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622 HDMI worse than component

Discussion in 'DISH™ High Definition Discussion' started by knealy, Apr 25, 2006.

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  1. jsanders

    jsanders Hall Of Fame

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    Doesn't HDMI have a handshake mechanism, and checksums to make sure the bits are correct? If your HDMI hits the maximum length, it can be repated. The differences between analog and component is where does the D/A conversion happen. You had better set the output on your receiver to do the native resolution of your TV so that it doesn't scale twice. If you don't, it will rescale, *regardless* of whether you are using component or HDMI.

    There are plenty of plasmas out there that do 1024x1024, but there are ones out there that do 720p native resolutions. While what you said may be true of some plasmas, it is not true of all plasmas. Under the scenario of a 1024x1024 plasma, regardless of what you use, component, or DVI, the TV will still have to scale a second time if the source mode doesn't match the output mode of the receiver. It is moot point.

    You should learn more about MPEG compression before you try to explain it. The Motion Picture Encoding Group (MPEG) compresses the signal with a Discrete Cosine Transform which puts as much information in the left hand corner of the screen as possible. This reduces spatial redundancy. The compression technique you are speaking of is very rudimentary and not nearly efficient enough to do the job.

    With dish's compressed up the wazoo SD signals, there isn't enough information to do a good job scaling the picture. Oddly enough, I've found that using the composite cable on the compressed SD picture works well, and precisely because everything gets combined and things get smeared a bit. The result is that smeared colors look better to me than blotching and solarization.

    Aside from what you have said TechnoCat, olgeezer was correct in what he said.
     
  2. saweetnesstrev

    saweetnesstrev Godfather

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    HDMI looks alot better then Component on my 411,, HDMI much sharper and brighter and bolder..
     
  3. jsanders

    jsanders Hall Of Fame

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    Can you show me where the original poster said that??
     
  4. olgeezer

    olgeezer Guest

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    I hoped what I said wasn't confusing. It apparently was. I just google the first article that popped up from Ecoustics and am pasting their take on what I thought I said:

    "The upshot of this article--in case you're not inclined to read all the details--is that it's very hard to predict whether a digital DVI or HDMI connection will produce a better or worse image than an analog component video connection. There will often be significant differences between the digital and the analog signals, but those differences are not inherent in the connection type and instead depend upon the characteristics of the source device (e.g., your DVD player) and the display device (e.g., your TV set). Why that is, however, requires a bit more discussion"
     
  5. SaltiDawg

    SaltiDawg Active Member

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    It is two different STB's. Are you are suggesting that all STB's when presented with the same (compressed) satellite data stream provide identical outputs?
     
  6. harsh

    harsh Beware the Attack Basset

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    Actually, with respect to non-CRT technologies, the video signal is digital until your brain processes what strikes your retina.

    Non-CRT displays all create varying brightness using your vision's perception of something that is flashing on and off very rapidly as being less bright than a continuous light with the same intensity. The ratio of on to off determines the relative brightness.

    It is likely that the only analog processing taking place is in the audio subsystem.

    Don't even bring up the concepts of photons and lightwaves.
     
  7. jsanders

    jsanders Hall Of Fame

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    I don't understand why so many on this thread are having trouble with these concepts.

    The 921 and 942 and 622 receive the same satellite data stream.

    The 921 and 942 and 622 have the same MPEG-2 decoding algorithm, they all use the broadcomm chipset to do it.

    The 921 and 942 and 622 all spit out the same MPEG-2 decoded bits through the DVI/HDMI outputs, provided that they are all set to the same output resolution. This is because these are digital outputs. It puts out numbers, and it is uncompressed, not MPEG-2 compressed.

    The 921 and 942 and 622 will have variations from each other on their component outputs. This is because they all go through unique, biased, DACs (Digital to Analog converters).
     
  8. LtMunst

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    This is what the post in question said "Actually, I think this is only true if the display is CRT based. LCD, Plasma, DLP, LCOS, etc wouldn't need a conversion to analog,
    ..."

    As I said, he was simply stating that the LCDs/DLPs etc did not have to convert the digital signal to analog in order to display. You then went off on the tangent about there ALWAYS being a D/A conversion when light is emitted.
     
