Analog tv's vs. Digital tv's (1 Viewer)

[BradD]

How does a digital television differ from an analog television?
Is there no analog converting what-so-ever?
What if there is an analog input signal?
Is the picture diplayed digitally?

 

[Scott L]

Only DLP and LCD TVs that offer a DVI input can display a purely digital signal, either from a DVD player, PC, or Satellite with HDCP DVI output.

 

[Thomas Newton]

"Digital TV" generally refers to equipment that supports the DTV and HDTV broadcasting standards. The broadcast signal format is digital, but that doesn't mean that all parts of the playback chain are digital (or should be).

A lot of the "digital TV" sets out there are actually high resolution analog sets. They have an assortment of analog inputs (composite, S-Video, component) and built-in tuners for the current NTSC TV standard. If the sets see a high-resolution signal on the component input, they can display it. This makes them HDTV-ready. Theoretically, you could plug in a HDTV tuner with component outputs, and get HDTV. I say theoretically because we've already seen boxes that degrade flagged signals to 480 lines of resolution -- the better to please Hollywood.

HDTV-ready sets generally have built-in line doublers (to minimize visible scan lines on regular TV broadcasts) and make nice monitors for progressive-scan DVD players.

Note that in "DVI-HDCP", the "-HDCP" stands for gratituous copy protection.

 

[BradD]

So then, would an analog tv set be a tv that can only accept and display a NTSC signal (i.e. 480i)?
And if the tv set can accept and display (converted to its natural resolution of course) 480p, 720p, or 1080i, then it would be considered a "digital tv set"?

 

[Scott L]

Brad it's really hard to say. It seems retail chains like Best Buy made the term "Digital TV" popular. Most of the HDTVs they sell are really just analog sets that sport high resolutions. So the unofficial definitions:

Digital - HDTVs

Analog - old NTSC sets

I wouldn't worry about it too much, HDTV is the money term we're looking for.

 

[Iver]

The magazines and other media outlets cause confusion by using the term "digital TV." This creates the idea that NTSC TV's are "analog" and ATSC-compatible TV's are "digital." However, these terms are misleading.

Most people would consider an LCD-based TV, whether direct-view, RPTV, or FP, to be a digital display. But such a TV can have an NTSC tuner and display analog NTSC broadcasts. Likewise, you can have an STB that picks up an ATSC digital broadcast (in any of the ATSC resolutions), which is then output via component analog connections and displayed on a CRT-based set. Or you can have an integrated H/DTV that tunes digital ATSC broadcasts and uses an analog CRT display.

It's most accurate to use the terms "analog" and "digital" to refer to various stages of the transmission and display chain.

Broadcasts can be analog (NTSC) or digital (ATSC), though HD broadcasts don't have to be digital. The Japanese intially have used an analog HD broadcast system.

STB digital tuners can output an analog signal at the resolution used by NTSC TV's. That will be neccessary, once the transition to all-digital goes through, in order for owners of NTSC sets to continue to receive broadcast TV. STB's can also output an analog signal at the higher resolutions. They can also convert an input resolution to a different output resolution (upconverting 480p to 1080i or downconverting 1080i to 480i, for example).

Recently, STB's have come on the market with digital outputs using the DVI type connections. Various displays have also recently become available with matching DVI inputs. Less commonly, the IEEE-1394 (a.k.a. Firewire, iLink) digital interface has appeared on source and display devices.

As already mentioned, up until recently most H/DTV's and H/DTV monitors relied on analog CRT display technology (found in direct-views, RPTV's, and projectors). As of late, digital type displays, using LCD, DLP, and LCOS technology, have appeared with direct-views, RPTV's and projectors.

 

[Thomas Newton]

In common usage, yes.

There's also what Scott was referring to -- which is the internal construction of the TV set.

A LCD display consists of a fixed grid of pixels. A DLP display, if I recall correctly, reflects light off a grid of really tiny motorized mirrors. In either case, the TV would address each pixel in much the same way as a computer addresses memory.

In a CRT-based TV, electron beams sweep across the tube. As they sweep across, the set changes the intensities of the beams to light phosphors on the tube's surface. Old NTSC sets don't have any computer circuits -- they drive the beams from the analog input signal and/or hard-wired electronics. A HDTV or HDTV-ready set might convert all input to digital form (for ease of line doubling, etc.).

 

[ChrisWiggles]

Yeah, this is EXTREMELY confusing, because the terms are all the same.

There are two things going on that need to be totally distinct (which they are not in common use, as most people don't know this detail)

First, Digital TV(ATSC) as opposed to analog NTSC.

Second, the display technology, Analog CRT, versus digital displays such as plasmas, LCDs, DLPS, etc.

Add to that complications with "digital chassis CRT" for digital control of the analog system, and things get DAMN complicated. Everyone thinks digital is the magic word. Digital is just *soooo* great no matter what, so everything is sold as digital this and digital that. I think it's easier if you ignore that all together, and figure out what signals you are dealing with, and what the TV is, and is capable of.

 

[BradD]

I appreciate the replies. Very informative. I believe I got it now.