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post #1 of 53 Old 05-26-2012, 06:15 PM - Thread Starter
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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!
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post #2 of 53 Old 05-26-2012, 07:08 PM
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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!

I assume this is a SPDIF connection... Any RCA cable should work. It's a digital signal so it doesn't have to be a special high quality cable.
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post #3 of 53 Old 05-26-2012, 10:17 PM
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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!

Cables should meet the S/PDIF specification as defined by the international standard IEC 60958-3 for assured performance. Cheap, poorly shielded RCA analog audio cables are prone to impedance mismatch and RFI problems when used as S/PDIF. The orange connector on S/PDIF cables isn't just pretty, they designate S/PDIF versus analog audio cables.
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post #4 of 53 Old 05-26-2012, 10:40 PM
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Any decent 75 ohm cable should work just fine, say 95% braid plus foil shield. But it might work just fine with any old audio patch cable.
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post #5 of 53 Old 05-27-2012, 01:22 AM
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A composite video cable (with yellow RCA plug) is also 75Ω and suitable.

Audiosceptics accept audio trials using 25 people. A recent Oxford study with over 353,000 patient records from 639 separate clinical trials shows for every 1,000 people taking diclofenac or ibuprofen there would be 3 additional heart attacks, 4 more cases of heart failure and 1 death every year.

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post #6 of 53 Old 05-27-2012, 04:30 AM
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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?

Not unless your cable is exceptionally long. For the usual lengths that this cable is in a home audio system (3 feet or less), the application is generally very non-critical.

To demonstrate the non-critical nature of this connection, crative people have used coat hanger wires, Christmas tinsel, and even wet the forefingers on each hand and bridged the connection with their bodies. Under some conditions, they all can work! I've tried several of these myself.

Quote:
Seems that any of my spare cables, like from the olden days (RCA type) fit just fine, but is there a difference in quality?

Again, it depends on the application. One of the nice things about digital is that problems with cabling generally fit into one of two categories - they work very well, or they don't work at all. There are exceptions but they are relatively rare.

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I would guess there is.

If you understand the relevant technology, guessing is vastly reduced.

Quote:
Further, if I should get one specifically designed for this, does it really matter which one I get?

"Designed for this" expressed technically is: "A 75 ohm coaxial cable with RCA male connectors on each end". This is the same thing as some video cables with yellow connectors that one finds for sale in places that sell A/V cables.

Quote:
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?

You must be looking at the high priced items! I found cables for as little as $0.99 including shipping that would probably do the job. Of course, you didn't specify length.

Thanks![/quote]
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post #7 of 53 Old 05-27-2012, 08:36 AM
 
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Quote:
Originally Posted by domino92024 View Post

Cheap, poorly shielded RCA analog audio cables are prone to impedance mismatch and RFI problems when used as S/PDIF.

Which brand and model caused this problem? And what did it sound like when this happened?
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post #8 of 53 Old 05-27-2012, 10:45 AM
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Quote:
Originally Posted by diomania View Post

Which brand and model caused this problem? And what did it sound like when this happened?

As stated above, SPDIF should be run over true 75ohm coax cable. A RadioShack "yellow" video cable is all you need. And as also stated, for under six feet, any old audio grade RCA cable should work just fine. While not 75ohms, at this length it's not critical.

If there is a cable issue you will hear dropouts, ticks, and cracks. You WILL NOT hear a higher noise floor, distortion, or altered frequency response. These things don't happen with digital signal transmission.

IOW, if you get tick and click free audio, that's as good as it gets. A more expensive cable will make no difference.

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post #9 of 53 Old 05-27-2012, 10:48 AM
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Originally Posted by domino92024 View Post

Cables should meet the S/PDIF specification as defined by the international standard IEC 60958-3 for assured performance. Cheap, poorly shielded RCA analog audio cables are prone to impedance mismatch and RFI problems when used as S/PDIF. The orange connector on S/PDIF cables isn't just pretty, they designate S/PDIF versus analog audio cables.

You talk like an electrical engineering student! And that's great. No offense intended. But in real world applications, you can abuse SPDIF quite a bit before it fails.

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post #10 of 53 Old 05-27-2012, 11:07 AM
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Quote:
Originally Posted by Glimmie View Post

If there is a cable issue you will hear dropouts, ticks, and cracks. You WILL NOT hear a higher noise floor, distortion, or altered frequency response. These things don't happen with digital signal transmission.

IOW, if you get tick and click free audio, that's as good as it gets. A more expensive cable will make no difference.

That's the key. A wire carrying digital audio either works or it doesn't. Anyone who tells you otherwise is...probably trying to con you into buying something you don't need!

The best advice for the OP is to try one of the wires s/he has on hand (assuming s/he has one that is the appropriate length) and if it doesn't have any readily- audible issues, worry about something consequential. If it does have issues, then look for something that's stated to be a 75Ω cable.

