Behind the scenes (magpie)

An intresting video looking behind the scenes and the control rooms of 70's kids show magpie ..very intresting.

God I hated Magpie. Awful, awful programme.

But that was very cool to see.

I don't know if it's still there but someone uploaded a whole episode of Magpie with gallery talkback a while ago.

changed a bit now with computer graphics, no more cameras filming bits of card with words on, or rolling the credits on a big drum

I love the comedy "clunk" that we can hear on every cut whilst in the gallery! I assume it's the actual noise of the vision mixer. How annoying!

On a boring technical note do any of the boffins here know how those "special" wipes were done back in those days? I'm assuming it is too early for a DVE to be involved?

How interesting that you should use the word 'clunk' to describe the noise accompanying the switch selections - for that is what it is precisely known as in TV engineering circles. In fact, the 'clunk' was far from annoying or 'comedic'.

The cameramen used to like hearing the 'clunk' in their headphones as the vision mixer cut between cameras as it gave them a sort of re-assurance as their individual cameras were being cut up on air. Yes, of course each camera has a red light in the field of view of the cameraman, but sometimes it could/can be a bit slow or sluggish to come on to full brightness (we're talking pre-led days here!) and so the satisfying 'clunk', which obviously occurred as the pictures were actually cut, was somehow considered more definite. An important point when considering fast cutting programming as the 'clunk' follows a satisfying pace.

A very popular mixer of the era was made by CDL which used quite clunky switches, the mixer shown in this video has fader arms reminiscent of a Prowest/Richmond Hill mixers, the lever arm (used to perform the mixes) looks very much like a CDL mixer. But I cannot say for sure and it could be another make.

Back to the 'clunk'. We used CDL mixers in the studios and they gave a very satisfying 'clunk'. When in due course the mixers were replaced by Grass Valley mixers - these mixers had switches that gave very smooth and silent operation - so no 'clunk'. The cameramen missed their 'clunk'! - and so a black box was designed and installed in each studio mixer control room gallery which gave out an imitation 'clunk' whenever the vision mixer cut between two live sources. The 'clunk' came out of a small horn speaker tucked down in front of the production desk so that the control room staff could hear it and the cameramen could still hear it via their headphones.

And today? Even though the mixers have all been replaced by state of the art HD digital mixers, the 'clunk' generator is still there tucked away in front of the production desk.

Since you think that analogue mixer wipe generators are 'boring' I wont proceed any further down that path. Suffice to say rather obviously DVE equipment is certainly not required to generate wipes.

Thanks for your very interesting reply, bluecortina. I could see in that video (and another interesting one called "Thames television - Technical training video - Television production" that I found) that the vision mixer appeared to be using a fair amount of force to press the buttons! It's not surprising they made quite a noise.

Re "boring" - it is something that interests me greatly but I thought most would not find it so interesting, hence the jovial disclaimer! But if you do not wish to comment that is up to you.

Thanks again.

I can certainly recall being involved with the supply of a Sony vision mixer to Teddington in the 1990s, and the requirement for it to go 'clunk' !!

As for wipes, pre DME, it was only a case of switching back and forth between the two sources, using the horizontal syncs as a reference in the case of a horizontal wipe, the time delay for the switch would increase as you moved the fader arm from one end to the other, and for vertical wipes the same idea, but using the vertical blanking period as the reference. As for a circle etc, well, just combine the two !

Would that have been the DVS8000C?

I think your wipe example might give you a corner wipe rather than a circle!

I’ve found the video you mention, presented by Howard Steele, the ex-chief engineer of the IBA before he left to be become MD of the local Sony operation at Basingstoke when they set up their broadcast operations in the UK.

I still can’t tell the name of the mixer manufacturer in that second video, it does look like a CDL, perhaps someone here from ex-Thames will be able to tell us. I suspect the vision mixer is slightly over-egging the effort required to press the buttons perhaps to emphasise to the viewer what he is doing. The mixer panel itself also appears to have a very small display strip above the main mixer buttons themselves to ‘tell’ the vision mixer what remote sources are in use with the studio and have been mapped to which buttons on the mixer. The first 5 or 6 buttons do not have these small displays since these will be the fixed studio cameras and these are rather obviously always present in a studio (though the number may vary depending on the production) – these buttons will be permanently engraved in some way.

When the technical ‘bloke’ refers to ‘slaving a camera’ he means that camera will be recorded on a separate VTR to the one recording the main studio output. It’s a very common procedure on shows where the ‘action’ may be somewhat difficult to pre-judge. In this case you imagine it would be difficult to pre-judge when Frankie Howerd is going to ‘mug’ to camera so if you tell Frankie that a particular camera is going to be permanently on him he should have enough sense to always ‘mug’ to that camera. These days we tend to call it an ‘iso’ rather than ‘slave’ and a big LE show with a dozen or so cameras might have 5/6 cameras all being separately recorded (to be edited into the main show in post production). When a camera is being recorded on a separate vtr ( or server these days!) the on-air cue system generally puts a green cue light on the camera in the sightline of the cameraman (only) so that he knows that whilst he may not be ‘live’ at any particular time his camera’s output is being recorded for possible use at a later stage in the production process – so don’t think you can relax!

