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65.28.169.41
In Reply to: RE: Recommedations Digital Cable 1.5M $200 posted by jllaudio on August 12, 2012 at 06:47:41
I stuck on a 25 ft 75ohm cable just for the heck of it. works better.
Just sayin'.
Follow Ups:
The reason is that what triggers any digital audio signal is a transition (ie, "zero" to "one" and vice-versa). With a normal length of digital cable (like 1.5 meters) ANY reflections due to impedance mismatches at either end (and these are INEVITABLE) will come back while the digital audio receiving circuitry is changing signal states (ie, "zero" to "one" or vice versa), causing the receiving circuit to interpret this added reflection as jitter.
On the other hand, if you use a cable of 25' or more, the transition will be long over by the time any reflection comes back to mess up the original signal.
Now there is a new problem (actually an old problem that becomes somewhat more important), as the cable itself must be high quality so that its impedance is constant throughout its length. This requires the cable to be manufactured to closer tolerances physically (which affects the impedance, inch-by-inch). Otherwise there will be reflections at every point in the cable where ever the impedance changes. (Don't put sharp bends in your cables.)
But these impedance changes are much smaller than the ones found at the input and output of digital audio equipment. It also doesn't cost that much for the cable manufacturer to purchase high-quality cable made to close tolerances. I would never use S/PDIF without also using a long cable.
It's Blue Jeans Cable's Belden 1694A with compression attached Canare RCAP connectors. See link below ...
... Keynes, Galbraith, Samuelson, Shiller, Reich, Stiglitz, Krugman, Singh
Whatever happened to the shorter the signal path the better? That is what I was always told regardless of type of signal. I also use a 1.5m Wireworld Starlight 6 coax which seems to give me fine results. Should I now instead order a 10m length, loop it around my room a couple times before feeding it to my Dac and expect to get better results? I'm starting to question my sanity at this point!
I ran this theory by the owners of two top shelf cable companies...they advertise in stereophile every month..and they thought this was complete bunk.
One supplies cables to the Navy as well for high level communications as well.
Those two guys are either right or wrong. Just because they advertise in Stereophile every month doesn't mean that they know squat about cables. It does mean that they run profitable companies. There used to be a lot of people like that that bought off-the-shelf cable and sold it for 10x the price.
The guy that told me about this was an RF engineer with a TDR. He made some of the world's best sounding digital gear before he got cancer and couldn't work any more. I have listened to his cables and believe that his theory is correct. This is one of those things that *almost* falls into the category of "one measurement is worth a thousand expert opinions".
I say "almost" because most measurements don't correlate with sound quality, although this is one that does. And also I have no idea how "expert" the two opinions you received were. I have much more respect for some people's opinions than other's.
Hi Mr Hansen:The only reason I mentioned the fact that these two companies advertise in the magazine is illustrate they are established. I am not naming them because their opinions were offered in private conversation. Suffice it to say they are not one of the flashier cable companies around.
But back to the theory of digital cable length, both told me through thorough experimentation and testing they could find no evidence of shorter lengths exhibiting the theoretical issues you talked about. They even went on to say they WISH it were so they could advise their dealers and customers as such and sell much longer digital links and make a hellava lot more mulah.
For the record, I have no idea who is right,but I would to see you pass a blind test on 1 meter cable and a 25 foot one. :)
Edits: 08/28/12
> > For the record, I have no idea who is right,but I would to see you pass a blind test on 1 meter cable and a 25 foot one. :) < <
First of all, I would never do such a thing except for myself. I am not a trained monkey doing tricks on display. Second of all I do a lot of listening tests, probably about 1/3 of them blind. They are definitely harder, but just because of the pressure rather than any inherent difference. I do it as a way to keep myself on my toes and make sure that I'm not drifting into la-la land. Third of all, I cannot explain the experiences of the cable manufacturers. Maybe they are deaf. Or maybe I am deaf. Maybe their system can't resolve that kind of difference. Or maybe I am deluded into thinking that mine can. Or maybe their cables have so many reflections already that you can't hear a few more. I have no idea. If I spent some time with their systems I could probably provide some more opinions.
But if you look at the entire thread, there have been several people that tried longer cables and heard significantly better sound. I would recommend that you just try it yourself. Have fun@
Wow..maybe all those scenarios are true!
Unfortunately, I won't be doing any testing.
First, my streamer is 3 feet away from DAC... secondly,
The cost of a 25 foot optical, AES/EBU, or coax cable
would break the bank.
