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DVI for HDTV

6K views 29 replies 6 participants last post by  walford 
#1 ·
In stead of buying a larger flat screen at this time, I wanted to get by for a while using an HD monitor. I have tried three different ones, an e-Machines 21.5", Acer 23" and Samsung 23" Monitor/TV. All have DVI connectors and I got a DVI box (Scientific Atlanta 4200) from the cable company (Cablevision). None of monitors would work with this box. The Acer and Samsung have HDMI and a DVI (box) to HDMI (monitor) cable will work. So it would seem that the DVI on the monitors is the problem; however, attaching a Panasonic DMR-EA18 HDMI to the DVI input on the monitor works fine.


I am assuming that it is an issue with encryption, but does anyone have knowledge of where the problem really is? Cablevision is, not surprisingly, clueless.


Thanks
 
#2 ·
HDCP most likely, you need an HDCP compliant monitor...
 
#7 ·
That doesn't seem to be the issue here. The STB shows 1080i and the monitor shows 1920 x 1080i. But the HD is through HDMI instead of DVI. With DVI I don't get a picture, though the box states DVI is HDCP compliant on DVI.


In other words everything should work, but it doesn't.
 
#9 ·
That is a possibility; however, when I spoke with Cablevision's tech support people they claim that the DVI should work. If it were not operable then you would think they would know that. For HDMI you need a different box, so it wasn't like they may have thought I was looking to use HDMI and was using DVI.
 
#11 ·
There isn't a difference in charge, but this is a knowledge issue rather than just trying to solve a problem. I know I can get HD with the 4250 and HDMI on monitor; I want to understand why I can't get HD with 4200 and DVI. Cablevision says I should be able to do so, but it hasn't worked. Monitor manufacturers don't have an answer. Both sides blame the other and nobody has the knowledge to help.


Manufacturers put trained monkeys in tech support position. Even the US based ones have no tech know-how. Someone at Samsung tried to tell me that DVI is an audio only connection. So I am trying to troubleshoot myself to understand why something that should work doesn't.
 
#13 ·

Quote:
Manufacturers put trained monkeys in tech support position. Even the US based ones have no tech know-how. Someone at Samsung tried to tell me that DVI is an audio only connection. So I am trying to troubleshoot myself to understand why something that should work doesn't.

The DVI is not activated. You already know that the monitor folks hire trained monkeys, as does Samsung, so what makes you think the same isn't true with cable companies? 28 years in the industry, and I'm telling you that the DVI port on most cable boxes IS NOT SUPPORTED.
 
#14 ·
The DVI interrace specifications are no ways near as tight as the HDMI specifications.

There have been several examples over the years of DVI-DVI and DVI-HDMI interface conections that did not work due to different vendor implementaions of the DVI interface specs especialy when longer cable lengths and or HD resolutions(720p, 1080i) were involved.
 
#17 ·
With HDMI there is a very extensive testing lab that almost all/if not all vendors submit their HDMI products to for compatibility testing. AFAIK there never was as correspoding test lab for DVI products so if a vendors product did not meet the specs nobody including the DVI vendor knew.
 
#18 ·
Thanks all for the thoughts and comments.


From Walford's comments I can only conclude that DVI has to be treated as a worthless connection. That doesn't mean that it can't and doesn't work, but that when evaluating it you must ignore it in the analysis of a product/setup and be very happy if it in fact does give usefulness.


This seems to be the norm for TV connections; however, I don't understand why DVI seems to be so dependable for computers, but not for TV. Is it because TV set top box vendors didn't follow the standards that computer video vendors did?
 
#19 ·
All the DVI interface chip vendors thought that they followed the specs correctly, however, there were some spec tolerences rrequirements minunderstood. This along with the fact that there was no testing lab to validate their implementations.

Also PC have done better with DVI when used with PC monitors that accept PC resolutions over either VGA or DVI.

STB's do better with DVI or HDMI with HDTVs since they are primarily used wiith ATSC digital TV resolution standards.
 
#20 ·
Walford,


I guess this is what I don't understand. Is DVI a different standard for PC than cable set top boxes? I can get 1920 x 1080 from my PC card to monitor by dvi to dvi connection, but I cannot get that same resolution to work with the same monitor if the source is a Scientific Atlanta 4200HD dvi to dvi connection. Where is the problem? The SA 4200 isn't generating a compatible signal?
 
#21 ·
The resolutions used by PC monitors such as (SVGA)800x600@60HZ and 1024x768@60HZ(XVGA) are not the same as the resoloutions for TVs broadcast signals such as 480p, 480i,720p, or 1080i.

Only very recently have display with DVI or HDMI interfaces which have DVI or HDMI interface connection chips which can accept both PC resolutions or TV resolutions.

So, yes the resolution standards used by STBs for TVs and the standards used by PCs for PC applications are different.
 
#22 ·

Quote:
Originally Posted by Eaglescrest /forum/post/18142376


I guess this is what I don't understand. Is DVI a different standard for PC than cable set top boxes?

Yes to a great degree, due to the differences between HD video formats and PC video formats, and HDCP issues.
 
#25 ·

Quote:
Originally Posted by Eaglescrest /forum/post/18143290


But if I set my PC resolution to 1920 x 1080 how is that different from 1920 x 1080 from the STB?

For one, the 1920x1080 STB output is interlaced. The 1920x1080 PC output would normally be progressive.


You can in may cases configure PC video output for use with a standard HDTV. For 1920x1080i set the scan mode to interlaced and the frame rate per second to 29.97 or 30.


Or, try 1920x1080p (progressive) at 23.976, 24, 29.97, 30 fps.


Most current HDTV's will automatically accept PC video formats, but most PC monitors will not accept HD video formats.


And, PC video does not use HDCP. Video formats over DVI or HDMI do.
 
#26 ·

Quote:
Originally Posted by Eaglescrest /forum/post/18133691


Thanks all for the thoughts and comments.


From Walford's comments I can only conclude that DVI has to be treated as a worthless connection.

Not necessarily.


DVI video output into most DVI HDTV inputs is fine. It's when you use a PC monitor with DVI video that issues occur.
 
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