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Component routing question

Discussion in 'Cables & Switches' started by Abadd, Dec 12, 2003.

  1. Abadd

    Abadd
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    Getting a 434 tomorrow. I have 4 devices to hook up to my Plasma by component- Arcam 88+ and NTSC GC, XB, PS2 so I got myself a Audio Authority 1154 component box. Is there likely to be any advantage to putting the DVD player through my Denon 3803 receiver rather than the AA box? Probably a stupid question as I doubt there will be and noticeable difference but I thought i'd ask to see if anyone has the same kit. I don't like having to work such lovely signals through switchboxes.
     
  2. Nic Rhodes

    Nic Rhodes
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    It is all down to the bandwidth of the switching devices? Do you want me to expand?
     
  3. Abadd

    Abadd
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  4. Nic Rhodes

    Nic Rhodes
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    Every device has a bandwidth which can be measured. Bandwidth is not like a brick wall filter but a gradual degradation of the signal occurs as the bandwidth increase. It is quite difficult to do this however :) It is normally quoted as a -3dB value, which means the bandwidth at which the signal looses -3dB. -3dB is synonymous with 70.7% of the voltage and is also called the half power point. This is VERY visible / audible. Every video signal also has a bandwidth. For PS (PAL and NTSC) it is about 31 MHz.

    Now for you to be able to switch PS (PAL and NTSC) you need a minimum of 3x the DVD bandwidth in the switcher in order not to be able to see any loss(good rule of thumb). 3x will satisfy most people, 5 x is a more realistic figure for 'keen enthusiasts' and for the anal retentives I would use 10 x.

    For 95% of the population this means that any video switch needs to have a 100 Hhz capability if it is going to switch just PS signals. (3 x 31 Mhz). If you want to switch 1280 x 720@50 Hz (Bandwidth is 69 Mhz) you need a switcher capable of 207 Mhz (3 x) or 345 Mhz for 5x.

    Now if you satisfy all of the above will it work. Well no! Unfortunately it is not that simple, bandwidth is not a linear thing and one of the most important things is to get a REALLY linear first 10 Mhz bandwidth. Vitually no one quotes this bandwidth loss in the first 10 Mhz which is the most visible. This is why I hate the cheap SCART / BT25 switcher that many 'push' here. I have one of the latter, it is crap. This will be visible as 'smearing' and is exactly the same as people using incorrect characteristic impedance for their cables. See my stick post on this. If you find anyone quoting loss over the first 10 Mhz you know these guys know what they are doing :)

    You therefore need to know a little about the bandwidth each manufacturer quotes for their products. From memory I could not find an AA one and I think the Denon is about 100 Mhz. If you are switching interlaced or progressive scan DVD signals, the Denon should be fine, I can¡¦t comment on the AA.

    For info, until VERY recently all video switching on these receivers has a VERY low bandwidth, hence they screwed the signal and people complained. If you do the engineering correctly there is NO reason why they can¡¦t peacefully co exist with the ausdio signals and not interact. It was the just poor engineering.
     
  5. Abadd

    Abadd
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    Thanks for your help.
    I get the impression the AA is at least 100MHz so there shouldn't be much difference. If I were to route the DVD player through the receiver it would mean the consoles would have to go through both anyway and that can't be good.
     
  6. Nic Rhodes

    Nic Rhodes
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    Don't route through both devices if you can help it. Don't assume any device must be at least 100 Mhz, it rarely is :( If it is good, they WILL tell you :) Why not ask them, and insist on a -3dB figure. Anything else is cods wallop!
     

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