RCA vs Coax Cable
December 25, 2004 4:06 PM   Subscribe

Stereo/home theater cable question(s): Can you use a "regular" RCA cable as a "Coaxial digital" interconnect for digital audio from, say, a DVD player to a receiver? The plug seems the same size, but don't know if it carries the same signal. Similar question: can you use a standard AUDIO RCA cable (red or white) to carry a standard VIDEO RCA signal? Or does it have to be the yellow-labeled RCA?
posted by robbie01 to Technology (26 answers total)
I dunno the answer to your first question, but yes, you can use one of the red or white ones in the place of a "yellow" RCA cable. They're all the same inside, just make sure you connect things up the same way on both ends.

I gather you're doing some post-Christmas cable scrounging for some fun new goodies?
posted by bcwinters at 4:21 PM on December 25, 2004

BCWinters is right. The color coding is simply to avoid confusion when hooking things up. The cable itself is the same.
posted by Bugbread at 4:28 PM on December 25, 2004

And yes, the same cable will carry your digital audio.
posted by Duncan at 4:34 PM on December 25, 2004

It's all exactly the same metal inside.
posted by Keyser Soze at 4:46 PM on December 25, 2004

While it *might* all be the same metal inside, there are potential differences in resistance, and more importantly, shielding.

Unbalanced audio over RCA is normally below 22kHz, and at low power levels, so shielding is less critical from the leakage perspective, but more critical from the contamination side.

(Composite NTSC) Video is below 3.58MHz, and because of the high frequencies involved, the shielding is usually better than audio cables.

Digital Coax specifically has to be 75 Ohm, and should be well shielded.

Video RCA cables are usually 75 Ohm, so you could probably use that, but if the shielding is not good, some of the signal might leak out and manifest itself in other components.

So, that Yellow wire is your best bet, but at the very least, if you aren't going to get a cable rated specifically for digital audio, get a 75 ohm video cable which you know has both a braided shield and a mylar shield.
posted by tomierna at 5:46 PM on December 25, 2004

Standard audio cables are nothing like long enough for impedance to matter, and you only need to worry about shielding if you see problems. Digital audio signals are robust enough to survive whatever distortion a cheap cable introduces, as is composite video.

In short, yes.
posted by cillit bang at 6:19 PM on December 25, 2004

Thanks guys, and yes, setting up some new audio eq. for the girlfriend and she's a little low on $80 digital Monster audio cables, and the only thing open around here on Christmas Day is Rite-Aide -- slim pickin's for high end audio interconnects.
posted by robbie01 at 8:01 PM on December 25, 2004

You know, the "Monster" digital coax cable always struck me as one of the bigger rip offs in hi-fi.

Now, I come from a software background, not an EE, but it seems to me that if its "digital" it, well digital. Its like a network cable transmitting some bitstream of the sound at a certain bitrate. Now, I know nothing of the protocol used by digital coax, but unless it has some sort of underrun protection aka streaming audio codecs, you are either getting the bits, or your not (and would hear clipping or stuttering)

Its not analog. As long as the DAC can distinguish between a 0 and 1 on the line, who cares how noisy it is. Your never going to get a 'better quality' 1.

I mean, its freaking binary folks.
posted by PissOnYourParade at 11:37 PM on December 25, 2004

(fyi / in response to cillit bang's comments, which i think mention impedance in response to the 75 ohm numbers) when people talk about "impedance" of cables at high (radio) frequencies, they're not talking about ohmic losses, but whether or not the cable will match the electronics correctly. using the wrong impedance cable will reflect energy at the plug, making it less likely to work (and in very strange circumstances perhaps damaging the source, though i doubt that normally).
posted by andrew cooke at 3:44 AM on December 26, 2004

Not to politicize the thread, but you should probably avoid Monster cable, as it is one of the Evil Companies. Google "Monster Cable lawsuits" for more, but they're basically suing everyone with the word "Monster" in their name, such as Monsters Inc., Halloween costume companies, and the Chicago Bears for having the nickname "Monsters of the Midway". Plus, their cables are way, way overpriced for what they offer.
posted by Bugbread at 3:56 AM on December 26, 2004

I hate to do this as well, but it should speak for how strongly this geek feels about it, as I've been pretty well behaved here in the green. Don't buy Monster brand cables. They sell very expensive snake oil. Also, I'm almost afraid to say that here 'cause I don't want MeFi/Matt or myself to get depantsed via lawsuit.

