Why not to waste money on expensive digital cables

Discussion in 'General Hardware' started by Aprox, Apr 12, 2007.

  1. Aprox

    Aprox Moderator Political User

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    I figured I would post this so people would understand why you should not waste lots of money on expensive name brand digital cables. (DVI, HDMI, Toslink Fiber, Coaxial Digital, etc)

    Link

     
  2. zeke_mo

    zeke_mo (value not set) Staff Member Political User Folding Team

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    Lol, same reason I make my own cat5e cables, the "fancy" ones are nothing more but a pretty version of my homemade ones, and they cost more :p
     
  3. epk

    epk Moderator Political User Folding Team

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    that was pretty obvious... i still prefer branded ones, because cheap ones break too easily
     
  4. zeke_mo

    zeke_mo (value not set) Staff Member Political User Folding Team

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    Do you use them for a jump rope? I've never had a cheap cable break on me before.
     
  5. Aprox

    Aprox Moderator Political User

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    It may be obvious to you and others, but I just posted this to help out who dont know this kind of stuff. You can easily be ripped off by sales people at your local retailer or just by getting bad info online and ordering something that is way overpriced.

    How do you break cables? Do you pull on them and stuff? I could see investing in nice cables if you hosted events or setup large amounts of cables all the time and they got moved around a lot but for most consumers the cables are going to be plugged in and forgotten about then collect dust.
     
  6. zeke_mo

    zeke_mo (value not set) Staff Member Political User Folding Team

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    When my sister used to work retail she would scan item with some magical scanner thing and it would tell her the mark up on inventory. I had her scan some USB cables for me and the markup was 98%...
     
    Last edited: Apr 13, 2007
  7. epk

    epk Moderator Political User Folding Team

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    the plugs break often when unpluggin

    maybe cheap cables in the us are the premium ones here in argentina, idk ;)
     
  8. trainmaster77

    trainmaster77 Moderator Political User Folding Team

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    yes ..this is an excellent post. The only thing gained with "higher quality" cables is distance ... and higher quality meaning ...thicker ofc copper. Shielding is a given ..i don't know of any cables that aren't ...

    so ..next time you are at best buy and the salesman leads you to those 100+ monster cables ..tell him to shove it.
     
  9. Grandmaster

    Grandmaster Electronica Addict Political User Folding Team

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    Basically the only reason sales people get you to buy those $200 power cables is because they make the most commission off of accessories.
     
  10. zeke_mo

    zeke_mo (value not set) Staff Member Political User Folding Team

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    Something looks different...your avatar isnt as sexy as it used to be..
     
  11. ray_gillespie

    ray_gillespie Moderator Staff Member Political User

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    I remember my brother had a PC from Dell which came with a free colour printer - it didn't come with the USB cable though, and Dell wanted £15 for one! Easy to see how they can afford to give things away for 'free' when people are conned into buying stuff like that.

    I bought him one for £1.99 from a market :)
     
  12. epk

    epk Moderator Political User Folding Team

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    definitely cheap cables in the us are not the same as the ones in argentina... not even all branded ones here have decent shielding
     
  13. LeeJend

    LeeJend Moderator

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    Wow - is that guy a crappy engineer. He understands nothing about digital transmission over transmission lines. Ignore his post.

    What differentiates a good cable from a bad cable has nothing to do with cost. There are good cheap cables and bad expensive cables.

    Bad cables:
    -Have higher intrinisic parasitic capacitance which further distorts the square waves.
    -May have conductor diameter, insulation thickness variations and kinks in the cable caused by poor quality control that create signal reflections further degrading the square wave.
    -There are multiple grades of cable shielding to prevent external noise from affecting signal quality, stranded, bel-foil, etc. The amount of shielding varies from 80% to 99%.
    -Unplated connectors that will develop oxide over time reducing current and degrading voltage waveforms. Good connectors have self wiping terminals on them that wipe off the oxide when they are mated and de-mated.
    -Cheap manufacturing, i.e. poor quality control and worn out equipment can result in connectors not tying to the shields properly.
    -My two favorites from careless assembly:
    --The fake wire. I have repeatedly found wires where the conductor is broken or cut in the middle of the strand but reads good for a while until the cable gets moved around a few times then opens up.
    --A pin crimped onto a wire where the insulation was not stripped off to the proper length. These also work for a while then suddenly stop working as the insulation flows under the crimp and opens the connection
    My credentials - 36 years doing high speed data signalling on planes trains, automobiles, ships, gournd based computers and bio-med equipment.

    This is a little more accuarte:
    http://www.digido.com/modules.php?name=News&file=article&sid=15
    http://piers.mit.edu/piersonline/pdf/Vol3No2Page215to219.pdf

    Google "digital waveform distortion" for hundreds more explanations of why the guy in the quoted post needs to attend an acredited university before calling himself an engineer. It's all covered in Electromagentic Effects 101 and Pulse and Digital Engineering 101.

