Your Digital Media Has Never Looked So Good

 
pg_rider
Topic Author
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Anyone heard of/tried a "digital" subwoofer cable?

Tue Jun 28, 2005 2:51 pm

Went to Frys to get a digital coax (SPDIF) cable to hook up my HD1000 and the cheapest I saw in the length I need was $40. Sitting right next to it though was a cable made by RCA marked as a "digital subwoofer cable" for $15. Looks just like the SPDIF, and the drawing and specs on the back of the package are all similar to the SPDIF. Anyone ever heard of such a thing, or tried one and had any luck? Can't try it til I get home, but wanted to see if I should even bother opening the package or if I should return it for a true SPDIF cable...
 
rem
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Location: southern cal, usa

Tue Jul 05, 2005 10:37 pm

i don't know the technical details, but all digital coax cables are basically standard rca cables. it's just that the something or other (the term escapes me at the moment...maybe impedence?) is different.

and a standard rca cable will deliver your digital audio signal. i think the difference is that it's more prone to interference than a "genuine" digital coax cable. since it's a digital signal, it will either give you sound, or it won't. there's no in between. in the case where there's interference, you will notice a complete drop-out of sound, not one that is staticy as in an analog signal.

as for a subwoofer signal, i did not know that it can be digital. i thought all amps/receivers that have a separate sub-out actually deliver an analog signal.
rem
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pg_rider
Topic Author
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Location: Colorado Springs, CO

Wed Jul 06, 2005 8:58 am

Thanks for the reply. That's pretty much the same feedback that I got from avsforum.com. I ended up not even trying it; just brought it back to Fry's and got a "real" digital coax cable. Works like a charm! Although I'm tempted to plug in a standard RCA cable to see if it works... :wink:
 
rem
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Wed Jul 06, 2005 8:54 pm

i've tried. it works. i just use a high grade single composite cable such as that from monster cable. but anything well-shielded works well.

luckily, i'm not such an audiopile to be able to tell the difference. try it for yourself. if you don't hear any difference, return the more expensive cable. you've nothing to lose.
rem

roku digital video player wireless

m500 hard-wired (2)

m1000 hard-wired (1)

firefly mediaserver on winxp

firefly mediaserver on mss+

d-link dgl-4300 router

(static ip on everything...except the netflix player)
 
flar
Posts: 40
Joined: Thu Jan 06, 2005 4:17 am

Thu Jul 07, 2005 2:08 pm

A couple of things.

Digital sound isn't completely "you hear it or you don't". The wire is an analog transmission medium so the 1's and 0's are being deduced by the receiving side based upon the voltage signals coming through the wire which are themselves analog in nature.

So, while the interference that may come from unshielded cables may not be directly audible to you, that interference is audible to the receiving circuitry that is trying hard to "listen" for the 1's and 0's.

Luckily the standard includes some error correction allowances, but as your interference on your digital cables increases, the degree to which you allow on the error correction increases. Some error correction is purely mathematical and can be corrected with certainty due to the redundancy in the data, but sometimes the circuitry uses a simple filter to guess what the missing data was when the redundancy fails for a few samples.

So, in reality the failure mode is along the spectrum of:

- Perfect reception of the original data
- Error corrected reproduction of the original data
- Filtered approximation of the original data
- Unable to see enough data to even approximate a sound waveform

Unfortunately, most home audio electronic gadgets lack any feature to show a statistic on how often they are invoking error correction. Most motorola digital cable boxes have a utility menu that lets you see the counts of errors and how many could be corrected in real time so you can futz with the type of coax cable you use to connect to the cable socket. Doing so shows that good strong generic cable which can be bought for a very reasonable price is just as good as a commodity voodoo cable and both are better than cheaply made mass-produced cheap-looking cables.

All coax cable is damaged by extreme bending which causes the non-conducting materials in the core to crease and no longer keep the desired separation between the signal wire in the middle and the sheilding on the outside. If you roll it around something it shouldn't be a problem, but if the radius get small enough that you see it starting to crease, then you are violating its spec for how close the signal and shield conductors should get.

Thin coax can be as good as the thick stuff until the first time you try to bend it around a corner and then the extremely tiny core refuses to bend back into the right shape again and it is forever reducing signals. If you need to use that kind of cable, be very careful with bending it.
 
PRMan
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Sun Jul 10, 2005 7:28 am

I just use a very thick, well-made RCA yellow video cable. Sounds perfect to me.

You would want to avoid cheap, thin stereo cables, but anything that's thick enough to handle the bandwidth and looks well-made should be fine.