Lastly I have never seen a demo, dealer set up, or a reviewer reference with any thing other than standard length digital cables of any flavor.
I don't know how good these are, but they have a good buzz, are perfect for a test like this, and they are stupidly cheap.
Blue Jeans Cable makes a 3' BNC-BNC for $16 while an identical 20' cable is $28. Total cost to run the experiment? $44. Plus you will have two usable cables.
If these don't have enough cache for you, they offer ones with teflon insulation for about 50% more money. I won't be trying it because I don't have an S/PDIF DAC. But I invite you to try it and let us know what you hear. My guess is that your opinion of the two cable manufacturers will lessen.
Ok, let's remove the affordability issue, as you have clearly illustrated there are inexpensive options.
So what do I do with 25 feet of cable behind my rack?
I guess what I am saying is even if there is a 5% improvement, and that is being generous, is it worth that kind of inconvenience?
Well, what would you say if the improvement was closer to 25% than 5%?
There is absolutely no way to quantify the "improvement" other than hauling out more quotes from so called experts.
If you could prove that big a difference I would vote for that turd Romney. That is how confident I am.
Again, never seen a 25 foot digital cable after attending a hundred audio shows, demos, and dealer events.
Posted by Charles Hansen (M) on September 03, 2012 at 02:20:35
A single 20' cable will cost you $28.
Break the piggy bank and spend seven days with it in your system. (This will give it a couple of days to break in and then a few more to get used to it.) Then replace it with your short cable and tell me what you think.
It won't be a fair experiment because I'm sure that the sales tax on your current cable was more than $28, but you seem too tight fisted to spend the extra $18 to order a 3' cable and make it a fair comparison.
Then if I am wrong you can post to the entire world what an idiot I am and that nobody should ever listen to me. Instead it is better to get all your information by looking at the equipment set ups in audio shows.
Hell if I weren't such a tight wad I would offer to pay you the money back for your cables if I was wrong. But tough luck. I am feeling cheap tonight. Besides you might end up voting for that turd Romney, and that is something slightly more important than the sound of digital audio cables...
Sorry Charles:
But Mr Art Dudley, who loved your QB-9, simply did not hear it.
"I asked to borrow the following: a 1m USB cable, a 5m USB cable, a 1m audio interconnect pair, and a 5m interconnect pair. You can see where I'm going with this, I'm sure: I compared the sound of my computer-music system with the long USB cable and short interconnects (with the Ayre D/A next to my preamp) against that with the short USB cable and the long interconnects (with the Ayre on a sturdy wooden table next to my iMac). The difference was subtle but audible, and clearly favored the setup with the short USB cable."
http://www.stereophile.com/content/listening-103-page-3
Ummm, I thought you guys were the discussing SPDIF cables, not USB cables. I don't think the USB packets are as cranky nor given to symbol induced jitter. AND, from all I've read, the Ayre DAC is especially well buffered.
Rick
If the discussion was limited to SPDIF cables, then Mr. Dudley's quoted opinion has no bearing. I thought digital cables all transmit the same data.
Shows what I know.I somehow thought Mr. Hansen was including USB cables because he referred to his own system, in which he stated he uses his own USB DAC.
Edits: 09/03/12
Mr. Hansen:
First, I have no doubt there may something to your theory. However, a 25% difference? Doubt it. Even if there was no difference I could perceive, I would not tell people you are an idiot. Far from it.
To tell you the truth, it is not so much the money, but I am just thrilled with the sound of my system, and most importantly, I am TOO damn lazy to conduct an experiment and report back.
No to mention it would really only be legit if the two lengths of cables were of the same brand and flavor.
"So what do I do with 25 feet of cable behind my rack?"
Tony is tidy. Rick is unruly.
But in thus case an unruly cable will have less of an aperture for stray fields to induce longitudinal currents and doesn't risk impedance bumps due to deformations from the tie-wraps.
If you go for tidy, leave the tie-wraps loose.
Rick
Yeah, keep those tie wraps loose. And no, I'm not tidy, but given the question I figured that my answer ought to keep tidiness in mind.
I am of the random rat's nest, spaghetti wiring, school. The downside is that it has a tendency to lead to cursing every few months when it is necessary to rewire things due to new components, etc.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Thank God I thought I was alone in this regard.
I am a neat freak, and this simply would not do..:)
The outside world is swirling in chaos. But I can control what goes on in my dwelling, and that means organization of the highest order.
