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SDI vs DVI

Discussion in 'Projectors, Screens & Video Processors' started by joust, May 18, 2004.

  1. joust

    joust
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    I'm looking to set up a system in the future that will probably be based around a CRT projector running at 1280x720, fed from some sort of scaler (I could look at the PC route, but the missus would probably find iot too difficult to use). Now question is what sort of signal to feed to a scaler - SDI or DVI? What is the merit of each technology? Are they both kept in the digital chain in the DVD player, prior to transmission (I know that SDI is, as there is a direct feed from the MPEG decoder, how is DVI handled inside a DVD player)? Are there any great downsides to each of these formats?

    Your opinions as always are greatly welcomed.

    Cheers

    Joust
     
  2. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    not much time for full reply but forget DVI for your application. DVI froma decent DVD player will likely as not have HDCP copyprotection applied to its output. Any scaler that is capable of receiving this signal will turn off its analogue output as soon as it gets a signal with copyprotection from the DVD player. As virtually all DVD's are copyprotected you wont be watching much.

    SDI is closer to the signal on the disc and doesn't have any copyprotection. Use SDI if you are going to have a CRT projector

    Gordon
     
  3. loonatic

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    I am looking into getting my Sky+ and Denon 2900 SDI modded and going for one of the new generation of scalers.

    But I was just thinking - which is early in the morning for me so I'm probably wrong - but if you are taking the output direct from the MPEG chip does this mean that you bypass any output settings in the actual device. So for Sky+ for example would it ignore what setting you have for screen type 4:3 or 16:9 for example.

    If so this would be an added bonus as I still have a 25" 4:3 TV in the bedroom and I am fed up switching screen formats. I know I should replace the old TV but it's doing a damn good job.

    Cheers, Lee
     
  4. Nic Rhodes

    Nic Rhodes
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    G has said it all. SDI all the way in this application because of HDCP and the other reasons discussed here. It is just truer to the original.
     
  5. buns

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    I imagine that although the info for switching will be encoded on the signal from the mpeg, that most if not all of the video processors you could use will not actually use it and do switching. If im not mistaken, cybersoga brought this up on avsforum wrt the new lumagens

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  6. loonatic

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    I'll have a read through the AVS thread - started last night but it's a long one.

    I think you may have slightly missunderstood my question though mate. I am not talking about auto aspect swithcing but what I was curious about is if I have my Sky+ box set to output letterbox 4:3 with low contrast what output will I get from the SDI output ? does it ignore those settings and just output the raw MPEG stream or will it output a 4:3 letterbox formatted image ? Does that makes sense ?

    Cheers, Lee
     
  7. dgc

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    On a similar note to loonatic's qn...

    How much of the internal processing within the dvd player is bypassed via SDI? Is SDI an output of the digital signal straight from the disc or does it go through any processing stages first.

    To put it another way - would a £100 dvd perform as well as a £500 if both are outputting SDI?
    Presumably it still depends on the quality of laser? quality of internal hardware?
     
  8. buns

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    Ah sorry about that.... im not altogether sure what exactly the stream on sdi will be, i can tell you the colorspace but that is about it. I'd take a wild guess that the sky+ setting wont make much difference to anything.

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  9. buns

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    That is an ongoing arguement..... video wise many will argue that one player will be pretty much as good as another assuming equal quality of MPEG decoder though others feel that some of the more expensive players do perform better. Of course sonically, the more expensive player is likely to be better

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  10. loonatic

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    Perhaps you could let us know when you get yours up'n'running exactly how it behaves :thumbsup:

    My guess is that the SDI mod is stealing the output from the MPEG decoder before the Sky+ box has the opportunity to mess with it before sending it out via it's outputs.

    If this is the case then it's potentially an added bonus.

    Cheers, Lee
     
  11. buns

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    I believe thats pretty much the biggest bonus! The signal gets taken out of a device before the device's designers have a chance to screw it up!

    I will certainly let you know what it does as soon as its all here!

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  12. cybersoga

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    If SDI was a pure mpeg stream then you wouldn't be able to see the dvd player/set top box menu screens, OSD graphics etc... the fact is, it isn't, it's after the mpeg decoder but before the video DAC, which means your bypassing the analogue stage of the set top box, where there's more room for distorting the picture by using cheap components and poor design. You'r still at the mercy of the mpeg decoder, but there's far less to distort the picture compared with using the analogue video outputs.

    Regarding DVI vs SDI, SDI is best for dvd because it's closest to what's stored on the disc (8bit 4:2:0 is output as 4:2:2). DVI is 8bit 4:4:4, HDMI offers 12bit which is great for new HD video formats but not much use for DVD. DVI/HDMI has HDCP copy protection when the disc is copy protected which means it'll only work if all the kit is HDCP compatible including the scaler and the screen.
     
  13. David PluggedIn

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    Hi Lee

    In answer to your question, then the contrast settings of the Sky box *dont* affect the SDI contrast, just the analogue side. The aspect ratio is affected though in the normal way. So sort of half and half then :)

    cheers
     

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