On Tue, Jul 19, 2011 at 4:35 PM, Grant <emailgr...@gmail.com> wrote: > ... >>> >>> I still think it's a driver problem. Again: it's *physically* >>> >>> impossible to >>> >>> have these problems with the HDMI signal. At most you get "digital >>> >>> noise", >>> >>> which means some pixels get stuck or are missing. But not what you >>> >>> get; that's just something that can't be explained. >>> >> >>> >> I was thinking about this. The digital HDMI signal must be converted >>> >> into an analog signal at some point if it's being represented as light >>> >> on a TV screen. Electrical interference generated by the computer and >>> >> traveling up the HDMI wire should have its chance to affect things >>> >> (i.e. create weird shadows) at that point, right? >>> > >>> > Not with DFPs. Those work digital even internally. I assume of course >>> > that his HDMI TV *is* a DFP. >>> >>> But at some point the 1s and 0s must be converted to some sort of an >>> analog signal if only right behind the diode. A diode must be >>> presented with a signal in some sort of analog form in order to >>> illuminate, right? >> >> no. >> >> If your tv is a standard flat panel, the sub pixels only go from on to off >> and >> back. Nothing else. There is no analog signal, no transformation nothing. And >> off means 'let light through' and on 'black' > > Every digital signal is encoded into an analog signal. I think it > would take some serious EMI to sufficiently change the characteristics > of an analog signal so as to create an error in the overlying digital > signal if that signal is traveling along a wire. I can imagine it > happens but I would think it's rare. Even if that signal were > altered, I would think it just about impossible that anything but an > error could be produced. > > Whether an LED is on or off is determined by whether or not it is > forward biased. Biasing is established by analog voltages and/or > currents, and those can be altered by EMI. Again, I would think it's > very rare that EMI could affect an LED's forward biasing and change > its state from on to off or off to on. > > However, what color an LED emits is determined by the energy gap of > the semiconductor which is very much an analog process. How could it > be anything else? How do you tell a photon to emit a certain color by > feeding it 1's and 0's? There has to be at least one D/A conversion > somewhere between the digital signal and the emittance of the LED, and > that is the most likely point for EMI to affect the final output. > >> If you have an led display it is pretty much the same. All the levels you see >> are achieved with fast switching. There are no analog levels. >> >> Stroller is probably correct with overscan/underscan. >> >> But that has nothing to do with digital/analog conversion. >> >> >>> Digital is just a figment of our imagination after >>> all. >> >> emm, no, seriously not. > > It is though. It only exists in the conceptual world, not the > physical world. If you want to do anything with your digital signal > besides change it, store it, or transfer it, there must be a D/A > conversion.
You're thinking of PCM. (And that's what I was thinking of, earlier, too). I assume Stroller and Volker are talking about PWM, where a perceived analog value is achieved by rapidly turning a signal from full-on to full-off. (Yes, there's no such thing as pure-digital in the physical world. The confusion here appears to be in PWM vs PCM.) -- :wq