" So what do I do with 25 feet of cable behind my rack?"
Coil it up neatly securing the coil in place with plastic cable ties. Take care not to bend the cable on too tight a radius (depends on model of cable).
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
To tell you the truth, I am perfectly happy with my 1 Meter TosLink cable.
I don't have 25 foot digital cables. I don't have dedicated power lines terminated with audiophile wall outlets in my listening room. Nor do I have multi-thousand dollar interconnects and speaker cables! I don't even have really ugly $200,000 speakers! I suffer the additional dubious distinction of being a musician which, according to Sudz means that I have a lousy stereo, and according to Disbeliever, I'm not a good judge of sound. All this, and yet, here I am, really, really, really enjoying music! Imagine that! If you can. :)
I am officially confiscating your audiophile badge!!!
...waxing poetic about sparkling transients and lifted veils, can I get it back? Oh, never mind - just go here and have at it...
When in doubt, this always works for me... (Open in New Window)
I will tell you what.. I will reinstate you if you promise to wallow in blacker backgrounds, instruments hanging in space, airy highs, liquid midranges, and jaw dropping organ bass pedal notes.
Somehow I don't believe that a 25 foot coax cable can possibly break the bank. It it could, you probably won't be able to pay the electric bill to run the computer you use to post here. Ditto for the other types.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
All this talk of light/signal propagation made me think of this video. It's easily one of the coolest presentations I've seen, you guys/gals will probably appreciate it.
http://www.youtube.com/watch?v=Y_9vd4HWlVA
Also, nice to see another RF engineer on here! Nothing like having a TDR to track down VSWR issues. :)
When I was doing scientific research--measuring correlations among nuclear events (specifically, the emission and detection of two gamma rays)--we needed delays to allow one signal to catch up to another, but it had to be very precise. Rather than using an electronic delay, we used hundreds of meters of coaxial cable, for precisely this reason. Even with sophisticated laboratory equipment, reflections due to impedance mismatch could complicate fast, sensitive measurements.
Jim
Thanks to Elizabeth and you Charles. My current cable is only 1M and I thought going to 1.5 would be beneficial. It looks like I was heading in the right direction only way under estimating the actual benefit vs. length parameter.I used to Rep Copper TDR's and OTDR's when I was much younger and everything you've said makes a lot of sense concerning reflections.
Thanks,
Edits: 08/13/12
1.5m should be sufficient in most cases. Risetimes are usually 25nsec or faster. The first refection is the important one.
See:
http://www.positive-feedback.com/Issue14/spdif.htm
I agree that the first reflection is the most important one, as it is the largest one.
I disagree that the "average transport" (whatever the heck that is) has an average rise time of 25 nsec. In fact I remember about 10 years ago when Hi-Fi News measured a Theta DVD player and measured a risetime on the the S/PDIF output of around 3 nsec. This is about what I measure on our digital audio products also. So we are already off by around an order of magnitude.
Light in a vacuum travels about 1 foot per nanosecond. In a copper cable it is about 75% to 80% that speed (typically). So if a cable is 3 feet long long, each trip will take roughly 4 nanoseconds. Then three trips means the first reflection will arrive around 12 nanoseconds after the original signal. Depending on the circuitry in the transport and the DAC, this could be in exactly the right time range to screw up the original signal. It will all depend on the circuitry of the transport (mainly) and the DAC (partly).
On the other hand, using a longer cable of say 8 meters (25 feet) will change the time of the first reflection to around 70 nanoseconds and there is no possibility of a problem with CD. Even cutting it in half to 4 meters would give a much better chance of good sound with a broader range of equipment. But going to 1 or 1.5 meters is almost like asking for trouble.
I wrote that the first reflection will arrive 12 nsec after the original signal. This is not quite right. While it is true that the first reflection will arrive 12 nsec after the original signal is *transmitted*, it will arrive only 8 nsec after the original signal *arrives* at the receiver.
This secondary signal will then happen at almost the perfect time to disrupt the signal from most digital audio sources. One is much better off to use at least a 5 meter or longer cable to avoid these sorts of problems altogether.
Nice sq pop. Thanks Charles. I put in a 4 meter extension to my 1 meter spdif cable (I know adapters are not good) and it sounds very very good.
means that most excess length will be coiled: won't this hinder the transmission?
Also, is this visible in reflectometers?
