live output. 'Preview' or PRV is the screen used to compose the text. It has a menu system displayed at the bottom of the screen and displays 'safe title' borders and cursors. It can also preview animations.
As operation can be fairly complex you should consult the Stoic Abekas User Manual for full details on operation.
Both outputs are genlocked and so can be fed directly into the vision mixer, although generally it is not desirable to have the preview output routed to the vision mixer as it is not intended for the viewer to see.
It is important to note that although the Abekas keyboard is connected into the crate via an RS-422 line running back to the cool room it does NOT use the RS-422 communication protocol. The control line was mis-specified when constructing the media centre and so it was necessary to place a custom-built cable standard converter (aka 'Bodge') into the cable at the control room end to make the signals suitable to travel down the cable. For this reason also the keyboard is powered independantly in the control room via a PC power supply mounted in the furniture.
The Accom Hard Disk Store also resides in the cool room and is controlled by a panel in the control room. The Accom panel does use RS-422 to communicate with the crate and has its own power supply via an IEC socket on the back.
The system actually contains two independent channels. It is possible to map any of the disks in the system onto either channel but not both simultaneously. The playback controls on the panel (jog wheel, buttons, playback type etc) can affect either channel or both at the same time via two toggle switches marked 'Channel A' and 'Channel B' which light up when they are selected. If one channel is playing and the other is selected then it will continue playing indefinitely until it is selected again and another command sent.
It should be noted that the Accom actually runs on a digital studio wiring system called SDI (Serial Digital Interface). This also uses BNC plugs and 75-ohm cable but is digital and completely incompatible with the analogue system which we use. At the time of writing the Accom is connected using its monitor outputs, which are analogue video but only black-and-white. It is also possible to bring up a banner showing the current video position, channel and such; as this looks ugly it is not recommended to do this while it is possible that the output can be seen by the viewer. It is possible to connect in the 'real' output using an SDI to analogue converter but these are rather expensive. However there is currently a plan to do this 'at some point'.
Channel A appears on the matrix as VT-9 and channel B as VT-10. Neither of these is genlocked as the outputs are only meant for monitoring. So in order to run it thorough the vision mixer it must be sent through a TBC like most of the VT decks.
All this is fairly complex and you may by now be thinking 'how on earth can I run my studio session? I don't understand half of this!'. Fortunately you don't need to. When the studio was designed, we took into account most of the studio session scenarios we could think of and tried to make them as easy as possible to achieve while leaving enough functionality that the studio could be used for pretty much anything by someone with enough know-how. For this reason you probably won't need to worry about the intricacies of patching, matrix interaction, genlock, etc., you can simply plug and go.
The standard set-up is as follows:
The upper four monitors in the vision desk show mixer sources 1-4, the lower four monitors show mixer sources 5-8. Normally the first four sources are matrix routed to camera lines 1-4 and do not need changing. Normally the back four sources are matrix routed to the TBCs, with TBC 1 going to mixer source 5 and TBC 4 going to mixer source 8 (this makes sense when you think about it). Again these do not normally need changing. Sources 7 and 8 are designated as 'Switched VT' which means that for most sessions you just run all of your VT through them. The two matrix panels directly below the mix monitor control the input. However, they do NOT control the inputs to mixer sources 7 and 8 directly. The panels control the inputs to TBCs 3 and 4 which are kept routed to mixer sources 7 and 8. So you do not have to worry about genlock when using these lines; simply select the VT deck which you want to see and it will appear in the vision mixer nicely genlocked and corrected.
The larger monitor to the left shows the vision mixer preview output and the one to the right shows the vision mixer programme output, i.e. what runs to tape or broadcast. The two smaller monitors next to it, in the third bay from the wall, are simply cueing monitors for the VT operator and are not directly connected to the vision mixer system. They are controlled by the matrix panels below them. The four matrix panels at the top of this bay control the inputs to the VT decks most likely to be used for recording. Normally these will be left at 'mix' or 'black' unless you are doing something like recording cameras separately or something coming in on a tieline while showing something else
A note on feedback - If you route mix into a VT deck while it is stopped and its output is selected to mix on the vision and sound mixers you get feedback. This is bad for the equipment and anyone's ears who happens to be wearing headphones. So the VT destination panels are usually kept at 'black' unless you are actually recording. Always check that your recording deck will record what you want it to by selecting it onto one of the VT cueing monitors to avoid embarrasing conversations with producers who just realise they will have to repeat a major studio session.
The standard set-up was concieved for a medium-sized studio shoot. So, if you are using four sets simultaneously or tie-lines connected to cameras outside the studio you will probably find it sufficient. Otherwise you are likely to have to start messing around in the patch.
