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DVI for HDTV

post #1 of 30
Thread Starter 
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
post #2 of 30
HDCP most likely, you need an HDCP compliant monitor...
post #3 of 30
Thread Starter 
Acer and Samsung monitors claim HDCP compliant. I though it might be that simple, but it doesn't appear to be.
post #4 of 30
What resolution(s) have you tried sending from the SA box over DVI to the monitors?
What resolution were you able to send from the Panasonic uint to the monitors using DVI?
post #5 of 30
Thread Starter 
The monitor shows a 1080 x 1960 resolution for the cable box and I don't recall what the DVR shows, but it isn't bluray so it would have to be 720P or 1080i I would assume.

Using a 4250 HD box and HDMI you get full HD on all the monitors.
post #6 of 30
Don't you mean 1920x1080 which is 1080i?
My PC monitor which has a DVI input will not accept any interlaced TV resoluitions over it's DVI interface.
You need to change your STB to always output 720p instead of 1080i.
post #7 of 30
Thread Starter 
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.
post #8 of 30
Most cable boxes that have DVI ports don't have the DVI activated. That would explain no picture.
post #9 of 30
Thread Starter 
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.
post #10 of 30
Is the charge for the 4250 HD box more than the 4200?
post #11 of 30
Thread Starter 
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.
post #12 of 30
Have you tried a different 4200 box? It sounds like the box is defective or the DVI is not activated.
post #13 of 30
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.
post #14 of 30
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.
post #15 of 30
Thread Starter 
Is there anything one can look at regarding specs to see if there is compatibility or any way to confirm or is it just that it works or it doesn't?
post #16 of 30
The Acer and Samsung have HDMI and a DVI (box) to HDMI (monitor) cable will work. So DVI from 4200 to HDMI on monitors did work? If that is the case the DVI is activated.
post #17 of 30
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.
post #18 of 30
Thread Starter 
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?
post #19 of 30
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.
post #20 of 30
Thread Starter 
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?
post #21 of 30
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.
post #22 of 30
Quote:
Originally Posted by Eaglescrest View Post

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.
post #23 of 30
Thread Starter 
But if I set my PC resolution to 1920 x 1080 how is that different from 1920 x 1080 from the STB?
post #24 of 30
There is a little thing called HDCP that you seem to keep overlooking.
post #25 of 30
Quote:
Originally Posted by Eaglescrest View Post

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.
post #26 of 30
Quote:
Originally Posted by Eaglescrest View Post

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.
post #27 of 30
Thread Starter 
Quote:
Originally Posted by Ken H View Post

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.

I tried four different units with the SA 4200. One was a Samsung 2333HD with DVI and HDMI and 1920 x 1080HD resolution. I don't recall if they claimed HDCP for the DVI, but calling their tech support could not get anyone who knew anything about HD connectivity beyond how to plug a plug in.

The second was an eMachines E211H which was 1920 x 1080 HD with DVI, but doesn't say anything about HDCP and again there was no ability to discuss with tech support.

The third was an Acer X223HBD with DVI which stated HDCP and 1920 x 1080 HD.

The last was Acer H233H BMID which has DVI with HDCP, HDMI and 1920 x 1080 HD. All four can produce picture with 1920 x 1080 output from the PC. None of the four could produce a picture with dvi to dvi connection from SA4200 STB (set at 1080i). The Samsung and H233H also have HDMI and could produce pictures with DVI (STB) to HDMI (monitor) connection.

A switch to a SA4250 which has HDMI Connector instead of DVI on the 4200 gave no picture on any monitor with an HDMI (STB) to DVI (monitor) connection, but did give picture with HDMI to HDMI on the two that could accept it.

Lastly, DVI out from Panasonic DVD recorder to DVI on H233H works.

So the problem seems to be getting an HD signal from Cablevision to a DVI input. Is it possible that there is something in the signal from Cablevision that is causing this or is it only the Scientific Atlanta box that could be at fault.

Cablevision claims that DVI on 4200 works and there should not be any issue but has no one with enough tech knowledge beyond that and blames everything on video vendor.

None of the monitors give you options for setting resolution or refresh rates; they only play what is provided.
post #28 of 30
As I stated before there appears to be an incompatibility between the DVI output chip on the 4200 STB and with the DVI input chips on the monitors and there is no problem using the HDMI output chip on the newer 4250 STBs. This incompatibility causes no data to be transferred so the resolution of the data content or a requirement for it to have HDCP enabled does not even have a chance to be an issue.
post #29 of 30
Thread Starter 
Walford, the problem also occurs if I use a 4250HD with HDMI and connect that to DVI on the monitor. In other words there is no HD combination that will allow a Cablevision box to work with a DVI monitor connect, even though the monitor can produce a picture if you use the HDMI connector.

Ken D's comment "DVI video output into most DVI HDTV inputs is fine. It's when you use a PC monitor with DVI video that issues occur." Leaves me wondering why. If DVI works well with a TV why would a PC monitor be different. Other than a built in tuner they should be pretty much alike I would think.

Also DVI is a standard so if a PC puts out a DVI string then any DVI device should be able to receive it. It appears the problem is that problem is that the DVI standard is broader or looser or whatever and so you may not be able to replicate the receiving requirements of the output. Is this fair to say?
post #30 of 30
I believe Ken-H is on the right track in pointing out that 1080p/30 from a STB and 1080p/30 from a PC are not always the same and often you need to send 1080p/29 instead from a PC.
AFAIK your Panasonic Box unit is outputing 1080p/60 over the HDMI-DVI link
From the PC you then need to also try 1080p/60 or 1080p/59 over DVI.
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