To actually contribute, I'm currently running two video devices on audio branded RCA cables, and they're cheap-ass ones. Looks just fine, no problems or noise or anything on either the DVD player or N64. It might be slowly breaking the connected devices, but I doubt it. Most consumer grade stuff these days has been engineered to be munge-proof. The engineers plan for people plugging the cables in the wrong way and stuff.

And what tomierna, POYP, and andrew cooke said.
posted by loquacious at 4:26 AM on December 26, 2004

Andrew: reflection only occurs when cable length (in m) * frequency (in MHz) > 30, which allows 6m for a 5 MHz composite video signal.

PissOnYourParade: Real-time connections have no re-transmit facility, so therefore the receiver often has to make up data to mask lost packets. Therefore higher quality cables => Less packet loss => Less making up data => improved fidelity.
posted by cillit bang at 4:38 AM on December 26, 2004

ok (the pedantic physicist in me wants to say it's really not that simple, but if that's a standard rule of thumb then it's probably more useful than any long error-filled and over-theoretical calculation of mine...).
posted by andrew cooke at 4:43 AM on December 26, 2004

do you have any numbers for the cable quality argument? i would have thought that (1) there's a relatively small region between useless and inaudibly close to perfect, outside this cable choice will make no difference, and that (2) it's not clear to most consumers what's cosmetic and what's actually relevant to good signal path (so you may pay a lot for cables that look fancy, but which preform equally to cheaper ones).
posted by andrew cooke at 4:52 AM on December 26, 2004

The rule of thumb is that transmission line effects only occur when the cable is more than 1/10 the signal wavelength, and a quick google calculation gives me the number thirty.

Re: error rate. Yes. The only numbers I have concern minidisc read errors, the relevant part being that with most errors the correct data can still be calculated, meaning zero audio distortion. I imagine, except in very noisy environments, the actual amount of packet loss is rather small. But that's the audiophile argument for expensive digital cables (I use very cheap but fancy looking ones, which your mall electronics store will resell for 900% markup).
posted by cillit bang at 5:55 AM on December 26, 2004

if you are feeling vaguely handy, it's fairly easy to make your own high quality interconnects, and relatively cheaply.

belden makes a nice coax (89259; 89207 also good) with foamed teflon insulation and teflon jacket, and canare (switchcraft, cardas, kimber, etc.) rca plugs are not too expensive, and then it's just a question of a few tools (stripper, crimper, maybe soldering gun) and some heatshrink tubing.

I've been using such a thing for digital interconnects for the last ~4 years and it sounds superb.
posted by dorian at 8:48 AM on December 26, 2004

Myself, I choose my RCA cables based on the quality of the RCA plug. I haven't the foggiest idea what I'm using for my subwoofer and digital audio cables, but I do know that the RCA jacks are gold-plated, spiral-cut, fit really tightly, and are well-secured to the cable. The back of the box probably described the wire as oxygen-free, high-grade copper with full shielding, which would be pretty much standard issue for a decent RCA cable. Given that the two components to the cable seem to be reasonably good quality, I feel I can safely assume it's every bit as good as any of the ultra-priced snake oil.
posted by five fresh fish at 10:36 AM on December 26, 2004

Along the same discussion, though, I ask this:

Bananna plugs or use the screw-downs on the posts?
posted by five fresh fish at 10:37 AM on December 26, 2004

cillit bang - thanks for the info.
posted by andrew cooke at 11:03 AM on December 26, 2004

Banana plugs are easier to deal with. Use them.

If you think you hear a difference, arrange for a friend to help you do a double-blind test. If your receiver has 2 sets of speaker outputs, have him/her hook up a banana plug to one set and bare wire screw-down to the same speaker of the other so you don't know which is which, and see if you (and maybe one or two other people) can hear a difference for real.

Even better, have him/her do the switching at random while your back is turned, and you call out whether it's the banana plug or the bare wire (or even the A or B).
posted by ROU_Xenophobe at 11:06 AM on December 26, 2004

Monster cables! ARGH!

