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Does it matter if optical cable is to long

Discussion in 'Cables & Switches' started by Dextur, Sep 15, 2004.

  1. Dextur

    Dextur
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    Hi

    I have a distance of onlly 1.8 metres from my DVD to amp, using a digi optical connection, however I have a 5 metre cable, does this matter that it's much longer , are these the kind of cables that should be pretty much the exact length they need to be or you get signal degredation.

    I'm guessing seeing as this stuff sort of goes 50 miles in exchanges this is not a problem. but not entirely sure it's the analagy works , is it the same stuff?

    Also does it pay to really spend on optical cables or is a £15.00 much the same to the averager home cinema user as say a £50 one?
     
  2. pjclark1

    pjclark1
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    TOSlink and digatal coax cables
    I had my digital cable only 1/2 plugged in, most of the time it was working
    A few times the big blue light on my amp winked out, and a big CLUNK as the speakers muted. Plug it in and it works.

    You don't get signal degradation on digital. It's working, or it isn't

    £15 !!! ARE YOU INSANE ???
    1.5m TOSlink cables are 99p each on ebay and work perfectly (when plugged in fully DOH!)
     
  3. Dextur

    Dextur
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    Cheers PJ

    ps £15 is very cheap compared to some ToS cables I have seen online. check out QED etc, wowza!!!
     
  4. CDphobe

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    Is this for real or a Troll?? Of course you get signal degradation on digital, but when information goes missing between transport and DAC (for example) then the DAC "guesses" what the answer should be, so you still get an output. When it gives up and the speakers go CLUNK then even the wonders of modern computing haven't been able to guess. PLEASE don't fall for the "perfection or nothing" myth, its just as truthful as the "CDs are indesctructable in normal use" myth. Would you be happy knowing that a piece of electronics is guessing what your source should sound like? If not, get a decent cable and plug it in properly.

    Simon, to get back to your question, I can't speak with any authority on optical cable so I'll not even try, I've never used optical interconnects. But I can confirm that there are audible differences, checked in blind A/B listenings, between different digital cables. That's not to say that a £50 cable will be better than a £15 cable, there's more to it than the manufacturer's retailing strategy. A well made cable using sensible materials will outshine a bad choice of cable which is poorly made using nice looking phono plugs that sells for a lot more.

    But with any form of interconnect, the shorter the length, assuming that you don't then stress the cable, the better. Most people view this as "less resistance" or similar for a metallic conductor, but there are also a range of other more significant problems such as antenna effects that are alleviated by shorter lengths (unless you just happen to pick a multiple of the half wavelength of a nearby transmitter - ask anyone living near an airport). For optical cables, antenna effects are not an issue, but every bend of the fibre optic material will result on some dispersion and internal reflection of the light signal, and I'm guessing your 5m cable is coiled up. I don't know if this has any significant impact, I'm talking only about the physics of the system, as I am given to understand them. With any luck someone with real world experience of digital optical cables will be along shortly.
     
  5. pjclark1

    pjclark1
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    CDphobe
    If anything is guessing on a significant bit then it would be easy to hear.
    What a load of nonsense people talk about cables. Lets compare experience
    and see who is most likely to be correct. I am basing my answer on a degree in
    electronic engineering, and 8 years working as a studio sound engineer in broadcast
    television. Not once did anyone in the business discuss buying better quality audio
    or video leads, & I must have been involved in about 10 studio refurbs during that time.
    The only cable concerns ever mentioned was when using balanced mic lines which are subject to crosstalk, if you get it wrong, but nothing to do with cable quality and more
    to do with cable routing. We ran cables far in excess to anything in the home envronment using 100m rolls of video cabling just to adjust video timing errors. The signal that went in is what came out.
     
  6. CDphobe

    CDphobe
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    An interesting couple of comments there PJ.

    First, given your experience, I'd have been far too embarrassed to admit failing to plug a cable in properly, my hat goes off to you for that!

    Your experience in broadcast I would suggest bears out my earlier post though - that specifying the correct material properly made is by far the most important consideration for cable. Professional studios and installers would use the correct material as a matter of course, and not resort to some of the snake oil tactics one can see in the domestic hi-fi arena. I'm not suggesting that people should spend a fortune, but I do believe that there are audible differences based on the QUALITY of the cable, not the price.

    You specifically mention balanced mic cables, again precisely the point I was making previously, its often the impact of external signals that make the difference, and so shielding or the use of balanced cable, is important. Most domestic systems don't use balanced connectors due to the size requirements for the traditional XLR plugs and sockets (Linn being one obvious manufacturer that flirted with XLR on their LK1/2/275/280, but utilising a single XLR in unbalanced mode for both channels) so again it comes down to specifying the RIGHT materials.

    My point remains though that digital is NOT either working perfectly or not at all - I recall that in the very earliest days of domestic digital audio a well respected manufacturer that was selling a 2 box Transport and DAC actually offered a third box to monitor the DAC to show the volume of "correction" that was being applied. Obviously the biggest correction levels occurred when a dirty CD was used, but there were identifiable, and repeatable, differences when different cables and lengths of cable were used too. None of this however directly helps Simon's question.

    Al
     
  7. Keiron

    Keiron
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    Just get the cheapest cable you can get. I've got 2 lengths of 10m optical joined in the middle. It works perfectly. Before installing it (under floorboards) I tested it against more expensive optical and coax leads which I borrowed. I was using a Sony ES player, a couple of different DACs and a grands worth of Stax headphones. There was absolutely no difference in sound quality.

    I remember reading about an experiment someone had done using the shattered plastic of a biro to connect the output of a transport to the input of a DAC and there was no subjective or measurable difference between that and a fancy cable.

    I don't understand any of the science but I have to admit it does sound reasonable that with digital it's either there or it isn't. Isn't it just like reading data from a disc on your PC?
     

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