Drew in the desert Posted July 22, 2004 Share Posted July 22, 2004 Can someone explain to me the difference between audio and video interconnects? For example, I know it is possible to use audio RCA cables to connect the component video conncetions from a DVD player to a TV. Would I be compromising quality if I did so? Are the guts of audio cables the same as video? Quote Link to comment Share on other sites More sharing options...
dougdrake Posted July 22, 2004 Share Posted July 22, 2004 Screw off the barrels on the RCA connectors on both a video and an audio cable and you'll see the difference. Audio is 2 wires (+/-), often twisted, running inside a larger sheath that combines them into a single cable. Video is coaxial, a single wire (axis) running down the center (the +) surrounded by a dielectric, surrounded by a braided shield (second axis, hence "coaxial")which is the - signal and also acts as a shield to keep out interference. Yes, you can use either wire interchangably (heck, you could use coat hangers) but the results may not be to your liking. Quote Link to comment Share on other sites More sharing options...
Malcolm Posted July 22, 2004 Share Posted July 22, 2004 The difference between audio and video cables has to do with the frequencies of the signals they are designed to carry. At video frequencies, transmission line theory comes into play. The impedance of the cable and the devices at each end have to match to prevent reflection of part of the signal back to the source. Reflections cause ghosts and otherwise reduce the quality of the picture. Audio frequencies are not high enough that the cable acts as a transmission line. For short video runs, less than a significant fraction of a wave length, you can get away with using audio cables in place of video cables. You can pretty much always use video cables in place of audio cables. Interestingly, the choice of RCA (phono) connectors was not a good one for consumer video. The characteristic impedance used for consumer video is 75 ohms. Unfortunately, it is impossible with the geometry of the RCA connector and current dielectrics to build a 75 ohm connector. Quote Link to comment Share on other sites More sharing options...
kenratboy Posted July 22, 2004 Share Posted July 22, 2004 I use Radioshack red, white, and yellow connectors for component video, looks fine Quote Link to comment Share on other sites More sharing options...
Marvel Posted July 22, 2004 Share Posted July 22, 2004 Doug, I've hardly ever seen an audio cable with RCAs on it that wasn't coaxial in arrangement. Even on cheap cables. There will be the obvious capacitance issues with audio cables, and the shielding on the cheaper ones is often not very good (some cheaper ones use a spiral wrap as opposed to a braid). Using the RS version of two audio and one video, the standard a/v cable, assures the length of all three is the same, which is one of the critical parts. I'm willing to bet that if you wre to dissect the RS cable, they are all the same (the two audio and one video). I'm not saying more expensive cable isn't out there or doesn't make a difference. You will find the a/v cables with very high quality coax for the video. Marvel Quote Link to comment Share on other sites More sharing options...
dougdrake Posted July 22, 2004 Share Posted July 22, 2004 Marvel - Hmmm, most all audio cables I've opened up have the 2-wire down the middle arrangement. The RS a/v cables are/were nice because they were really 3 coaxial cables, identical in structure, with 2 labelled audio and 1 labelled video. They make great component video/SACD/DVD-A cables. Quote Link to comment Share on other sites More sharing options...
WMcD Posted July 22, 2004 Share Posted July 22, 2004 I think that most of the concerns are overstated. Audio goes from 40 Hz to 15,000 Hz. Video is at about 1,000,000 Hz and above. That established the differences in signal. This would leave one to believe that wire used in audio is not good for video. Not so, at least in short connections like the one, two, or three feet to connect a DVD to a tube. It is true that impedance matching is a concern in very long wires and much higher frequencies. However, if you're moving video a couple of feet, there is no problem. Gil Quote Link to comment Share on other sites More sharing options...
Malcolm Posted July 23, 2004 Share Posted July 23, 2004 Typical audio patch cord is simply shielded, not coaxial cable. Some use coaxial cable, but not the cheap ones. But it typically doesn't buy you anything for audio. On video cables longer than a significant fraction of a wave length, you may not notice a difference between a properly impedance matched setup and one that is not, but the difference can be measured and will translate into real performance differences. You can see it on an oscilloscope and measure it with a time domain reflectometer. This is not an issue if the cable is a couple of feet long. The run is shorter than a significant fraction of a wave length. It is an issue if the run is forty five feet like from my A/V receiver in the hallway closet to the display in the living room. Quote Link to comment Share on other sites More sharing options...
Marvel Posted July 23, 2004 Share Posted July 23, 2004 Malcolm, In a a technical sense, audio cable with a single center conductor, with a shield on the outside, IS coaxial. The center being the hot and the shield being the ground. Far different than Doug mentioning the two conductors being used, usually in a twisted arrangement. The twisted wires aren't the same as twisted pair, per se, as they don't feed into a differential amp as in a balanced line. It's just that one of the two is the hot and one the ground. I can't tell you how many of the cheap RCAs I've cut up to use for different things. Usually to stick a 1/4 inch phone plug on one end so I didn't have to use an adapter. But for most folks, you won't see any difference, even if you could measure it. Marvel Quote Link to comment Share on other sites More sharing options...
Malcolm Posted July 23, 2004 Share Posted July 23, 2004 I am aware that shielded cable is coaxial in the sense that the outer conductor is coaxial with the inner conductor. But it should not be confused with what is called coaxial cable by the manufacturers. That stuff is designed to yield a specific characteristic impedance. FWIW most folks can't tell the difference between Bose and Klipsch, either. Quote Link to comment Share on other sites More sharing options...
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