Timeline Analog 2. John BuckЧитать онлайн книгу.
nonlinear computer editing system.
The joint venture between Memorex and CBS Television, CMX Systems, transitioned from analog to digital. Group manager Ken Taylor hired more staff to design the control systems, digital circuitry, disk pack switching and user interface for the unnamed editing system. Jerry Youngstrom recalls:
Obviously we needed some sort of program to ‘run’ the system. Memorex had put in an IBM 360 computer to aid the hardware group but the only person in the media group that knew how to program it was a statistician. For that matter in the wider engineering community there was almost nobody writing code. Programming was a brand new discipline. We were exceptionally lucky to find Dave.
David (Dave) W. Bargen worked at the Medical Diagnostics Operation of Xerox Corporation on N. Halstead Street, Pasadena, California. He recalls:
A friend heard about the new joint venture between CBS and Memorex and told me before he left Xerox to work for Memorex.
Bargen started at CMX in May 1970 and among his first were to choose a computing platform.
I selected the DEC PDP-11 computer.
The PDP-11 computer, released just a few months earlier, had 16,000 words of core memory (16 bit), no hard drive and ran at 3 to 5 microseconds per instruction. (about 1000 times slower than a typical PC today).
The PDP-11 was a new computer model. It was 16 bit but also handled 8-bit bytes efficiently, which would be helpful for hardware control. It had good performance for the money. The original CBS system had used a DEC PDP-8, but that it was at the end of its model life-span.
Bargen went to Bill Butler and Ken Taylor with his recommendation. He recalls:
At the time it was the preferred mini-computer. DEC was the original mini and a huge success until the advent of the Apple and PC. The PDP -11 had adequate power and speed, and supported all the peripherals we needed, including a punch paper tape reader/writer and the graphic interface which was quite new at that time.
Bargen's next decision, software coding.
Assembly (language) was used because of the need for speed and the limited memory capacity of the day.
He now needed software coders, who were uncommon in the Bay Area.
James (Jim) C. Adams Jr. had moved from Fairchild Semiconductor to Link General Precision. Link had created flight simulators for the Apollo Lunar Lander (above) and then the F-111 fighter aircraft.
I was using an Xerox Data Systems (XDS) Sigma 5, developing the radar simulator software for the F-111. With this, and all of my previous jobs, I was sent to the factory schools to learn the software development process as well as the underlying hardware philosophy of the specific computer.
DEC for the PDP-8, Scientific Data Systems for the SDS 930, Xerox for the SIGMA 5, as well as others such as Control Data Corporation (CDC)for their systems and Texas Instruments for analog/digital circuit design. At XDS the key take-away for me was how to process interrupts. An interrupt is a signal sent by a device that it needs attention. This is very different from a processor interrogating a device periodically to see if it either has data or is able to receive data.
Adams soon left Link.
I answered an ad in the San Jose Mercury-News for a programmer 'to work on a new innovative system'.
Adams became the first outside hire by CMX. He adds:
Once onboard I met my immediate manager, Dave Bargen, I was introduced to the concept of video tape editing. Specifically, the process of many camera takes, selected parts of each take which were to be linked together to create a deliverable package.
The older technology was to cut the desired part out of the original take and glue it to another piece cut from another piece. The newer scheme involved using a frame counting code recorded on the tape and recording a number of frames from that point to another tape.This required two machines able to synchronize to the correct frame code for each machine.
This concept had been carried to a computer to perform this task, rather than a dedicated hardware device that was quite operator intensive.
Adrian Ettlinger’s proof-of-concept system, employing a PDP-8, could perform a single recording, but only the one segment buried in the computer program. CBS wanted to create a two-part system, the first of which was to determine the segments and sequence of the original takes at low resolution, what we now call Offline editing, and the second part was to copy the edit decisions onto a blank tape at high resolution for review and eventual delivery to the broadcast stations. What became known as Online editing.
Bargen adds:
The first product priority was development of the low resolution offline editing system that became know as the CMX 600, because that was the most innovative, and had the most unknowns.
Adams continues:
From a control viewpoint, the offline process was pretty straight forward. Each frame of the original material had a frame code associated with it; this code tallied hours, minutes, seconds and frames associated with the time at which it was originally recorded. This frame count information was penciled into the program script such that any segment of tape could be quickly located from the script notes.
The frame count codes came in two variants: straight 30 frames per second (fps) for the black and white low resolution video and a somewhat different method to accommodate the color video at 29.97 fps.
The complexity came with the desire to display the selected frames at other than 30 fps; faster, slower and frame-by-frame. A further complexity was that only the first field of each frame was on the disk, the second field for interlaced video came from an auxiliary disk which recorded the first field and delayed in a line-time to provide the second field.
Dave Bargen wrote:
King Anderson did much of the digital hardware design, for control and interface. Later, he headed the manufacturing of the products.
Jim Adams continues:
Dave had selected the PDP-11 as the computer to use in this system and I believe that turned out to be the best decision made in the entire project.This computer had many attributes of larger systems and the machine assembly code was extremely versatile.
Add-on (interface) boards for the PDP-11 were designed to link the necessary control features of the disk players, video switching circulatory and light pen position to the processor.
I was provided with a high-speed paper-tape reader and punch and an ASR-33 teletype for my software development.The printing speed of the ASR-33 is 10 characters per second.After a couple of months, I was able to persuade the company to get a Memorex printer which was about ten times as fast, but I still edited my programs on the ASR-33.
The analog team were still dealing with issues as Cal Strobele recalls:
I spent many days, in a fog, trying to figure out how to apply what we already knew about compression and recording to this project. In the end I came up with an idea to skip every other video field, in black and white and to record the audio on the back porch of the video for the missing field.
The ‘backporch’ is a term referring to the signal time between the horizontal sync pulse and the next active portion of the video