  9. jsanders

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    Harsh, you don't even know the word for what you are describing. The "ratio of on to off" is called a "duty cycle".

    However, that isn't how LCDs work.

    You have a florescent back plane, which emits light through a polarized piece of glass. This emits white light. There are thin film transistors in groups of three (red, green, and blue) which make up each individual pixel element. These transistors cause liquid crystals to untwist, the amount of untwisting correlates to the amount of light which is allowed to pass through. Doing this will give you the hughes of red, green, and blue which make up the desired color of the pixel on the screen.

    Here is a question for some in this thread....

    How do you take the incoming numbers from the HDMI/DVI signal, and use those to control the individual transistors which allow filtered light to pass through the screen? You use a Digital to Analog Converter (DAC)!

    What comes out of your TV really is analog. Digital TV doesn't mean digital out. It means it is receiving a digitally broadcast signal!
     
  10. LtMunst

    LtMunst Hall Of Fame

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    What makes you think the scaler is the same for all 3 receivers?? Those receivers all add some level of processing to downscale/upscale the signal for whatever output resolution the box is set to. There is alot of variation in the way different scalers will process identical streams. To insist that all 3 receivers must process and output the HDMI/DVI signal exactly the same is not necessarily true.
     
  11. LtMunst

    LtMunst Hall Of Fame

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    Where do you get this DAC idea for LCD's, etc??? There is no DAC in these systems. The processor uses digital instructions to determine which parts of the LCD matrix to send voltage to as well as how much voltage to apply. There is no analog wave used in this process.
     
  12. jsanders

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    Okay. David_Levin said that in post #11. He isn't the "original poster" (your words from post #20), knealy is the original poster.

    The tangent was started when you disagreed with me in post #13 by stating:
    That isn't true. It has to do a D/A conversion when it sends displays the pixel. I explained how that happens for LCDs in post #29.
     
  13. jsanders

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    It appears you don't know what digital and analog signals are. You just described a digital to analog conversion process.

    Consider the transisitor loading curve.

    A transisitor can be used as a switch, or an amplifier. Let's take an old TTL circuit because they are very simple.

    When the transisitor is in saturation, above 1.5 volts, the switch is on. When the transisitor is below the base to emitter diode voltage (0.7 volts), the transisitor is off. Anything in between is undefined. That is the basis of the simplest digital signal.

    An analog signal is where the transisitor is used as an amplifier. The entire range of the transistor loading curve has distinct meaning.

    In the thin film transisitor (TFT) displays, the transistors that control the amount of light to pass through the red, green, and blue sub-pixels. The sub-pixels are being used as amplifiers, not switches. They are fed by analog signals!

    For your information, a digital signal switches things on and off. Voltages that exceed a threshold activate a swtich, and voltages below a different threshold deactivate a switch. There is also a histresis curve too, but that is a little more complicated.

    The analog signal is not set by voltage thresholds. The analog signal is what is controlling those transistors that act as amplifiers in the LCD display.

    If those transistors were digital switches, you would only get 8 colors because the transistors could only be on or off (no hues).

    You could get the following combinations of colors because each sub-element only switches on or off:

    red (off) + green (off) + blue (off)
    red (off) + green (off) + blue (on)
    red (off) + green (on) + blue (off)
    red (off) + green (on) + blue (on)
    red (on) + green (off) + blue (off)
    red (on) + green (off) + blue (on)
    red (on) + green (on) + blue (on)

    You need more than just switches to get your millions of colors that are detectable to the human eye. You need to control intensity of each sub-pixel. In order to do that, the transistor needs to act as an amplifier. In order to do that, the transistor sub-pixel needs to be fed an analog signal.
     
  14. jsanders

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    They all use the same broadcom chips in those receivers. Most likely, they all have the same scaler. It would be less likely if the receivers were not all from the same company, but in this case, they are!

    For arguments sake, why not just take the scaler out of the picture. ABC outputs in 720p. Have the receiver ouput 720p to your display. Under that scenario, no scaler is used. The people that are complaining will most likely still complain about their pictures looking different.

    The problem is likely that they don't have their inputs calibrated properly.
     
