Cable Question

Discussion in 'Beginners, General Questions' started by Elijah, Aug 11, 2004.

  1. Elijah

    Elijah Supporting Actor

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    Concerning digital cables for audio, am I correct in saying that the type/quality/make/brand for these does nothing at all.

    My knowlege of Digital audio *bitstream* is that the signal is either off or on. That is the nature of digital.

    So in choosing a cable to connect digital audio sources to the reciever there should not be any diffrerence, right?

    It will either work or it wont work.

    If i am correct why doesnt everyone just use a 2 buck mono rca type cable for the digital coaxial connection, or a cheap 5 dollar plastic TOSLink cable?

    I know this is not the case with an analogue signal, as you have to worry about static/signal degredation, however with digital i didnt think that this mattered.

    Let me know if i am missing something fundamental.

    Thanks in advance.
     
  2. SimiA

    SimiA Second Unit

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    You're not missing anything fundamental.
    The less expensive cables will work, but if they're not shielded well, you may experience some RF or EM interferenc; you may not.
    I use them, and at my age, I'm wondering if the expensive cable will produce a noticeable difference in the quality of A/V?!
    I don't buy the inexpensive stuff at Radio Shack, but I don't spend $100 or more on cables either.
    Your eyes and ears will be the best judge.
    There are people who believe, the very expensive cables are the way to go, I'm just not one of them.
    $25-50 is my cut off point.[​IMG]
    Vb
     
  3. Chu Gai

    Chu Gai Lead Actor

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    Concerning digital cables for audio, am I correct in saying that the type/quality/make/brand for these does nothing at all.
    To a point you're entirely correct. I'll simply say there's some merit in having a reasonably robustly made cable that can withstand a modicum of abuse and make a secure connection.

    My knowlege of Digital audio *bitstream* is that the signal is either off or on. That is the nature of digital.
    Close enough for government work but one has to be able to precisely determine what is on and what is off.

    So in choosing a cable to connect digital audio sources to the reciever there should not be any diffrerence, right?
    In terms of consumer products there should be no difference. In fact, I'm of the strong opinion that your odds of having the cable make a difference lies more with high end equipment. However that's not because they're more revealing as there's a fair amount of incompetence when it comes to designing equipment to interface properly. Let me explain just a bit.

    The cable connects two pieces of equipment: the source and the destination. If we look at a coax cable, the source must have what's known as sufficient current drive capacity in order to drive the signal through the cable to the destination. The reason for this is that the cable itself has a capacitance and this capacitance affects what the digital signal looks like. In essesence, a situation with either a ton of capacitance (from a pathologically bad cable design...happens you know but only with esoteric, attractive, pieces of sh*t from reknowned cable designers) and/or poor current capacity will make the edges less sharp. This poorly defined waveform can have problems being correctly interpreted by the destination resulting in small but audible timing problems. For virtually any cable you're likely to buy, the capacitance is somewhere between 15-20 pF/foot. This is nothing.

    As an aside, you might find this link, http://www.hometheaterforum.com/htfo...hreadid=157357 a fun read on the successful use of a coathanger as a digital cable. Its really amazing what you can get away with when the lengths are comparatively short.

    If i am correct why doesnt everyone just use a 2 buck mono rca type cable for the digital coaxial connection, or a cheap 5 dollar plastic TOSLink cable?
    A lot more people do than you think. Just because there's no audible differences does not mean that one always chooses the least expensive approach. A few reasons might be...

    you like to match your cables.
    you like the color.
    you like the connections better (locking RCA's come to mind).
    you prefer a heftier cable.
    you want a cable strictly on theoretical grounds.
    your embarassed to have the word, RCA, Magnavox, Phillips, Radio Shack, whatever on your cables.
    you like your cables to have a certain appearance like techflex.
    you like being able to spend more money than your friend.
    you want better transmission characteristics for your toslink (try glass...I've got a fairly inexpensive source for that).
    you want a toslink that not only you can step on but have Oprah and Rosie Odonnel do the Texas Two Step on (I've got a source for that too).
    you want something no one else has.
    you like hand made.

    Lots of reasons.

    I know this is not the case with an analogue signal, as you have to worry about static/signal degredation, however with digital i didnt think that this mattered.
    Don't be so sure about that. It's easy and inexpensive to get quality there too.

    Let me know if i am missing something fundamental.
    Well you probably can't find that pen you got as a gift last xmas, right?
     
  4. Elijah

    Elijah Supporting Actor

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    Thank you both for your replies to my question.


    Well actually I use it quite often : )

    By reading your replies, i realize that *as with most things that i read on this forum : )*, that there are at least two "Trains of thought" on this subject, and some further research into the topic is going to be needed.

    I recently purchased a couple of peices of equipment to test out and am just using a regular Composite/Stereo Audio triple RCA Type cable spit into its 3 separate cables to function as my Coaxial cable, and i am getting "full" (i know that it is subjective) DD and DTS surround sound.

    So i imagine that i will wind up going with something middle line, or making my own cables, which i like the idea of anyway.

    I am just the kind of person who HAS to fully understand something before i am satisfyed with it. So i wont be able to enjoy my digital audio connection until i know ALL aspects, and viewpoints that surround the topic.

