Re: [gentoo-user] Re: Problem with xf86-video-ati & nvidia-drivers

[Grant <emailgrant@gmail.com>]

>> ...
>>>> >> 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

Everything I said above applies to both PCM and PWM.  They are only
conceptual layers built on top of a physical/analog base.  PWM
switching from full-on to full-off and back is an analog process
representing digital data in order to represent an analog signal.

- Grant