another 'receiver as video switch' question

Discussion in 'Beginners, General Questions' started by Rich Sk, Nov 13, 2003.

  1. Rich Sk

    Rich Sk Extra

    Joined:
    Nov 18, 2002
    Messages:
    15
    Likes Received:
    1
    Trophy Points:
    0
    Instead of hijacking a previous posters post, I am confused by a reply made by Bob McElfresh about using a receiver as a video switch. Bob's reply to a post contained the following sentence:
    "While it's not a good idea to run Progressive/HD video through a receiver unless it is HD rated, it WILL appear to work. There will be a loss of focus and some other problems, but nothing will be damaged."
    Maybe I am missing something, but is it undesirable to run my Hughes HD satellite box output and my progressive scan DVD output to my Denon 3803 receiver and tell the receiver which video source to output to the TV? That was the first I have ever heard of a receiver being 'HD rated'. If there is such a thing, what do I look for in my receiver specifications that tells me that it is 'HD rated'? I am curious as to the answer, but it is too late for me to change my set up now so I'll be stuck my Denon video switch.
    Thanks.
     
  2. Harold Wazzu

    Harold Wazzu Supporting Actor

    Joined:
    Oct 1, 2003
    Messages:
    885
    Likes Received:
    0
    Trophy Points:
    0
    I think what he meant was you'll get a picture degradation if you receiver is not HD rated. HD rated is like 30Mhz or above for video bandwidth.
     
  3. Rich Sk

    Rich Sk Extra

    Joined:
    Nov 18, 2002
    Messages:
    15
    Likes Received:
    1
    Trophy Points:
    0
    Ok, now we are getting somewhere. If I look at the specs for the Denon receivers and find the following:
    Denon 1604:
    "2 sets component video inputs(30MHz), compatible with progressive DVD, DTV"

    Denon 3803:
    "2 Assignable component video inputs (100MHz), with On-Screen Display"

    Denon 5803:
    "3 sets component video inputs, compatible with wideband (480p, 720p, 1080i) response for progressive DVD, DTV (100 MHz)"

    I assume that the low end 1604 has the bare minimum required for handling progressive or HD signals. Based on the above, is there no difference when comparing my 3803 to the high end 5803 when it comes to video bandwidth capability? I assume not, and the statement 'compatible with wideband (480p . . . " that appears in the 5803 spec is attributable to the 5803 spec writers wanting to sound more high end than the 3803 spec writers. Thanks for helping to clear this up, or if it sounds like I have this totally wrong, thanks for making me more confused!
     
  4. Richard C

    Richard C Extra

    Joined:
    Nov 10, 2003
    Messages:
    22
    Likes Received:
    0
    Trophy Points:
    0
    Rich - you're really getting to the root of one of my questions also. I've seen the same specs you have, but I'm not sure they answer either of our questions.

    When they say "bandwidth", what do they mean? In the abscence of any other information, I assume they mean -3dB bandwidth. (The point where power is 50% of the peak and voltage is roughly 30% of peak).

    I also have read that 480p requires max bandwidth of 11.5MHz and 1080i requires max bandwidth of 26MHz.

    So, first order the inclination is to say "the AVR is spec'd at 30MHz, 1080i requires 26MHz, I'm good to go". But I'm not so sure.

    The things I haven't been able to figure out is how much dB drop you can have in the 11MHz or 26MHz band without degrading picture quality. I also don't know how sharply those component video inputs roll off to -3dB.

    Intuition tells me that 100MHz bandwidth likely means you are in the clear for a 26MHz signal. I'd expect any decent input to be reasonably flat (to the tenths of a dB) in that area. But, since I haven't seen graphs of dB vs. freq, I really don't know.

    Conversely, intuition makes me nervous that a 30dB bandwidth can accurately handle a 26MHz signal - but I'd think it's fine for 11MHz. But again, I don't understand how the bandwidth rolls off or how much flatness the signal requires before the degradation is noticeable.

    Maybe I'm making this too hard. (My RF radio background has me familiar with the concepts but totally out of touch with the context.) You'd think that Denon would design even the 1604 to handle 1080i bandwidth. But, even with a great company like Denon, I fear specmanship.
     
  5. Rich Sk

    Rich Sk Extra

    Joined:
    Nov 18, 2002
    Messages:
    15
    Likes Received:
    1
    Trophy Points:
    0
    I think I understand the issue here, but I don't know how the math works when you start talking about db drop and so forth . When I was in mechanical engineering school, I made a deliberate decision that I was not going to learn anything in EE301 class beyond V=I/R or whatever that Kircoff law is. My simple EE mind tells me that the more scan lines there are per frame (720 or 1080 vs 480), the more information that needs to be transmitted in a certain amount of time, and I'm assuming that this is related to bandwidth. Is it safe to say that the lower the bandwidth the receiver circuitry can handle, the harder it is to push a 1080i picture through the little tiny wires in the circuit boards and the picture suffers accordingly?
    Maybe we are travelling beyond the bounds of the HT basics forum and this thread needs to move to the display forum.

    PS. Now that I have jumped into the HT hobby, I'm finding this sort of thing pretty interesting, even if it does involve delving into the world of spark chasers. [​IMG]
     
  6. Richard C

    Richard C Extra

    Joined:
    Nov 10, 2003
    Messages:
    22
    Likes Received:
    0
    Trophy Points:
    0
    Rich - I'm with you. In EE school I made a deliberate decision to not retain any of my statics, dynamics and particularly thermodynamics. (That was also more than 20 years ago, so perhaps it's age and not deliberate.) Though you'd also fail EE301 now, what with you already forgetting ohm's law (V=IR) [​IMG]

    Your "simple EE mind" came up with a decent analogy. Yes, more information in a given timeframe requires more bandwidth. It's much more complex than pushing a picture through a circuit, but I think that's a good way to visualize it without getting into physics. Ideally, you also want the gain of the circuit to be "flat" during the band of information - if it's not flat some distortion occurs. However, in general you can compensate for some distortion by using certain techniques or modulation schemes.

    I'm just starting to get into this HT world as well. Someday I'll probably dig into how the data is modulated or transmitted. Right now I'm just trying to find out the same thing you are. Is 30MHz OK for HDTV, or do I need 100MHz? [​IMG]
     
  7. Bob McElfresh

    Bob McElfresh Producer

    Joined:
    May 22, 1999
    Messages:
    5,182
    Likes Received:
    0
    Trophy Points:
    0
     

Share This Page