I am re-reading this thread. I guess this was important to why TBC were not commonplace until the late 1980s:
Quote:
Originally Posted by ppppenguin
The problem in early TBCs was the ADC rather than memory. Until the TDC1007 was invented, 8 bit video ADCs were very complex and expensive. That chip won an Emmy aawrd in 1988. It was still several hundred $$$. Then the price of ADCs rapidly came down.
|
An article from 1987 reads:
Quote:
The chips that store the digital information are known as DRAM, for Dynamic Random Access Memory. Most of the current VCRs with digital effects use DRAM chips that each hold 256 kilobytes of binary data.
RCA's VMT-400 has nine, arranged to provide sufficient memory to hold two separate fields of color video data. Two of the DRAM's are dedicated to the picture-in-picture feature, while six more are used as the main memory for the freeze, mozaic and posterization special effects. The last chip is used to process synchronizing signals.
|
I don't think that in 1987 256 KByte chips were readily available. I think the author meant 256 Kbit modules. Looking at
John C. McCallum memory prices, I see 256 Kbit modules. If six modules are used to store a complete frame, then it is 192 KB for the whole frame. How? I guess they did not use the full Rec 601 frame, but a low-res one that would match VHS. Say, 480 * 240 = 115200 elements. With full 8-bit color it would be 115200 * 3 = 345600, this would not fit. But with halved color it would be about 170 KB, good enough for a freeze frame, but I suppose they figired it was not good enough for a proper TBC.
An interesting observation from the memory price data: in 1987 RAM price price was about $160/MB, but next year it jumped to $500/MB! It fell back to $120-180 by the end of 1989, but I think this spike spooked VCR manufacturers, so they scaled down on digital features. They probably also figured that PiP and clean freeze frame were not really popular.
By 1990 RAM price dropped below $100/MB. An article from 1990 was hoping for TBCs to become more common, claiming that "top decks adopt a picture-fixing feature".