    Damn I hate amatuers calling themselves engineers!
     
  14. ming

    ming OSNN Advanced

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    Can you define the difference between a Digital Cable and an Analogue Cable? From what I see, they both contain copper wires which are prone to interference from EMI.

    I seen a BIG difference in quality of picture between a cheap EuroAV cable (SCART) and an expensive cable which are shielded, and in the case of SCART cables, the more expensive cables do not have missing wires.
     
  15. trainmaster77

    trainmaster77 Moderator Political User Folding Team

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    analog cable is just that ... standard rca types ...which have basically negative and positive polarity ....

    digital cables such as scart, HDMI, DVI ..ect somehow encrypt the data before passing it from one end of the cable to the other.

    I think in reality ..they could make the rca type calbes digital ...but they don't.
     
  16. Tuffgong4

    Tuffgong4 The Donger Need Food!!!! Political User

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  17. Steevo

    Steevo Spammer representing. Political User Folding Team

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    DVI and fiber optic.


    I still see no reason for HDMI other than to increase the grip on DRM protected media, and frankly I find it absurd.


    Yes, with Toslink I have found no conclusive evidence that it will carry 7.1 32 bit music. But really, it is not the depth of music that needs the increase, but the precision. But what is in place to really take advantage of it?
     
  18. LeeJend

    LeeJend Moderator

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    Yes, all cables are copper and a dielectirc (insulator).

    A 1 mhz analog signal requires a cable with an ~1 mhz bandwidth to carry a sinewave. Amplitue or frequency modulate it to carry data and the bandwitch needs to be 1 mhz +/- 100 khz. A small range easy to control.

    A 1 mhz digital signal can actually be decomposed into a collection of analog sinewaves comprised of harmonics from 1 mhz up to 50 mhz (above 30-50th harmonic they are pretty much negligible) using Fourier analysis. That means a digital cable has to have 50 times the bandwidth of an analog cable to get the signal through still looking like 1's and 0's.

    So why use digital?
    -Error correction can be applied to digital signals using parity or checksums. Message failed? Send it again. Analog can't do this
    -Digital signals can carry more data than analog in the same bandwidth through compression and becasue the digital does not have to be encoded onto an analog carrier like analog does.
    -Accuracy! If an error corrected red dot make its to your screen that red dot is the exact position, color and intensity that was intended. An analog red dot can be the wrong intensity, phase shifted (ghosting) and the wrong shade of red. Analog can correct for some of this but not much.

    The difference in "digital cables":
    -the high frequency impedance of the copper (fine threaded is better but harder to work with than larger strands).
    -how much of the high harmonics the insulation absorbs. This is controlled by the basic material plus if the material absorbs atmospheric moisture.
    -Thickness of the wire insulation the dielectric constant of the insulating material affects the caapcitance of the cable which controls attenuation of harmonics and combines with the inductance to effect reflections and the characteristic impedance of the cable which must be matched to the transmitter and receiver.
    -the number of twists per inch of the various strands around each other and how those twists are interwoven determines the cable inductance which controls reflections and signal attentuation. Twisst per inch also determines resistance to magnetic fields (like around a lound speakers, motors, power supplies).
    -shielding can be of various types from twisted, to braided to "bel-foil", to solid. How much external electrical field noise is rejected varies from about 70% to just <100% (nothing is perfect).

    And ya'll just thought a cable was just copper and rubber? Shame, shame. Guys spend 10 years in University and most of their lives figuring out how to get you that 3 Mbps DSL and crystal clear voice to your house over the crappy old phone wires for just $24.95/ month.
     
  19. Aprox

    Aprox Moderator Political User

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    While I cant question your knowledge since I'm not a engineer, I do understand the basic principles of what you are saying. I took -basic- electronics courses in Highschool, so I understand some of what you are saying. That being said, perhaps the engineer that posted that information is not the most educated, I don't know. However I still think the premise of his post is still valid. Do you think average people, or anyone for that matter would be able to see see the difference between a 10 - 30$ cable and a 100 - 200$ digital cable? Sure on paper there might be differences, but do those differences translate into obvious tangible artifacts, distortions or other issues? Thats the real point, as the engineer states in his post in layman's terms digital signals are far less likely to be corrupted than analog signals. So in a consumer A/V world, as long as the signal gets to where it needs to be then thats all that really matters?
     
  20. ming

    ming OSNN Advanced

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    As I mentioned... You actually can see a difference in quality between cheap and expensive cables. However, I've only seen Scart cable comparisons because they have 21 pin connections. I've cut a cheap cable and a Monster cable and first thing I saw was difference in number of cables inside. Although Scart is 21-pin, the cheap cable had missing wires and had no insulation around the wires, while the Monster cable had extra wires connecting all 21-pins and had insulation around the wires.
    With the expensive cables, you get a much richer picture quality than the cheaper ones.