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In Reply to: Accumulating noise posted by homer on May 05, 2002 at 05:57:32:
Hello -Not to be contrary, but you do seem somewhat argumentative:
1) I have never talked about noise performance. My posts were regarding the linearity of the DAC output.
2) I have never talked about dither. To the best of my knowledge, no video DACs employ dither, although this might not be a bad idea.
3) You are right that it makes more sense to use one set of video DACs for all sources. But until you can purchase an SDI-out equipped VCR or HDTV tuner, we will have to live with that redundancy.
4) Even in you turn the (unrequired) digital processing off, you are paying the penalty of a higher cost for the unit.
5) You will still achieve better overall performance, and at a much lower cost, by making picture adjustments in the analog domain, for the reasons noted in my previous postings.
Best regards,
Charles Hansen
Follow Ups:
> Not to be contrary, but you do seem somewhat argumentative:Perhaps, or maybe persistent and just a little slow, sometimes. ^_^
> 1) I have never talked about noise performance. My posts were
> regarding the linearity of the DAC output.Oops, my bad.
> 2) I have never talked about dither. To the best of my knowledge,
> no video DACs employ dither, although this might not be a bad
> idea.I was talking about dithering the results of any processing down to the precision of the DAC. My assumption is that any digital processing would accumulate up to like 32 bits of precision per sample, and then you would dither this down to like 12 or 14 bits, probably either in software, an ASIC, or a FPGA, just before sending it to the DAC. It's especially good, if the first thing you do is oversample the signal. Then, dithering has the advantage of moving even more of the quantization noise, introduced by processing, outside of the signal band, where the analog-domain filters will get rid of it.
> 3) You are right that it makes more sense to use one set of video
> DACs for all sources. But until you can purchase an SDI-out
> equipped VCR or HDTV tuner, we will have to live with that
> redundancy.You mean DVI-out, right? SDI is only a studio thing, and its lack of support for any encryption protocol will mean that it will stay that way. Audio and control are also lacking from SDI, but that alone wouldn't have kept it out of home theater equipment.
BTW, I can personally attest to the inadequacy of 8 bit video. I once looked at some gradients on an SDI monitor, and the quantization artifacts I got, with 8 bits per sample, were as clear as day!
> 4) Even in you turn the (unrequired) digital processing off, you
> are paying the penalty of a higher cost for the unit.Eh, it could be built into an MPEG decoder virtually for free, or done purely in software. It's orders of magnitude computationally simpler than a good line doubling algorithm.
However, I was speaking purely on the basis of performance.
> 5) You will still achieve better overall performance, and at a
> much lower cost, by making picture adjustments in the analog
> domain, for the reasons noted in my previous postings.Okay, beyond the purely theoretical level, I have very little knowledge of analog circuits, so I'll certainly take your word for it.
Anyhow, it sounds like we basically agree on everything, except those which I don't understand. ^_^ Thank you for taking the time to share so much valuable information!
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