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Coaxial Audio: Special Cable? - Page 2

post #31 of 53
5/28/12 at 2:43pm
Quote:
Originally Posted by amirm View Post

Read the papers that I provided. They explain how the interface actually works and how it is not as dumb and simple as it seems.

That's your reply to "Can you tell me which brand and models are"? Your English problem again, amirm.
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post #32 of 53
5/28/12 at 2:47pm
Quote:
Originally Posted by Kilian.ca View Post

A composite video cable (with yellow RCA plug) is also 75Ω and suitable.

Not always. Majority are cheap Foreign & even U.S. made crap.
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post #33 of 53
5/28/12 at 2:50pm
Quote:
Originally Posted by kiwi2 View Post

Might be the problem I'm having at the moment. I have my PC in another room connected to my AVR with SPDIF on an 8 m subwoofer coaxial cable. All fine apart from the occasional dropout. If a light switch is turned on or off or the heater thermostat kicks in, audio playing from my PC across the AVR cuts to total silence for about a second. I never did have that problem when I was using optical for the same thing.

Exactly. It's most likely caused by one of the connectors not properly fastened to the cable conductor or shield. Also check that there isn't a lot of torque being applied to the connection on the PC or AVR chassis. Some strain relief might be needed to keep the weight of the cable from dragging the connection loose. RCA connectors are designed to be cheap, not reliable.
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post #34 of 53
5/28/12 at 8:49pm
Quote:
Originally Posted by diomania View Post

They cause "impedance mismatch and RFI problems"? How did you become aware that it was a problem?

Reading. Try it.
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post #35 of 53
5/28/12 at 9:43pm
Quote:
Originally Posted by domino92024 View Post

Reading. Try it.

Since you seem to be having a hard time understanding my questions, let me expand it for you:

1. How did you discover that the cables came with the equipment was veering off of the standard impedance and have inadequate RFI shielding, did you measure them? If you did, what equipment did you use and how did you hook it up?

2. You called it problems ("prone to impedance mismatch and RFI problems when used as S/PDIF") because you heard the difference? If you did, how did you set up the comparison rig?

3. Let me ask you again with a hope that I will get some info on this, which gear is it that contained such problematic cables in the box?
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post #36 of 53
5/28/12 at 9:50pm
Quote:
Originally Posted by diomania View Post

1. How did you discover that the cables came with the equipment was veering off of the standard impedance and have inadequate RFI shielding, did you measure them?

What equipment comes with S/PDIF cable? You have the make and model?

If you mean audio cable that came with the set, here is a bit of reading: http://en.wikipedia.org/wiki/RCA_connector

"Varying cable quality means that a cheap line-level audio cable might not successfully transfer component video or digital audio signals due to impedance mismatch and poor shielding quality (causing signal-to-noise ratio to be too low). Cables should meet the S/PDIF specification as defined by the international standard IEC 60958-3 for assured performance."

You can find the contributor for that section of Wiki and complain to him...
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post #37 of 53
5/29/12 at 4:31am
Quote:
Originally Posted by domino92024 View Post

Just checked Ebay. Alas, I could find no coaxial/RCA cables for $0.99 including shipping. You must have gotten them all.

I just repeated my search of a few days ago, and it appears that lot of auctions disappeared. Why I this is mystefies me, but I can promise that I purchased none of them.

The good news is that the low water mark is now about $1.49.
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post #38 of 53
5/29/12 at 10:23am
Quote:
Originally Posted by OtherSongs View Post

I kept thinking about the ref by Steve Nugent, where he states: "Typical stock Transports have around 25 nanosecond rise-times."

The article also says that going faster than 25 ns is avoided so that the equipment will pass FCC rules, even when the cheapest coax interconnects are used.

So he assumes 25 ns transport rise-time, and his math works to minimum cable length of 4' 8" (or longer) being preferred.

What is the typical min/max rise-time, for disc transports, in CD/DVD/blu-ray players?

Lessee... for 35 ns rise-time, the worst case would be the same coax cable (roughly 4.5') that'd likely be OK for a "typical" 25 ns rise-time. So 35 ns might need coax length of maybe 7 feet to lessen jitter issues with copper coax cables used for sending S/PDIF digital signal?

