Audible signs of electrical noise in cables?

Hi, guys. I would like to know what are some of the audible signs of electrical interference in analogue interconnects and digital coaxial (and speaker wire, I guess). Sometimes I connect a DVD player to my receiver with a video cable as an improvised digital coax and, if I'm not careful, the cable touches the power cord. Sometimes the sound is harsh, but I don't know if it is the actual CD or DVD that sounds like that.

Thanks beforehand...

 

If your speaking about an RCA coax typically colored yellow I believe those are virtually identical to an audio digital coax both with 75 ohm. In fact some companies, or at least Kimber, identify theirs as audio/video digital coax.

I think one consideration in the quality of the cable being used and potential interference is whether or not they are shielded. If the cable is older and of cheaper construction there is a possibility that the shielding could be damaged.

One recommendation I've read many times is when interconnects and speaker cables must cross power cables try to have them at right angles to the power cable and not parallel.

Finally, the issue of sound quality between cables. I Spent fair amounts on cables over the years. I've always wanted better cables for the quality of their construction. My experience is I have heard differences in analog interconnects, speaker cables and power cables. When it comes to digital interconnects of all types I've struggled to hear differences given that each cable was in good working order.

 

It's not the yellow RCA, but the green one from a component video cable (Radioshack). They're the same. The cable is shielded (supposedly). And it's not old.

Thanks. At right-angle? Interesting. Will try it. The RCA cable goes out vertical down to the receiver and the power cord crosses it to the left.

 

That is not a digital cable. That is an analog component video cable. I would not use that for digital audio connections. I remember my brother doing that years ago and I noticed the sound was wrong. Switching to a yellow digital cable solved the issue.

 

Video Only Analog Video Graphics Array (VGA) D-subminiature 15 pin
Composite. Often designated by the CVBS acronym, meaning "Color, Video, Blank and Sync". RCA jack, normally yellow (often accompanied with red and white for right and left audio channels respectively)
S-Video aka Separate Video. Carries standard definition video and does not carry audio on the same cable. Mini-DIN 4 Pin
Component. In popular use, it refers to a type of analog video information that is transmitted or stored as three separate signals. Either RGB Interfaces or YPbPr 3 RCA Jacks

 

Ok. Too bad, I thought the three RCAs from a component set were just like three yellow composite video RCAs.

 

Sorry but no. That's why your hearing a degradation in the sound. Oh and be sure it is a digital cable. If I remember correctly the analog cables (composite) used prior to component were also yellow.

 

mwheelerk, I read this thread before using the component video as a digital coax:

http://forums.stevehoffman.tv/threads/can-i-use-component-video-cables-for-audio.312848/

 

I read just the first couple of posts. They are talking about an analog connection between the amp and preamp unless it deals with digital connections later in the thread but the OP point is analog.

 

They are the same. He is mistaken. A component video set should be just 3 of the same 75ohm coax bundled together, which are appropriate to use for analog video or digital audio (or 75-ohm digital video) applications.

 

Physical touching or not is not the issue, but rather proximity, and parallel proximity over long distances. That being said, 60hz noise into a digital signal should not batter at all, and it is unlikely that it would impact the reception of the digital signal enough to cause signal failure. If you are hearing sound, it's not a problem.

 

Those are the same thing. A 75 ohm coax is a 75 ohm coax. That is the appropriate type of cabling to use for a digital audio or analog video application.

 

I'll respectfully disagree. The analog component video cables to what I understand and read are not the same as a digital coax spdif cable although they both have RCA connections

 

Video cable carries RF so it's essentially the same as coax SPDIF cable.

It's extremely unlikely a nearby power line will cause a problem with a digital signal. I'd be willing to bet that if it did interfere with a digital signal it would cause unmistakable dropouts, not some vague "harshness".

Frankly it's a grossly overstated risk even for analog connections. If a power line did interfere with analog it would not make it sound "harsh", it would simply inject some 60Hz. As a professional sound engineer I've run extension cords next to an audio cable bundle ("snake") for 75 feet many times with no audible effect. Running audio and power together is routine in pro sound.

 

I think I will correct myself, apologize and step aside. I have read further, not really visiting this subject in several years, and believe I have confused the issue.

 

I will only slightly disagree with you, but only in the consumer environment. In pro-sound, I wholeheartedly agree, largely not a concern, but this is because you're generally dealing with balanced lines (over XLR cables). They will (or should) reject noise like 60hz hum, and so it's less of a concern running them, even long distances, along with power lines.

However, in the consumer environment, you're usually dealing with unbalanced lines, and they cannot reject noise, they can only attempt to shield from noise. But low frequency noise like 60hz from power lines will go right through a thin shield on an RCA interconnect, and this definitely is a concern if you're running analog cables along power lines, or speaker cabling, or even phone lines.

Professional environments and interfaces are much better at rejecting noise since they are designed around a balanced topology, which consumer devices generally are not, and you're also generally not running dozens or hundreds of feet of cabling in a consumer environment. Going 1 foot along or near a power cable in your equipment rack is not a big deal (though generally you want to route high level & power away from low-level signals when possible as a matter of principle), obviously if you tried to do the same with an unbalanced analog line 50 feet down a snake right next to power cables, you'd have major problems.

ALL THAT being said, you're 100% right that with a DIGITAL signal, even an unbalanced one, still wouldn't be a concern even over very long distances.

 

It's no problem!

75 ohm coax must be used for 75 ohm interfaces, and this is the standard for SPDIF coax digital audio, SDI digital video (in professional environments), and analog video (composite and component). Any quality all-copper 75 ohm coax designed for these applications is interchangeable for any of these interfaces.

A 75 ohm coax is also totally fine to use as an analog audio interconnect.

Exception note: 75ohm coax is also the standard for RF transmission (Cable TV/Satellite), however these signals are of much much higher frequency, and due to the skin effect, travel only on the outside of the center conductor. For cost-saving and resiliance reasons, most Cable TV coax is uses a copper-clad-steel center conductor. A steel-based 75ohm coax is thus NOT appropriate to repurpose for analog audio or any of the digital audio or video applications I mentioned above.

Lastly, unlabeled or obviously non-coax (like twisted pair, woven things like Kimber, strips of silver stuff, other exotic designs) or non-75 ohm coax (like 50 ohm, etc) that might be used or sold as analog audio interconnects (while they may be fine as analog interconnects) are NOT appropriate to use for interfaces that require 75 ohm cabling. So don't use any random unknown or obviously non-75 ohm analog audio cable for a digital or video application.

The short version: Use anything for analog audio you want. Use a 75 ohm coax for anything. But ONLY use 75 ohm coax when required: digital or video applications.

 

We don't really disagree at all, it's just communication style. I took some shortcuts in consideration of the audience.