Wednesday, October 9, 2013

The Inlay Desk

This week on the BBC series: the inlay desk, a special system for generating keys and other special effects for use during programs.

The inlay desk was basically a camera aiming down at a backlit desk. But it does appear to have more controls than just being a camera. Unless of course, those controls to the left side of the operator are just a form of CCU. Apparently, as the studios were colorized they were upgraded accordingly to have multiple layers of video color separation. Can't image how that would look or work, but sounds pretty awesome. In this particular picture it's neat to note that the camera looks almost exactly like the camera in the NODDY array. This is probably not too much of a surprise because the NODDY array was basically a generator of keyed graphics (at least when color came around).

Not too much out there on this piece of equipment. Most of the info I have comes from TV Studio Histories again. I can't find too many mentions of it in engineering documents, but it also took me a while to learn that EP5/512 meant "that video mixer with the faders."

If one were to piece some things together from the aforementioned website, there is discussion about the formulation of a video effects studio. Until it was built, video effects were done in the galleries of TV studios that were undergoing a set change and therefore idle. This was most likely one of the pieces of equipment they used to generate the various effects, as every studio gallery had one. There is however, no mention of the device being installed in the new video effects studio, but by that time, the 80s, I would assume it was probably thought obsolete.

This device does kind of remind me of another device developed in America, although with greater and different capabilities, called scanimate. Scanimate had an input device that was similar to this setup, but could do more, in the sense that it could alter the scan rate of its camera. This ability had the effect of making things "roll" as the image produced by the camera was re-photographed with a standard camera. Essentially it took advantage of the effect that occurs when you try to film a CRT screen. There was way more to it, but we were trying to stick to the BBC weren't we?

On a personal project note, I have been playing around with transistors (still) and am working on several guitar pedal-like devices as well as germanium input amplifiers for microphones. In addition, also bringing an ADAT digital tape recorder back to life. Perhaps another week.

To leave you today, I found a cool video montage about Television Centre that has become one of my favorites. Enjoy

Wednesday, October 2, 2013

The BBC EP5/512 Vision Mixer

This week we take a look at one of the most unique video switchers that I have ever seen, the BBC EP5/512 vision mixer:

bbc ep5-512 vision mixer

However, to call it a video switcher is misleading. It does more than your average video switcher, and that is why it is referred to as a "mixer." Just looking at it can tell you why that is. This "mixer" has the unique quality of being able to switch or mix up to 8 sources at one time. Rather, it has two modes- switching and mixing. Like any 8-source switcher, there are two banks of inputs, with switches to select what is present on that bus. The two banks can then be switched or wiped based on a special effects panel. Pretty standard for a switcher. The only neat thing in this section is that there are pluggable units for the effects section that expand the available wipe effects up to 106. Still, pretty standard.

bbc ep5-512 vision mixer effects1
The effects panel of the ep5/512, showing pluggable wipe units in upper right corner

The special features of this mixer appear when you start asking what the faders are above the selection switches. These actually form an additive mixing section for each bank. When the mixer is in switching mode the faders are inactive. However, when a fader is topped (brought to its highest position), the selection switch pops out and the bank is now controlled by the mixer section. Theoretically all eight channels could be combined in the image on the screen. The mixer has limiting circuitry built in to prevent the image from deviating from standard transmission line voltages. With this ability, very complex layered images can be created. Certainly with modern cascaded switchers, complex overlays can be done, but it would require multiple buses and effects bars sitting in their (I feel, unstable) middle position. Also, with a setup that takes up the same room as a single bus 16 input switcher.

To switch back to switching mode, press a selection switch and control is returned to those selectors. It's here where I get a little confused, because the fader can remain topped and selection can be changed over to the switches. It would be my guess that you would have to lower and top the fader again in order to regain control with the mixer. I have yet to find an operational manual for one of these mixers. All of the information that I have for this comes from an engineering manual and a (of all things) clip from a Blue Peter episode. The engineering manual was found on which is a marvelous site for learning about all of the tech that the BBC employed on a very small scale (I mean down to the individual modules that make up consoles and apparatus). Unfortunately, no instruction manuals...

The Blue peter episode, reproduced below, gives a neat look into the gallery (or control room if you prefer) of TC1. It's a neat little clip, but for just the mixer, skip to the 5 minute mark.

According to the manual, the switcher also had the ability to put black borders around white captions or to synthesize alternate colors on them. Also, the ability to remove color for keying. In the Blue Peter video, you can just barely make out "overlay" and "background" on the two rows of pushbutton switches above the faders. Most of the labels on these diagrams from the manual are illegible due to the angle they were taken from and the black and white scan of the manual. To get the images look better and to be able to read the labels, I blurred the images a bit. These are the images you see here. I had to toggle between the two to trick my eyes into seeing the labels. This is what I was able to make out from the effects panel (click for a larger image:

bbc ep5-512 vision mixer effects labeled

It seems that the rows of knobs go in line with the rows of switches, so despite not being able to see their labels, I figure the knob above amplitude is a positioning knob for the captions and then some other knob that seems labelled 1,2,4 and 8). Softness is a switch I figure- "four degrees of hardness" the manual states. The rest, I have not much of a clue. The top right seems to start with "limit" but I doubt that its the control for the mixer's limiter. It's really interesting to figure though, that the mixer has such comprehensive controls for something kind of almost trivial- caption coloring. The wipes are quite neat though, and this view gives a great view of the pluggable modules. There are none installed on the Blue Peter program. Oddly enough, in this diagram, the color selected is light yellow text with a red edge.

UK TV studio History has some neat stories about this mixer, but not too much. As a matter of fact, there's not much out there at all for this mixer. It's weird though, because it was a very long lasting mixer, surviving from the dawn of color almost to the end of the EMI 2001 (although was most likely phased out sooner in the mid 80s)