Using 75ohm cable for analog audio, Good, bad?

Discussion in 'Accessories, Cables, and Remotes' started by Seth=L, Sep 27, 2006.

  1. Seth=L

    Seth=L Screenwriter

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    I have two identical 75ohm cables I want to use to connect my CD player to my integrate amp. Does this have any affect on the sound, good or negative? Is there any difference in the sound at all? Would it be better than using extremely cheap cables?
     
  2. ChristopherDAC

    ChristopherDAC Producer

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    I'm not certain it matters at all. Video cables are always terminated in their characteristic impedance (almost always 75 ohms), which divides the voltage drop equally between the source and sink, wihtout frequency effects, reflections, or the like. This is considered desirable for the high frequencies used in video.

    Audio cables, however, are terminated in high impedance so that the signal appears as a voltage at the output, so the characteristic impedance of the cable is of little interest. I think I read somewhere that they's nominally supposed to be 50 ohm, but I wouldn't depend on that.
     
  3. Seth=L

    Seth=L Screenwriter

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    Thank you for your prompt responce,

    So it is reasonable to assume that if it was cheaper to just manufacter all cables with the same impedance, then they could be manufacturing nothing but 75ohm cables?

    As far as the audio aspect, I didn't think it would make any difference, and so far it sounds fine to me, better than the RCA brand knock-offs I was using.
     
  4. BruceD

    BruceD Screenwriter

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    The fact is today's 75 Ohm RCA cables are labeled A/V because they are designed to work for both analog audio data streams, digital audio data streams, and analog video data streams.

    In other words, your suggested use for a 75 Ohm RCA cable is part of these cable's defined uses.
     
  5. ChrisWiggles

    ChrisWiggles Producer

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    75ohm cable is fine for analog audio. The impedance of the cable is not an issue for analog audio frequencies.

    Impedance is a concern only because an impedance mismatch creates reflections in the wire. These reflections occur at very high frequencies (mhz). Audio frequencies, being mere kilohertz, don't suffer any degradation from this. You can't hear frequencies in the mhz after all!

    But with video signals, where signals are that high in frequency, using a wrong impedance cable cann (and often does) cause reflections in the cable(s) which causes visible ghosting in the image as a delayed reflection of the signal bounces back and forth and reaches the display. Digital audio signals also use signals that are pretty high in frequency and so can also be affected and this can cause dropouts and such.

    So the bottom line is that the impedance does not matter for analog audio cables, but it DOES for analog video or digital connections.

    So, if you have a cable that is 75ohm, it is appropriate for use for any of these purposes. If you have a cable that is not 75ohm, you can use that just fine for analog audio, but you should not use that for video or digital connections at all.

    Hope that explains!
     
  6. Seth=L

    Seth=L Screenwriter

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    I understand completely, thank you.
     
  7. Dennis Nicholls

    Dennis Nicholls Lead Actor

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    A lot of the cheapest audio-only cables aren't coaxial at all...they just use a pair of small gauge wire. At least using coax you may have much improved shielding and noise rejection.
     
  8. Bob McElfresh

    Bob McElfresh Producer

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    Chris - great description. [​IMG]
     

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