I mean, do 10% of current transport units average out at a slower 35 ns rise-time bracket?

Sadly, there is hardly any data on the rise time of signals out of S/PDIF devices. So no one can tell you what it is on any gear you may be using/buying.

The solution then is to shoot this interface in the head and put it out of its misery . I mean, it has been 30 years since it was introduced. At that time, we hooked up printers to our computers using this interface:



We replaced that with USB, why not for digital audio? If we turn the interface into one that produces digital bits at both ends and nothing else, we are golden. That technology is here now courtesy of asynchronous USB. Add electrical/RF isolation to it and you are good to go. Get yourself a music server and a DAC that supports this and you are good to go in my book .
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post #39 of 53
5/29/12 at 11:00am
Copper is copper. As long as both source and destination devices support the interface/signalling, it makes no difference. HDMI or USB or firewire or serial/parallel... etc.

Can't wait for graphs and quotes/references.
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post #40 of 53
5/29/12 at 11:21am
Quote:
Originally Posted by amirm View Post


Quote:
Originally Posted by othersongs View Post

I kept thinking about the ref by Steve Nugent, where he states: "Typical stock Transports have around 25 nanosecond rise-times."

The article also says that going faster than 25 ns is avoided so that the equipment will pass FCC rules, even when the cheapest coax interconnects are used.

So he assumes 25 ns transport rise-time, and his math works to minimum cable length of 4' 8" (or longer) being preferred.

What is the typical min/max rise-time, for disc transports, in CD/DVD/blu-ray players?

Lessee... for 35 ns rise-time, the worst case would be the same coax cable (roughly 4.5') that'd likely be OK for a "typical" 25 ns rise-time. So 35 ns might need coax length of maybe 7 feet to lessen jitter issues with copper coax cables used for sending S/PDIF digital signal?

I mean, do 10% of current transport units average out at a slower 35 ns rise-time bracket?


Sadly, there is hardly any data on the rise time of signals out of S/PDIF devices. So no one can tell you what it is on any gear you may be using/buying.

As OtherSongs points out, there is as much data as one wants to measure or deduce from industry sources. Using the well-known equality Fc = 0.35/Tr

http://en.wikipedia.org/wiki/Rise_time

we get: Fc = 0.35/35 x 10**-9 = 10**7 or 10 MHz.

This is about the same spec as is given for SP/DIF output transformers that are used at 44 KHz, 16 or 24 bits. The extreme case is 24/192 where transformers wtih a bandpass of 28 MHz is used. The corresponding rise times would be about 10 ns. I believe that in general equpment equipped this way is considered "pro" equipment because it can't meet FCC Part 15 specs for consumer use, but it can meet FCC part 15 specs for professional use.
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post #41 of 53
5/29/12 at 12:51pm
Quote:
Originally Posted by diomania View Post

Since you seem to be having a hard time understanding my questions, let me expand it for you:

1. How did you discover that the cables came with the equipment was veering off of the standard impedance and have inadequate RFI shielding, did you measure them? If you did, what equipment did you use and how did you hook it up?

I never "discovered" it. Never said I did. Reading educates me that improper shielding or inconsistent impedance is not good for S/PDIF.

Quote:


2. You called it problems ("prone to impedance mismatch and RFI problems when used as S/PDIF") because you heard the difference? If you did, how did you set up the comparison rig?

Asked and answered. Never said I've heard the problem. I tend to spend a buck or two more for the correct cable. I also don't use socks for coffee filters, but reading suggests it won't work consistently.

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3. Let me ask you again with a hope that I will get some info on this, which gear is it that contained such problematic cables in the box?

Again, and I'll type slowly fer ya, not being in the habit of misusing provided cables (such as using R/W audio cables for S/PDIF cables) I can't help you out there. But if they are cheaply made cables with little shielding, they might be worthy of suspicion.

[I understand old underwear will work in a pinch as a coffee filter (if you're out of socks.)]
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post #42 of 53
5/29/12 at 2:35pm
Quote:
Originally Posted by domino92024 View Post

I never "discovered" it. Never said I did. Reading educates me that improper shielding or inconsistent impedance is not good for S/PDIF.