Monster has made more money off lies than any other company around.
PRMan
 
dgburns
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Mon Jul 11, 2005 10:18 pm

PRMan wrote:
I just use a very thick, well-made RCA yellow video cable. Sounds perfect to me.


Ditto...

PRMan wrote:
You would want to avoid cheap, thin stereo cables, but anything that's thick enough to handle the bandwidth and looks well-made should be fine.


Agreed. There's a difference between a cable you'd run between a coaxial digital audio output from a DVD player (or a Roku...teehee) and the cable you'd run between amp and subwoofer. Must be a VERY esoteric amp to have a digital output to a subwoofer. I've personnally never seen such a thing, nor a sub that had digital audio input, but heck they COULD be out there...

PRMan wrote:
Monster has made more money off lies than any other company around.


I've bought Monster stuff, I've bought Radio Shack stuff. I >DO< find the Monster stuff more reliable long term, less tendency to get brittle etc., but I've personally not wanted to spend the time to do double blind qualitative comparisons. I don't think Monster >LIES<, but their marketing is definately full of FUD to the point of making the average consumer THINK if they don't use Monster's products they'll have poor picture and sound, which is just not true.
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flar
Posts: 40
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Mon Jul 11, 2005 11:22 pm

PRMan wrote:
I just use a very thick, well-made RCA yellow video cable. Sounds perfect to me.
What matters most here is that you use a coaxial cable for these digital signals as these circuits are expecting a specific impedance. Video and digital applications both require 75 Ohm impedance, analog applications do not. If it is spec'd at 75 Ohms and it feels good, then it probably is fine. If it was sold as an audio cable, then you have no guarantee on its impedance. The "yellow video cables" bundled with most A/V equipment should be 75 Ohm, but may not be of decent quality construction. http://www.epanorama.net/documents/wiring/cable_impedance.html talks a little more about how cable impedance is measured and forum discussions such as http://www.avsforum.com/avs-vb/showthread.php?t=426382 deal with whether or not cheap cables meet the specs and whether or not they are "good enough". The way I view them - in pristine condition they probably meet the spec, but their durability may be questionable.

You would want to avoid cheap, thin stereo cables, but anything that's thick enough to handle the bandwidth and looks well-made should be fine.
You probably do want to avoid cheaply made cables, but their thickness is not really a good indicator. As long as they are specified at 75 Ohms then the thickness of the cable will be appropriate for the dielectric used to separate the inner and outer conductors. The thin coax cables you see, which are mostly from the boutique cable brands since they market to the "style conscious", are simply using a different dielectric to allow a smaller distance between the inner and outer conductors. The main issue with the quality of a coaxial cable is how well it maintains the distance between the conductors when you bend it. If it creases then the two conductors will be closer where the crease is and the original impedance spec is no longer accurate. If a given cable bends well without creasing or resists bending in the first place (again without creasing), then it will likely maintain its specified impedance well since it will maintain the distance between the conductors reliably as you handle it and install it.

Monster has made more money off lies than any other company around.
More like false promises - that their cables have a property (which they probably do) that matters to the intended application. On the other hand, some of the moderately priced boutique vendors do produce cables with some desireable properties - like they may bend more easily without creasing which would make them more useful in using in a tight space. A cheap brand X cable will likely be fairly stiff and will be ruined if you try to bend it too much - not a problem if you have plenty of room to install it in with few corners to navigate.
 
PRMan
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Thu Jul 14, 2005 7:33 am

I was referring to their claim that their fiber optic TOSlink audio cable will give "richer, warmer sounds" than brand X. Right. Sure. That's when I stopped considering them altogether and bought a cheaper one from RCA. $11 vs. $44. Even if it breaks or goes bad, I could buy 4 RCAs.

Looking at their website, I see they no longer advertise them that way. They now correctly mention jitter as the primary problem.
PRMan
 
flar
Posts: 40
Joined: Thu Jan 06, 2005 4:17 am

foo

Thu Jul 14, 2005 12:05 pm

Actually they still have some of that on their web site. If you go to the page for the "Interlink Lightspeed Reference Fiber Optic Digital Cable" it still says:
    greatly reduces jitter for enhanced clarity and definition
    Graded index optical fiber for smoother, more natural sound

I don't know, I guess that jitter would reduce clarity and definition, but I'm not sure how the index affects the "smoothness" of the sound. It probably affects something, but with a digital signal, the receiver is probably the entity that most enjoys these effects "Aaaaah - these 1's and 0's sound/look so nice!"

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