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post #11 of 53 Old 05-27-2012, 01:29 PM
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Quote:
Originally Posted by Glimmie View Post

If there is a cable issue you will hear dropouts, ticks, and cracks. You WILL NOT hear a higher noise floor, distortion, or altered frequency response. These things don't happen with digital signal transmission.

IOW, if you get tick and click free audio, that's as good as it gets. A more expensive cable will make no difference.

Well said.
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post #12 of 53 Old 05-27-2012, 02:32 PM
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Originally Posted by Glimmie View Post

You talk like an electrical engineering student! And that's great. No offense intended. But in real world applications, you can abuse SPDIF quite a bit before it fails.

And in the real world, most consumers wouldn't notice the change in sound due to square wave rounding (impedance irregularities), or RFI induced distortion. Minor degradation would go unnoticed by most, leading to the "either it works or it doesn't" advice. That's fine. I just point out the cable specification for those that care to look at it. For a buck or two difference and a multi-year lifespan, I'm sure not going to try to save a buck here.
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post #13 of 53 Old 05-27-2012, 02:38 PM
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Originally Posted by arnyk View Post

You must be looking at the high priced items! I found cables for as little as $0.99 including shipping that would probably do the job. Of course, you didn't specify length.

99 cents including shipping? Without ordering $25 or so of stuff you don't need? Where?
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post #14 of 53 Old 05-27-2012, 03:05 PM
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Quote:
Originally Posted by Glimmie View Post

If there is a cable issue you will hear dropouts,...

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.
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post #15 of 53 Old 05-27-2012, 03:49 PM
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Quote:
Originally Posted by domino92024 View Post

And in the real world, most consumers wouldn't notice the change in sound due to square wave rounding (impedance irregularities), or RFI induced distortion. Minor degradation would go unnoticed by most, leading to the "either it works or it doesn't" advice. That's fine. I just point out the cable specification for those that care to look at it. For a buck or two difference and a multi-year lifespan, I'm sure not going to try to save a buck here.

So are you saying the round off of the data pulse risetimes or RFI below the data threshold makes an audible difference [with an SPDIF cable]?

If so you're going to have to explain that to this 25yr practicing EE!

Now with an analog cable, such is quite possible.

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post #16 of 53 Old 05-27-2012, 03:57 PM
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A digital audio interface is not just "digital." It conveys both sample data and timing for it with the latter being analog data, not digital. You get sound when the digital part works. You get the best performance when the timing is correctly conveyed. Getting the former does not indicate the latter is also there. Don't confuse this interface with digital ones used for computer data where digital data remains digital at the other end.

As I note in this article on digital audio links digital audio cables can make a measurable difference in the output of your system as non-intuitively it might seem. You may not hear the difference but it can show up in measurements. Here is a graph from that article specifically on the use of (long) audio cable and how it can change teh zero-crossing point that is used to extract timing:



The graph did not come from some crazy audiophile magazine but Audio Engineering Society recommendation on digital audio interface.

All this said, if you just want sound out of the thing, hook up any cable that produces the same. Coat hanger is indeed fine if that is your goal. If you want to do better and still save a bundle, then as stated get a video cable, not audio. If you want to do better get a proper cable and avoid 1 meter/3 foot length. Reason for that is here: http://www.positive-feedback.com/Issue14/spdif.htm

Finally, if you wanted to read more than you possibly wanted with detailed analysis by a DAC designer, click on the first link in this Google search: https://www.google.com/search?rlz=1C...dth+and+Jitter

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post #17 of 53 Old 05-27-2012, 04:14 PM
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"You may not hear the difference but it can show up in measurements."

And that's a key point! Not too many people can hear true 24 bits.

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post #18 of 53 Old 05-27-2012, 10:25 PM
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Quote:
Originally Posted by Glimmie View Post

So are you saying the round off of the data pulse risetimes or RFI below the data threshold makes an audible difference [with an SPDIF cable]?

If so you're going to have to explain that to this 25yr practicing EE!

Now with an analog cable, such is quite possible.

I am discussing the possible results when using an analog cable (the cheaper the more likely, of course.) As far as being audible, how bad is the degradation? How bad is the RFI? How educated are the listener's ears?
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Originally Posted by domino92024 View Post

I am discussing the possible results when using an analog cable (the cheaper the more likely, of course.)

Analog cable to send S/PDIF data?

Can you tell me which brand and models are "Cheap, poorly shielded RCA analog audio cables are prone to impedance mismatch and RFI problems when used as S/PDIF."? It would be helpful to know so I can avoid them and also warn others I know. Thanks in advance.
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post #20 of 53 Old 05-28-2012, 03:40 AM
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Originally Posted by domino92024 View Post

99 cents including shipping? Without ordering $25 or so of stuff you don't need? Where?

Ebay. There are a ton of people in China who are shameless - they will ship you an amazing selection of really pretty good stuff in small quantities with negligible shipping fees. Your cost is that you have to wait a week or two for the stuff to show up.
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post #21 of 53 Old 05-28-2012, 03:50 AM
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Originally Posted by domino92024 View Post

I am discussing the possible results when using an analog cable (the cheaper the more likely, of course.) As far as being audible, how bad is the degradation? How bad is the RFI? How educated are the listener's ears?