If you are using live cameras outside the studio then they must be patched into the matrix. All of the Media Centre tie-lines run into the transmission suite at the end of the corridor. Only chairs and technical managers have access to it. From here, there are ???eight???? video ties and audio stereo pairs running into our cool room designated as 'external ties'. Of these, the first three are normalised into the matrix (including the audio) while the rest terminate in the patch there. So in order to run an outside camera or whatever, first it must be connected to a tieline running to the media centre. This tieline must then be patched into Stoic in the transmission suite and possibly also patched within the Stoic cool room if it is not matrix normalised.
Things To Remember:
-Make sure you understand how the patch works before you go anywhere near it. The best way is to get the technical manager or, if you are the technical manager, your predecessor to demonstrate how it works. You will need the Tech Manager's permission to start doing this kind of thing anyway
-Make sure that you know what will and won't be genlocked. Remember that any source which is not genlocked must be run through a TBC before appearing in the vision mixer. Genlock is sensitive to the length of the cables used, so it may be necessary to adjust the phase of the signals coming in using the TBCs. For this reason it's usually easier not to bother genlocking an external source into the studio, rather run it through a TBC.
-When you've finished put things back as you found them!! There's very little more annoying than coming in to do a studio session to find that all of the designations have changed and haven't been labelled. It can waste hours as the tech crew attempt to correct it, and remember that the next crew to use it don't necessarily know as much as you do about the set-up.
So, what happens to the vision mixer output signal? With reference to Appendix 1, you can see that the mix signal is fed via patch into a DA. This allows other equipment to be patched in to produce the mix signal, notably the MX-50 vision mixer. This DA splits the signal out many ways, one going back into the matrix to make it switchable, another going directly to the control room mix monitor and a few extra ones appearing in the vision destination patch to allow it to be sent down tie-lines. The last output feeds into the airswitch in the sources rack. This is a computer-controlled switch whose output is connected to the modulator in the transmission suite, again via patch. Behind this switch everything is 'live'. The modulator is connected to a UHF DA which is then directly connected to cables running to the JCR, Union bars, etc. This part of the system is dealt with in Broadcast.
Tech: ***
Theoretically, you shouldn't have to worry about this because the tech manager will keep everything correctly set up and in trim for you. But just in case...
Technically, I am referring to adjusting the subcarrier phase of the signal relative to the input genlock signal. Practically, you sometimes need to adjust kit for the colours to come out right.
The easiest way to check if you need to adjust the phase is if a picture seems OK on its source monitor but appears washed-out, excessively dark or the wrong colour on the mix output. Since outputting a programme with cameras and tapes appearing different colours looks very unprofessional this needs to be corrected.
If you look at the incorrect mix picture on the cool room scopes, you will see that the vectorscope signal does not line up with the little blocks on the screen (the scopes are described in Genlock in the concepts section). Also if you ouput colour bars from the camera or feed colour bars through the TBC or whatever, they will not appear correctly.
The left-hand picture shows an out-of-phase signal on the vectoscope and the right-hand picture shows an in-phase signal.
So, what do you adjust?
Firstly, the cameras. On the DXC-3000s (the white cameras) there is a small panel on the left-hand side of the camera which you can flip open. Under it are two preset potentiometers ('pots' for short) and two switches. We are concerned with subcarrier phase, marked 'SC'. If the colours appear really wrong (like blue appearing as orange or something drastic like that) try flicking the SC switch. This brings the burst phase through 180 degrees and should make the picture look better. For more fine adjustments, you will need to find a small crosshead screwdriver and adjust the 'SC' pot. While doing this it's easiest to route mix onto a studio monitor so that you can see what you're adjusting as you're doing it.
The EVW-300 camera (the big black one with the defunct Hi8 deck in it) has similar adjustments under the panel below the VU meters on the side. The relavent controls are closest to the lens.
(An amusing note is that we borrowed an additional DXC-3000 camera for Fresher's Fair 2002 to cover the studio newsdesk while the other three cameras were on an upstairs set. However, we forgot to check the phase setting and as previously mentioned you can't see any difference on the source monitors. Suffice to say that when we cut, live, to the studio for a news bulletin James appeared a nice shade of orange, with pale blue skin and the set looked interesting as well. This was due to the 180 degree SC phase switch being in the wrong position. So be warned! Always check phase adjustment before live broadcast. This is as simple as checking that every source looks OK on mix before you go live.)
The TBCs can be adjusted using their front panels in the cool room. You just press SHIFT twice then the SC button (the buttons have multiple functions). You then use the up and down controls to alter the value, spinning the vectorscope trace.
The A72 charactor generator has its own genlock and may also need to be adjusted. This can be done from the control room using the preview screen. On the keyboard press the 'System Setup' menu button, then press the function key for 'System Timings'. You then have to enter a password (at the time of writing this was the software version, V5.00). There are then coarse and fine SC adjustment options in the menu which are adjusted like anything else on the Abekas. For more information see the STOIC Abekas A72 user manual.
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