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Question for Sylvia: Splitting AV output

Discussion in 'Hobby Electronics' started by DavidW, May 10, 2013.

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  1. DavidW

    DavidW Guest

    Dear Sylvia,

    Let's say I have a video device that has an AV output (3-socket RCA, for video,
    L & R). Can I connect it to the AV inputs of two other video devices (say a TV
    and something else) without loss of quality or blowing anything up? The
    connection would be done by having effectively two AV cables (with 3 plugs each)
    in parallel connected to said AV output.
     
  2. Brad

    Brad Guest

    Can I chip in here?
    Yes it will work, but perhaps not perfectly. It will depend on the
    performance of the equipment. The Video portion of the AV signal is
    1Vp-p across 75 ohms. Put two devices on that and you will see 0.5Vp-p
    across 37 ohms. The weaker signal may cause sync problems (less likely
    with modern equipment) and poorer brightness. The audio may similarly
    be lower, but you can turn the volume up to compensate. AV switch
    boxes are available cheaply, to prevent these signal losses.
     
  3. DavidW

    DavidW Guest

    Thanks. I thought it was probably a bit dodgy. I assume that a switch box (would
    splitter be a better description?) would require its own power supply, with
    transformer. I was hoping to avoid that.
     
  4. Sylvia Else

    Sylvia Else Guest

    Brad has summerised the issues, and I agree with him, except as far as
    the audio is concerned. In my experience, audio inputs have a relatively
    high impedance, and I would not expect the same problem.

    Beware of creating ground loops.

    Sylvia.
     
  5. DavidW

    DavidW Guest

    Probably better to ditch it altogether. For example, I don't want to have to
    adjust brightness between the split source and other sources. It all sounds too
    dodgy.
     
  6. Brad

    Brad Guest

    A switch box and a splitter are not the same thing. A switch box
    selects a different input or output, one at a time. A passive splitter
    will reduce the output. An active splitter contains an amplifier, so
    full output, but requires a power source.
     
  7. DavidW

    DavidW Guest

    I misunderstood then. I thought you were suggesting a "switch" that would solve
    the signal-loss problem while maintaining the two simultaneous connections. A
    passive switch was my first thought and what I'll probably go with, but parallel
    connections would be better for my purpose so I thought I'd ask.
     
  8. I bought a cheap plasticy switch on eBay so The World's Finest
    Grandson can connect his Wii when he visits without having to climb
    behind the furniture. Seems to work without any problems.

    --
    Peter Bowditch aa #2243
    The Millenium Project http://www.ratbags.com/rsoles
    Blog at http://peterbowditch.com/wp/
    To email me use my first name only at ratbags.com
    I'm @RatbagsDotCom on Twitter
     
  9. As Brad and Sylvia have said, you'll have issues with the video signal - not
    enough to prevent you from seeing it on both outputs, but more than enough
    to drag the video quality into the mud (remember making copies of copies of
    VHS tapes, and how good the resulting recording was?).

    If you have $47 to spare, grab this; it'll do the job properly for both
    audio and video, and has four outputs rather than just two;
    http://www.ebay.com.au/itm/121073559070

    If you want to save a bit of money and have a 12V power supply of reasonable
    grunt laying around (1A output should suffice), this one does just the video
    for $14; http://www.ebay.com.au/itm/261190349984

    Audio isn't a problem unless you're wanting genuinely high fidelity (which I
    suspect you're not); as Sylvia points out, most amplifiers have a
    comparatively high input impedance (generally several tens of kiloohms or
    higher), so there won't be any noticable signal degradation.
     
  10. Coach

    Coach Guest

    Very interesting topic. I have done exactly as the original poster has
    done and not noticed any loss of quality. But then again, I could
    never see what people were going on about HD tv because I could never
    really see the difference unless it was on a very large TV set. I
    would have thought that high def tv would mean we'd buy smaller TV's
    and sit closer to them, not buy bigger sets, Nobody seems to get
    that.
     
  11. Sylvia Else

    Sylvia Else Guest

    Some equipment has an automatic gain control on the video input, which
    would obviate most of the adverse effects. But it's not part of the
    spec, so trying it in a particular instance is the only way to know
    whether it'll work.

    Sylvia.
     
  12. DavidW

    DavidW Guest

    As an audiophile I do want hi-fi sound on one of the inputs (I have the option
    of directing its audio to a stereo amplifier and high-quality speakers for
    those movies/shows that are worthwhile having hi-fi sound). One of the reasons
    for my connection complications is that I prefer the convenience of the plain
    TV sound to watch the news or Biggest Loser, but it's not good enough for
    Raiders of the Lost Ark. (There are other issues too, such as whether I need a
    source to go to recording equpment.)

    Thanks for your suggestions. I hoped to avoid another powered device, but I'll
    consider it along with a plain switch.
     
  13. Jasen Betts

    Jasen Betts Guest

    it's an analogue signal therefore there will be some loss of quality.
    You won't blow anything up that wasn't already broken.
     
  14. Coach

    Coach Guest

    I always suspected you were one. My 6th sense is rarely wrong. Stay
    away from primary schools you sicko.
     
  15. felix_unger

    felix_unger Guest

    In that case you will need good quality audio leads. However no 'true'
    audiophile would want anything less than digital audio I would suggest.
     
  16. Sylvia Else

    Sylvia Else Guest

    True audiophiles recognise that digital is a quantised approximation to
    the true waveform, and that only analogue media are up to the task of
    faithful reproduction.

    Sylvia.
     
  17. felix_unger

    felix_unger Guest

    That's true of course for dedicated audio systems for music
    reproduction. However, when it comes to Audio/Video systems (surround
    sound 5.1, 6.1, 7.1) for watching movies there's no comparison in sound
    quality, if only for the fact that analogue audio is only stereo.
     
  18. Trevor

    Trevor Guest

    True idiots you mean, those that actually have a clue (perhaps not such a
    big percentage admittedly) know that after adding dither and a
    reconstruction filter, there is no quantitisation remaining, only a FAR more
    accurate signal than can be obtained by ANY analog recording method
    available.

    Trevor.
     
  19. Sylvia Else

    Sylvia Else Guest

    Of course, but you should never smarten up a chump.

    Audiophiles in the UK used to cite the BBC's Radio 3 (a classical music
    channel) FM service as the gold standard for analogue purity, blissfully
    unaware that the BBC was using digital technology to get the signal from
    its studios to the transmitters.

    Sylvia.
     
  20. Trevor

    Trevor Guest

    Nope, not for any modern digital audio system that isn't broken.

    I'd still prefer two HiFi channels to 7.1 low fi channels. Fortunately both
    can easily be HiFi, even if they often aren't.

    Trevor.
     
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