Here's the secret: STOP USING RIP OFF CABLES. :-D

Buy one box of 1000 feet of cheap RG-6 satellite TV cable. It will cost you about $50. Now you cut it to size. Go to your surplus shop and buy F -> whatever-you-use connectors (usually F -> chinch/RCA/phono connectors). Virtually everything you own that requires impedance matching is going to be about 75 ohms, unless you're into HAM radio or have a 10base2 or arcnet network, so RG-6 is awesome.

Now your cables will cost you about $1 - $2 each and be better quality than monster cable.

BTW: The digital signal will run through almost ANYTHING. I used zip cord (20 feet) without trouble once.

Oh, gold vs. chrome vs. no plating? If you look up the resistances, no plating is better. But at least with gold and chrome plating your connection won't tarnish. So, go with chrome plating. Cheap and functional.

For audio quality, there's no way in hell you are going to hear any audible difference between almost ANY connectors and any "distortion" they introduce. At 20 KHz the signal frequency is just too low to be affected by any capacitance/inductance/resistance in the wire.

Anyone who disbelieves me is welcome to look at the comparison on my oscilloscope.
posted by shepd at 11:10 AM on December 26, 2004

Pah. Everyone knows that it's the tiki-tiki wood counterweights placed at the reciprocal reflection points that will cause your digital bits to lose that sharp quality, resulting in a more mellow and, frankly, melodious sound. And at only $300 per weight, it's a relative bargain. In fact, I carefully placed one on my AC line filter, thinking that it might work to remove the frequency fluctuations, and I swear that my bass is much roomier and that my trebles are more focused!
posted by five fresh fish at 4:42 PM on December 26, 2004

Tiki-tiki wood? Gee-zus, why not use tin cans and string?

Personally, I find that speaker stands made from the femurs of saints, carved with some inscriptions the Fabricator once read in R'lyeh and topped with mounting-brackets made from the severed hands of criminals really opens up the soundstage. It actually transports me to another place and brings to mind the most wonderful visions...

The only problem I have now is that the hands are from such common criminals... a friend has mounts made from Dahmer, and I have to admit that his sound has a certain squalous fecundity that mine lacks. And they keep cracking their knuckles before the music starts, which can be a little bit unsettling.

I just wish I knew why I'm only supposed to listen inside the circle. Seems to me the sweet spot should be just outside, right where it says "ftaghn" in the tilework... then I'd really be able to hear what New Kids really ought to sound like.
posted by ROU_Xenophobe at 8:46 PM on December 26, 2004

The last two comments are hilarious and informative, as they illustrate the lengths that hard-core audiophiles will go to to achieve better sound.

There's all kinds of weird stuff out there. Pens with "magic ink" that is applied directly to CDs that somehow expands dynamic range and reduces the "harshness" of digital audio. Weird speaker mounts. Cables blessed with sacrificial goat blood.

Some of it actually works, like speaker enclosures crafted from fine woods, tuned and ported like a musical instrument. And speaker stands that reduce unwanted vibration and increase bass transfer to the floor.

Speaking of audio, I'm now the proud owner of a brand new 60 watt 2.1 desktop system. I have a subwoofer!! YAY! Now I just need to tune it and figure out where I'm placing my speakers and stuff. And maybe integrate it with my old two-way self-powered desktop monitors that offered decent clarity and mid-range.

I really wish that I could still find an inexpensive set of self-powered two or three-way desktop speakers instead of all this tinny subwoofer-plus-satellites crap they're peddling these days. Great. I've got bass response in buckets of mono hell and two tinny, shrieking little tweeterpods that have all the midrange response of a piece of buttered toast strapped to a cat. (Though, I'm hoping my new system will change my mind about that. The satellite's are actually two-ways, with a mid range driver and real tweeter domes and everything.)

Also: Fuck Bose, Harmon Kardon, JBL and Klipsch. For selling out and/or selling import crap merely branded with their badges. Bastards. You'll get yours when the revolution comes. *goes back to building 100 megawatt servo-driven mass-driver bass cannon capable of exploding heads and melting concrete.*
posted by loquacious at 11:40 AM on December 27, 2004

Loquacious, you need this!
posted by five fresh fish at 12:31 PM on December 27, 2004

I would actually love to hear that rig, Mr. Fish. Looks cool. It also looks a bit cluttered and possibly vibration-prone.
posted by loquacious at 12:56 PM on December 28, 2004

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