    THis is somewhat painstaking, and usually leads to me being burnt out before i ever get to the conclusion, but that is my blessing, and my curse. This home theater thing is going to be a maddening obsession for years to come as i can see it.

    Thanks again for your answers, i know they were good ones when all they did was bring up more ones : )
     
  5. SimiA

    SimiA Second Unit

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    "when all they did was bring up more ones"
    You're welcome.
    That, after all, is our job! [​IMG] [​IMG]
    Vb
     
  6. Bob McElfresh

    Bob McElfresh Producer

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    Nope. Not that simple.

    You CAN use an audio cable. In most cases, you will get sound and it will appear to work fine.

    But some people have noticed that while watching a movie, the sound will drop-out, every so often. In one case it dropped about once every 15 minutes. In another case, every 2-3 minutes. (One guy was ready to return his brand-new system). The problem went away when a real video or "digital" cable was used instead of the generic RCA cable the people had found lying around.

    So it's important to use the proper "type" of cable.
     
  7. Chu Gai

    Chu Gai Lead Actor

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    And 'tis cheap enough to get a 75 ohm video cable.
     
  8. Elijah

    Elijah Supporting Actor

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    Thank you guys for your responses again.


    That is exactly what I mean when I say "It will either work or it wont work." Not that from the moment you plug it in it will either be on or off for as long as you use it, but that you will know if the cable is working or not eaisly if you have glitches/drops/clicks/beeps in the signal.

    The difference it appears is between "Loss of Quality" (LOQ), and the "Loss of Signal" (LOS).

    With an analog signal you may experience a LOQ, due to a poor cable (bad construction, cable resistance problems...) and not neccisarialy experience a LOS. This would mean that a problem could go unnoticed if it werent that drastic, and you could be experiencing poor audio quality like limited bandwidth, static, unclear highs...

    On the other hand, with a digital signal if you have LOQ again due to a poor cable, you will always experience a LOS, even if momentarialy like you stated with "drop-out's", or pot holes.

    The main point being that with digital unlike analog you will be "easily" able to identify if you are using a sub standard cable (i know it is tougher to identify the problem when it is intermittent).

    All that being said, i use the examples of the cheapest possible cables just as that, examples. I imagine that i will probobally make my own cables, and wind up putting a fair amount of time and effort into thier construcion to ensure they are worth using.

    Again thank you all for pointing out some good points for me to consider, and also some recomendations of what type of cable will best suit.

    On a side note, just out of curiosity have any of you guys made/heard of someone making there own Optical cables?
     
  9. Jeff Gatie

    Jeff Gatie Lead Actor

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    This requires sophisticated equipment to cut, polish, and fuse the fiber-optics. I know guys who have done this, but they had access to the equipment because they worked in the industry.
     
  10. Bob McElfresh

    Bob McElfresh Producer

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    Good for you. Our own Chris White has a good website on how to make cables. It has encouraged many of us to do the same. Likewise, places like BlueJeansCables will whip you up a set of component cables using a similar formula starting at about $50. Stop by the "Tweeks and Connections" fourm for lots of discussion about cables.
     
  11. Andrew-Ghi

    Andrew-Ghi Auditioning

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    Unfortunately, it is that simple!

    Look at the frequency spectrum of any digital signal, and you will soon realize that what might appear as a simple bit stream of ones and zeros, do in reality consist of a number of high frequency components as well.

    In addition, there is also the issue of the quality 'build-up' of the digital interconnect - independent of whether this is metallic or optical.

    While with very short cable runs, there may be hardly any perceptible difference in system performance - always assuming that the end connectors on your cables do provide a good fit - yet this is not the case with longer cables.

    But then what constitute a very short cable run?

    This depends on a number of factors including signal type (audio, high definition video, standard video, digital audio, etc), as well as the signal level. It is one thing running 20 feet of speaker wire as against the same 20 feet for a component-video interconnect.
     
  12. Chu Gai

    Chu Gai Lead Actor

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    Fortunately RG59 is cheap and would be easily up to the task of a 20 foot run.
     
  13. Iver

    Iver Second Unit

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    You need to use the appropriate cable, as specified by the manufacturer of your source device. For an optical connection, use a Toslink cable, price will not affect performance of cable. For coaxial digital use a 75-Ohm RCA-plug-terminated cable. Other impedances of the same type cable will also probably work but there's really no cost difference so you might as well stick with the mfgr's spec. Again, using a cable that fits this spec, spending more will not affect the performance.
     
  14. Leo Kerr

    Leo Kerr Screenwriter

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    A lot of the issues about LOS due to cable issues depends a great deal upon the equipment that the cable is used to connect.

    To my knowledge - it's been a while - my DVD player is connected through a POC audio cable. Panasonic DVD player, Yamaha DSP-A1. Never had a signal issue, either with PCM, DD, or even full bitrate DTS.

    To me, the short of it really is:

    does it work?

    That's the beauty of digital.

    If it doesn't work reliably, then, obviously, it doesn't work.

    The one thing that really tempts me about making my own cables comes from the fact that no where in my system do I have a need for a 1m, 2m, or 3m cable. Virtually all of my connections (save speakers) is
     

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