Stu
I am an RF engineer - and to really understand what's going on you would need to use a Time domain reflectometer - you put a pulse down the cable and you will see every reflection as the signal goes down the line. In my experience the largest reflections will come from the connectors and adapters, less so cable bends unless they are excessively tight. And based upon empirical experience of sound, this makes sense.I have not seen normal cable bends creating more reflections - and with an eye diagram (a way of demodulating the digital on a scope and measure timing errors, clock errors, etc.) you see any small effect getting swamped out entirely by connector, clock and other effects. However if you violate the manufacturer's "minimum bend radius" you will see problems form that bend. And since the cable may be damaged, it may never come back once it has gone past that radius. A cable won't generally naturally lay in that sort of radius - you usually have to force it - and if you do the cable pinches, and the geometry deforms - sometimes permanently. If you don't know what it is, normal use will be fine - just don't force the cable into a tight bend or routing and you shoudl be 100% fine 100% of the time.
Also ...
A good impedance match is not always reflection free(*) - the design of the connectors and the method of attachment will influence this. If you could have a reflection free 75 Ohm cable - then the musings on the right length would be a non issue as it would not matter. BNC connections are generally pretty good if specified into the upper UHF to low microwave ranges. RCA connectors won't be good - even "true 75 Ohms" connectors if hooked to a typical SPDIF input won't be good.
SO my rules for coaxial RF cables for SPDIF:
1. Connectors - BNC first and specified to 1-6GHz somewhere.
2. Cable type - Specified to Microwave range (3-10GHz) with high coverage shielding. Skinny with a very narrow minimum bend radius.
3. CRIMP connections before solder. Passive Intermodulation is the only working theory for this - since multiple solder connections can be poor for this - and a good solid crimp may be a better interface.
5. Adapt from BNC to RCA - and if you have "True 75 Ohm" adapters it should work good. But don't sweat it too much - since the RCA connector itself may be a source of issues.
I use a Squeezebox into a Berkeley audio DAC right now - I have a homebrew cable at about 1.7m, and I also have a "Black Cat Silver Star" which is 1.23m - both sound great. I had an Audioquest cable that was "ok" but overall somewhat crummy and expensive. AQ I have egenrally liked for analog - but not SPDIF!However the RCA on the SB end of it doesn't make an intimately tight connection. I haven't noticed a large effect in poor sound with one that is tighter (but not 75 Ohms) and looser (and is true 75 Ohms)- but I suspect that if I were to correct this with a hardware mod to the SB, I am sure there will be a marginal improvement.
The SB is a great source - but the source itself isn't perfect - and there will be power supply noise, etc, that once you have a cable you are happy with that you may want to address before fussing with more cables. (I also have a Sonos - and use it for a casual whole house audio. In addition to not being bit perfect, it is very jittery - the SB is head and shoulders better than that)
(*) It is possible to have a perfect match hand still have large reflections - in many connectors they use various size and phase of reflections from various parts to create an overall match when they all ring back and forth.
"Knowledge is knowing that a tomato is a fruit. Wisdom is knowing not to put it in a fruit salad"
Edits: 08/26/12 08/26/12
.
.
It's rewarding (and very rare, unfortunately) when theory leads to an actual improvement in sound quality. I'm glad that worked for you. Try taking out the first meter and adapter and just going with the 4 meter cable. There is nothing magic about 5 meters. I think 4 meters will give you pretty much all of the advantages without the disadvantages of using two different cables plus an adapter.
As always, please let us know what you find out. Thanks!
Unfortunately the other 1.5 meter cable is hardwired into my Buf32s dac. But no matter adding the 4 meters made a substantial difference for the better.
Thanks for the update.
Won't a very long cable have a reduced bandwidth which will round off the square wave edges making a more difficult job for the receiver to retrieve the clock and determine the bit values?
At the lengths we are talking about dispersion shouldn't be an issue.
"Knowledge is knowing that a tomato is a fruit. Wisdom is knowing not to put it in a fruit salad"
No, you would have to get to hundreds of feet of cable for these effects to become problematic.
Any pictorial depiction?
And does this "reflection" problem also plagues spdif/toslink and st (with bnc terminals) optical cables?
Its like a "bounce" of the signal edge from the destination back to the source and then back to the destination, like a ball ricocheting from one wall to another and back again.
You will probably be familiar with these reflections in the form of "ghosts" on analog TV signals. The link below has an animation of this effect.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Thank you very much.
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