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

[Michael Mol]

On Tue, Jul 19, 2011 at 4:35 PM, Grant <emailgrant@×××××.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