I can tell you about the degradation. It ain't that much if viewed on a 'scope if the cable is a typical audiphile length - 3 to 6 feet.

It turns out that any FCC Part 15 compliant consumer SP/DIF output is going to be low-pass filtered around 10-15 mHz in order to be compliant.

A typical analog interconnect is shielded well enough, but it probably has a characteristic impedance of more like 110 ohms than the desired 75 ohms. This is not a really bad mismatch. I wouldn't tolerate it in a high-powered radio transmitter, but impedance mismatches like this are tolerated in receiving and low powered transmitting systems all the time.

One of the industry rules of thumb of transmission line impedances is that if a a transmission line (e.g. a cable) is less than 1/4 wavelength at the highest frequency being transmitted, its characteristic impedance matters very little. This is BTW a highly conservative rule. I've checked it out with some of the pickiest mixed-signal circuit board designers in the business.

The wavelength of 15 MHz is about 65 feet. Any cable under 15 feet therefore meets the 1/4 wavelength rule. Since the mismatch isn't all that bad, and the rule is highly conservative, even 100 foot analog audio cables would probably be OK.

A friend who is an electrical engineer actually tried running SPDIF over 100 feet of 300 ohm twin lead, and it worked just fine. Now that is a long line and a serious mismatch!
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post #22 of 53 Old 05-28-2012, 08:56 AM
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Originally Posted by diomania View Post

Analog cable to send S/PDIF data?

What other kind of cable is there? Cables are analog devices. Take any "digital" cable and send it analog audio. You think you get ones and zeros and not audio?

Quote:


Can you tell me which brand and models are "Cheap, poorly shielded RCA analog audio cables are prone to impedance mismatch and RFI problems when used as S/PDIF."? It would be helpful to know so I can avoid them and also warn others I know. Thanks in advance.

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.

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post #23 of 53 Old 05-28-2012, 10:40 AM
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Originally Posted by amirm View Post

What other kind of cable is there? Cables are analog devices.

Even fiber!

I had some low cost analog video fiber links in the 1980s that used video amplitude modulation - AM. So the video levels were directly related to the light level of the laser LED. These simple circuits hardly produced the best quality but it shows fiber too can be used with analog transmission. Of course high quality analog fiber transmission uses FM. Digital is inherently FM too.

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post #24 of 53 Old 05-28-2012, 11:17 AM
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Quote:
Originally Posted by diomania View Post

Analog cable to send S/PDIF data?

Quote:
Originally Posted by amirm View Post

What other kind of cable is there? Cables are analog devices.

The main thing about a "digital" coax RCA interconnect cable is that it has better shielding, and better shielding generally makes the cable fatter and stiffer and more expensive.

Already this thread suffers from information overload from the usual AVS crowd, so I was surprised to see you post. I mean the OP quickly disappeared. I suppose I could understand it if the OP had posted a 2nd time and given just the smallest sense of interest in high sound quality.

I did find your ref to "S/PDIF Digital Cable by Steve Nugent" (i.e. it's length) to be interesting.

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Simple answer (without graphs and BS). Digital Coax audio interconnections recommend a 75 Ohm cable. Spend a few extra bucks and get the proper cable. That eliminates any question(s).
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post #26 of 53 Old 05-28-2012, 12:20 PM
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Quote:
Originally Posted by diomania View Post

Analog cable to send S/PDIF data?

Can you tell me which brand and models are "Cheap, poorly shielded RCA analog audio cables are prone to impedance mismatch and RFI problems when used as S/PDIF."? It would be helpful to know so I can avoid them and also warn others I know. Thanks in advance.

Ah...sarcasm. It doesn't become you. But, I'll bite. R/W patch cords included in equipment boxes. Rarely marked with a brand. Cheap cables rarely are.
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post #27 of 53 Old 05-28-2012, 12:24 PM
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Originally Posted by Glimmie View Post

...Not too many people can hear true 24 bits.

24x6=144dB, and if you do ever hear that it will probably be the last thing you ever hear.
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post #28 of 53 Old 05-28-2012, 12:25 PM
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Quote:
Originally Posted by arnyk View Post

Ebay. There are a ton of people in China who are shameless - they will ship you an amazing selection of really pretty good stuff in small quantities with negligible shipping fees. Your cost is that you have to wait a week or two for the stuff to show up.

Just checked Ebay. Alas, I could find no coaxial/RCA cables for $0.99 including shipping. You must have gotten them all.
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post #29 of 53 Old 05-28-2012, 02:38 PM
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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.

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?

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Originally Posted by domino92024 View Post

R/W patch cords included in equipment boxes. Rarely marked with a brand.

They cause "impedance mismatch and RFI problems"? How did you become aware that it was a problem? Also, which gear is it that contained such problematic cables in the box?
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