You have stated it. If you posted "according to *** writing, cheap, poorly shielded RCA analog audio cables are prone to impedance mismatch and RFI problems when used as S/PDIF." then it would have been fine but you didn't do that. Instead, you posted your take on the subject, "Cheap, poorly shielded RCA analog audio cables are prone to impedance mismatch and RFI problems when used as S/PDIF."

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Asked and answered.

No you didn't.
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Never said I've heard the problem.

I asked about hearing a difference. Who are you replying to? I sure didn't ask if you heard the problem.
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I tend to spend a buck or two more for the correct cable. I also don't use socks for coffee filters, but reading suggests it won't work consistently.

Who are you replying to? I didn't ask what you spend on cable or why and how you choose coffee filter.
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Again, and I'll type slowly fer ya, not being in the habit of misusing provided cables (such as using R/W audio cables for S/PDIF cables) I can't help you out there. But if they are cheaply made cables with little shielding, they might be worthy of suspicion.

You still can't name the gear?


Quote:


prone to impedance mismatch and RFI problems when used as S/PDIF

Why did you label it "problems" when you haven't heard the effects of it?
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post #43 of 53
5/29/12 at 4:04pm
Spend the extra dollar or two for a a 75 Ohm S/PDIF cable. No use in an argument.
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post #44 of 53
5/29/12 at 7:28pm
It is certainly not like an excellent cable will cost an arm and a leg. A six foot cable from BJC constructed with Belden 1694A and Canare connectors is less than $20. And perfectly adequate cables are available for less.
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post #45 of 53
5/29/12 at 10:34pm
Quote:
Originally Posted by diomania View Post

Why did you label it "problems" when you haven't heard the effects of it?

I wrote that they are "PRONE TO have problems." That means susceptible to or liable to. That doesn't mean that they always do, or that I have experienced such a problem. I don't misuse cables, just as I don't use socks or underwear for coffee filters. I haven't seem them have problems, but would bet that there's a reason coffee filters are made. Even the most dense understand that.

I guess...no, I won't go there.

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I asked about hearing a difference. Who are you replying to? I sure didn't ask if you heard the problem.

Oh, silly me. I assumed you would agree that a difference denotes a problem. OK...I've had enough of your foolery.
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post #46 of 53
5/30/12 at 8:59am
Quote:
Originally Posted by domino92024 View Post

I wrote that they are "PRONE TO have problems."

You are now changing what you wrote. You wrote, "prone to impedance mismatch and RFI problems when used as S/PDIF". Took dance lessons from amirm?

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That means susceptible to or liable to. That doesn't mean that they always do,

According to whom, yourself or whatever the writing that you are parroting? It would help the discussion if you can clarify it.

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or that I have experienced such a problem.

So you don't know yet.
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I don't misuse cables, just as I don't use socks or underwear for coffee filters. I haven't seem them have problems, but would bet that there's a reason coffee filters are made. Even the most dense understand that.

I guess...no, I won't go there.

Misuse? So now you are the one who defines the wording on electronic patch cables?
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Oh, silly me. I assumed you would agree that a difference denotes a problem.

Just like you assumed about the patch cables included with the gear is prone to impedance mismatch and RFI problems when used as S/PDIF.
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OK...I've had enough of your foolery.

Not mine.

It is clear now that you were just parroting something you've read (there are many including white paper from snake-oil cable company) but have no knowledge of this subject in real life situation. You couldn't even name one equipment.
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post #47 of 53
5/30/12 at 9:07am
No cable which uses RCA connectors is properly impedance matched to anything. That's "obvious" from basic electomagnetic transmission line theory as taught in college E&M physics courses.
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post #48 of 53
5/30/12 at 9:48am
Quote:
Originally Posted by Selden Ball View Post

No cable which uses RCA connectors is properly impedance matched to anything. That's "obvious" from basic electomagnetic transmission line theory as taught in college E&M physics courses.

It isn't just the RCA connectors used, *everything* in the circuit affects impedance.

