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Originally Posted by Pete Deksnis
....ten years ago I worked on military stuff that used multiplying DAC's to contol what amounted to audio-frequency range levels; is that how the function is or was implemented in TV for audio gain, contrast, and whatever? Is it even a good question?
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It's a good question. There were no such things as multiplying DACs until much later. The first ICs for the color and video sections [and audio] were all analog, and did gain control using Gilbert-cell analog multipliers, which could be controlled by a common DC voltage. By the way, this was easier to implement cleanly, since the video and chroma signals did not have to be wired all the way to the customer controls and back, and the DC voltage could be filtered to get rid of noise pickup.
[Start of brag] One of my favorite inventions is a three-way I did with two other guys at Zenith (for monochrome chassis), where we stacked Gilbert cells, and using a simple external RLC filter as a simultaneous lowpass filter, differentiator, and second differentiator, did contrast control, switchable gated noise reduction, and video peaking control, in one swell foop [end of brag].