  15. LtMunst

    LtMunst Hall Of Fame

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    This is really a semantics debate. What you describe is not the common definition of a DAC. A DAC as most define it would convert the digital video signal into a complete analog wave. This is not done in LCD/DLP etc. By your definition, virtually every process within a computer would be a digital to analog conversion. Writing from RAM to the Hardrive would require a DAC since variable voltages are required to move the write arm across the platter.
     
  16. LtMunst

    LtMunst Hall Of Fame

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    Ok..leaving out the scaler. There are differences in the Video drivers. Same chipset or not, the software video drivers play a large role in the final output. If you think the video drivers are identical in these receivers, you are absolutely wrong.
     
  17. knealy

    knealy Legend

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    OK, here's the original poster back to see the fray that I've started.

    First let me say that I'm using the same pair of eyes to evaluate what I'm seeing, so getting them examined might improve my sight, but shouldn't change my comparison (unless someone wants to go off on a tangent on this as well!).

    Second. I'm not arguing about the technologies. I'm merely observing what I see. If anyone wants to tell me what I saw was impossible, then fine, but that's what I saw.

    Third. I was indeed comparing the DVI output of the 921 with the HDMI output of the 622. The component outputs of both receivers produce comparable results, -neither noticeably different from the other. But the digital outputs look markedly different even though they are connected to the same input on the TV (which BTW is a SONY Grand Wega KF-42WE610 LCD Projection HD Monitor - sorry for leaving out that info to start with).

    I tried different HDMI cables. I tried adjusting the picture settings on the SONY. While I can improve on the picture quite a bit by adjusting brightness, contrast, sharpness, whatever, on the SONY I can't get the brilliant and well defined images with my 622 that I got with my 921 (which had plenty of it's own troubles, as we all know).

    My only conclusion is that the 622 is doing something different than my 921 did since they're getting the same source material. The choices left to me are that they are indeed different in their outputs or I'm crazy. I choose the former.

    Hope I didn't waste all of your time. And I wish people could keep their comment civil.
     
  18. knealy

    knealy Legend

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    BTW, I hate it when technical people tell me what I'm looking at is impossible or not true. I'm here looking at it. Who are they to say what I'm looking at. It may be that I'm misinterpreting it, or looking at something different than what they think, but please don't tell me what I can see and you can't.
     
  19. jsanders

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    No, it is not a semantics debate at all. You do not know what an analog signal is when compared to a digital signal. A DAC can be used in anything, video or otherwise. It is this analog wave that you speak of which controls the three red, green, and blue transistors that make up a pixel in your tv.

    I guarantee you that a DAC is used in an LCD TV screen. If it was all digital, you would have two to the power of three, or 8 colors because you would only have three switches instead of three amplifiers. If your TV only shows the 8 primary colors, then great. If not, you have a DAC in your TV!

    Writing and reading RAM, or ROM involves purely digital signals. Why? Because these signals have only two states to them. A 'zero' is less than 0.7V, and a 'one' is a voltage greater than 1.5 volts. That is using the old TTL logic of VCC being 5v. To reduce power and heat, they have improved on this and reduced all of these thresholds. A digital signal is defined as a signal with detectable voltage states which are defined by thresholds.

    Writing to a hard drive does have some D/A conversion in it. In fact, it is a very complicated process. The digital signal tells the drive controller what sector it wants to go to. Then, there is an automatic control loop that moves the head accross the platter. They typically use something like a 9 pole filter to control that drive head quickly and produce a critically damped response. That is what they have to do in order to get the "seek time" spec on the drive.

    You are very wrong on this topic LtMunst. If you want to learn how it works, we can continue to the discussion. If you still think you are right, then please tell us how you think it works. How does the TV convert an uncompressed digital video stream of zeros and ones into the millions of colors of light that you see on your tv screen? Do you design TVs or computers or something? I haven't heard your explanation yet. Please tell us how it works, I would like to know.
     
  20. jsanders

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    Video drivers have nothing to do with this. The video driver is what allows the 921/942/622 to put menus and program guides and such on the screen. If the receivers are just doing video playback, then the video driver isn't used and the MPEG-2 decoder output spits right out the HDMI/DVI port. The driver is just an interface between the application running on a computer and the display controller.
     
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