That ref that amirm gave is worth reading if only for the impedance match/mismatch explanation: http://www.positive-feedback.com/Issue14/spdif.htm
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post #49 of 53
5/30/12 at 11:30am
Some cars are recommended that you use "premium" gas. If you fill the tank with "regular", it will still start and get you to where you need to go. Many individuals wouldn't know the difference.

Use whatever cable works if you really need to scrimp and save a dollar or two. It's not worth losing sleep if you're happy with the performance/sound.

Again! Why argue about this issue? The S/PDIF recommendation is 75 Ohm. Done deal.
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post #50 of 53
5/30/12 at 12:57pm
Quote:
Originally Posted by diomania View Post

You are now changing what you wrote. You wrote, "prone to impedance mismatch and RFI problems when used as S/PDIF". Took dance lessons from amirm?

So I shortened "impedance mismatch and RFI problems" to "problems." Your "problem" seems to be one of fear of being incorrect if that is the thrust of your retort.

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According to whom, yourself or whatever the writing that you are parroting? It would help the discussion if you can clarify it.

1. Try looking "prone" up in a dictionary.
2. Admit your error, and go bother someone else.

Plain ol' patch cord type analog audio RCA type cables are "prone to impedance mismatch and RFI problems when used as S/PDIF." Period. Bye.
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post #51 of 53
5/30/12 at 1:32pm
Quote:
Originally Posted by OtherSongs View Post

It isn't just the RCA connectors used, *everything* in the circuit affects impedance.

That ref that amirm gave is worth reading if only for the impedance match/mismatch explanation: http://www.positive-feedback.com/Issue14/spdif.htm

The reference looks more than a little alarmist to me. As I pointed out in another post, the consequences of an impedance mismatch depends on the length of the portion of the transmission line that is mismatched, how much it is mismatched, and the wavelength of the highest frequency involved.

A general rule is that anything less than 1/4 wavelength long and not extreme (either a short or an open) causes negligible standing waves or any other kind of significant problem.


If we pick 30 MHz as the highest frequency of interest, then 1 wavelength is about 10 meters or 30 feet. Pick 100 MHz, and now we are down around wavelengths of around 10 feet, and our 1/4 wave is still 30 inches.

Bottom line is that yes, RCA connectors aren't impedance matched, but they are so short as compared to the wavelengths involved that they are moot.
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post #52 of 53
5/30/12 at 1:50pm
Quote:
Originally Posted by jayfore View Post

I just bought a new Blu-Ray player from Costco. My existing one has optical audio out, which I have been using for years. The new player does not have an optical audio output -- just coax. OK, fine, I can deal with that... But do I need a special cable for it? Seems that any of my spare cables, like from the olden days (RCA type) fit just fine, but is there a difference in quality? I would guess there is. Further, if I should get one specifically designed for this, does it really matter which one I get? I am not looking to spend much money, but also want it to sound at least as good as what the optical cable already gives me. Coax audio cables can be found on Ebay for under $4 shipped -- are those fine?

Thanks!

A $4 coax cable from eBay should do just fine. The consensus here seems to be that pretty much any audio cable should work, too. It did not work for me the last time I tried it, but I cannot tell you why that was. I'd probably spend the $4 to be on the safe side, but I am funny that way.
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post #53 of 53
5/30/12 at 2:47pm
Quote:
Originally Posted by domino92024 View Post

So I shortened "impedance mismatch and RFI problems" to "problems." Your "problem" seems to be one of fear of being incorrect if that is the thrust of your retort.

You have a communication problem, written communication to be specific:

"I wrote that they are "PRONE TO have problems."" What you should have written instead is, "What I meant was, "PRONE TO have problems."". When you say "I wrote that they are "PRONE TO have problems."" after writing "prone to impedance mismatch and RFI problems when used as S/PDIF" makes it a lie because you didn't.
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Plain ol' patch cord type analog audio RCA type cables are "prone to impedance mismatch and RFI problems when used as S/PDIF." Period.

Period? Once again, according to whom, you or the writing you are parroting? You don't learn, do you.

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2. Admit your error,

I made an error? Can you quote it?
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