Analogue mixer wipes. I will assume you are happy with the principle that if you wanted to simply mix between two pictures all you have to do is use a varying control voltage to two amplifiers and simply add the output of the two amplifiers together. The ‘key’point is with the first amplifier (amplifier 1) if you increase the level of the control voltage the output of the amplifier 1 increases and so you ‘see’ more of the picture passing through it. With the second amplifier, as you increase the level of the same control voltage the output of amplifier 2 DECREASES and so you see less of the picture passing through it. So if you add the outputs of these two amplifies together and increase the common control voltage you will see picture 1 (from amplifier 1) begin to increase in level and picture 2 begin to decrease in level. You are performing a simple mix.

So, as you waggle the mixer lever arm all you are doing is varying the level of the control voltage to these two mixing amplifiers to perform a mix. The key point here is that it is the control voltage that is performing or controlling the mix. Suppose now instead of using your own arm on a lever arm on the mixer panel you thought “I wonder, if I could make that control voltage into some weird shapes I would probably get some weird results, and what if instead of slowly increasing the control voltage and making the two pictures mix together instead I make the control voltage switch instantly between fully ‘on’ and fully ‘off’ – then the two pictures must surely switch instantly between themselves”. You are now thinking about mixer wipes, and hopefully you have twigged that if you can control the shape of the control voltage being fed to those two mixing amplifiers then you can control the shape of the resultant mix (which happens instantly, so it isn’t really a mix – we call it a ‘wipe’). You have to let the mixer’s internal circuitry generate these ‘shapes’ – but what are they? You are now into the realms of what we call mixer ‘solid shapes’.

Imagine you are standing in your kitchen and on the floor directly beneath you is a traffic cone. Look directly down at the cone, the top of it is a point. Imagine you have a very sharp Stanley knife in your hand and you cut off the first inch of the cone. Looking at the top of the traffic cone what is the shape you see? – you see a circle. Cut off another inch and what do you see? – you see a bigger circle. Now imagine you keep slicing away at the traffic cone ‘bit by bit’, as you cut off one bit after the other the circle gets bigger and bigger until you reach the bottom of the cone. You have generated a mixer ‘solid shape’. That is all the mixer is doing, it is generating an amplifier control voltage shaped like a traffic cone shape. As the vision mixer moves the lever up and down all he is doing is the equivalent of moving the Stanley knife up and down the traffic cone shape and cutting through it – so as he moves the lever, so the size of the resultant circle varies in direct proportion to his arm movement.

Of course this is a simplification, but I hope you can see that as the lever arm moves, so the diameter of the circles change, and if you turn that into a common control voltage for the two mixing amplifiers then the combined output of the two amplifiers will be one picture inside a circle of the other. As you move the lever/arm/Stanley knife/ so the size of the circle varies.

Change the traffic cone for a small pyramid and get the Stanley knife out again – can you see that now you will generate a square wipe? Change the pyramid for a wedge of cheese lying on its side – now you will get a vertical wipe going from left to right, twist the cheese through 180 deg and now the wipe goes right to left. Move the cheese round 90deg and the wipe goes from top to bottom, and another 180deg will make it bottom to top.

Go back to the pyramid and put it on your imaginary kitchen floor. Turn it through 45 deg – what shape wipe will you get? If you’ve followed this, and I readily admit it isn’t easy for the novice, you’ll be able to tell me.

Nowadays it’s all done by the mixer’s internal computers and we don’t have to think about it at all.

Indeed it was



Yes, you're quite right, I'll get me coat !!

Your descriptions above are far better than mine.

I think Sony only sold two of those, not sure why it wasn't more popular. Maybe it was a bit before it's time (do you think?) I quite liked the MVS8000 series. I did suggest to Sony field service that maybe they could feed back to Japan that an internal 'clunk' generator option might be nice - I don't suppose it will ever happen.

Don't worry about the wipe 'stuff' ! - I used to live and breathe it, I even had a Grass Valley course .. at Grass Valley.

I used a BBC micro and eprom blower to develop and make some new matrix wipes for the GVG300 series of mixers. Keen viewers of ITV's 'Six O'Clock Show' (and GVG300 experts) might notice that show used some non-standard matrix wipes between the titles and the studio pictures on some of the later shows. You could do that then. I can't imagine it would be very difficult for today's mixer designers to include a software option to allow end users to design their own wipes perhaps using the user touch screens as the design interface - would be a novel selling point as no-one does it at the moment to the best of my knowledge.