In article  "Elmo P. Shagnasty"  writes:
>In article <7Xarj.943$qw4.485@trnddc02>,
> Wes Newell  wrote:
>
>> > Let's go back to the idea that "I can still watch a snowy analog
>> > picture, but I can't watch a blank screen".  When there's not enough
>> > digital information for the dumb computer inside the TV to decode
>> > anything into a picture, yet there is enough information in the analog
>> > picture for the human brain to decode a picture/sound and see the story,
>> > how is it that digital is better?
>> 
>> Because with digital, you won't be subjected to such trash.
>
>Are you paying any attention?  Did you actually READ?
>
>With digital, you are subjected to the on/off, the dumb computer in the 
>television either has enough info or doesn't have enough info, period 
>syndrome.
>
>But the human brain is far beyond that, and can easily pick out the 
>story in a snowy analog picture.

  No, this is not true.

  Analog TV is an AM signal, and subject to threshold in a manner similar to
FM.  I don't remember the exact value, but I think it was a bit over 10 dB
carrier / noise for the signal bandwidth.  Less than that and you get nothing
worthwhile.

  Even if you are detecting the signal, if you don't have enough for
the set to lock on to and syncronize with horizontal and vertical sync,
you won't integrate the bits of signal to an image.

  The sound is FM, and needs 10-13 dB c/n to get a useful bit of audio.
Fortunately, it is across a narrower band, so it might be easier to do that.

>Digital TVs don't change that one bit.

  Do you have a counter-example of actual stations operating at the same power
on similar channels (such as adjacient UHF channels) from a common location,
where the analog is present but the digital is not?

	Alan

In article <fooh3l$a5v$1@news.Stanford.EDU>, Alan wrote:
> >With digital, you are subjected to the on/off, the dumb computer in the 
> >television either has enough info or doesn't have enough info, period 
> >syndrome.
> >
> >But the human brain is far beyond that, and can easily pick out the 
> >story in a snowy analog picture.
> 
>   No, this is not true.
> 
>   Analog TV is an AM signal, and subject to threshold in a manner similar to
> FM.  I don't remember the exact value, but I think it was a bit over 10 dB
> carrier / noise for the signal bandwidth.  Less than that and you get nothing
> worthwhile.

I don't understand what you mean by this. As an analogue signal fades, i.e. the 
RF level reduces, picture and sound become more noisy. There is no inherent 
physical threshold at which it suddenly disappears; the effect is gradual, and 
the point at which you regard it as too noisy to be watchable is entirely 
personal, depending on the interest value of the programme content and your 
tolerance level.

It's digital transmission systems that have a threshold, because they depend on 
the ability of electronic circuits, not a human brain, to be able to make 
something valid from the signal. As a digital signal fades, there is a definite 
level at which it is so noisy that the circuitry loses the ability to decode it 
and the viewer/listener is suddenly confronted with no picture or sound at all, 
after absolutely no warning that this is about to happen.

Sometimes, depending on the viewer(s), and depending on the content and 
significance of the programme, even a very bad picture can be more acceptable 
than no picture at all.

>   Even if you are detecting the signal, if you don't have enough for
> the set to lock on to and syncronize with horizontal and vertical sync,
> you won't integrate the bits of signal to an image.

The relative amplitudes of picture and sync in an analogue video signal were 
chosen with this in mind. The intention is that a typical timebase circuit will 
lose lock with the sync pulses at approximately the same signal level at which 
a typical viewer will lose patience with the picture. Again it's not a physical 
absolute, just the practical result of testing with real circuitry and real 
people, so anyone's individual opinion may vary slightly, but most of the time 
it holds true.

Rod.

In article ,
 Roderick Stewart  wrote:

> Sometimes, depending on the viewer(s), and depending on the content and 
> significance of the programme, even a very bad picture can be more acceptable 
> than no picture at all.

Just repeating that for those who refuse to acknowledge it.