Do you believe in magic?
After reading holographic universe, I can almost grasp the idea of wave particle duality, (all part of the same quantum soup) and consciousness being an energy/ interference pattern in the soup(swirls?), but I stumble at the Copenhagen phenomenon , and when faced with complementarity, come unswirled.
Feel like the apemen staring at a big black monolith.😱
After reading holographic universe, I can almost grasp the idea of wave particle duality, (all part of the same quantum soup) and consciousness being an energy/ interference pattern in the soup(swirls?), but I stumble at the Copenhagen phenomenon , and when faced with complementarity, come unswirled.
Feel like the apemen staring at a big black monolith.😱
It's possible for a SPDIF cable that has some impedance anomalies at specific points along it's length to present different cable jitter spectrum at the receiving end, depending on which way it is connected. In this case it could well have a favoured direction.
With a homemade cable targeted toward nonexistent problems, constructed by someone with dim understanding, anything is possible.
Nope...its digital signal, it isn't gonna care, and how about signals going down PCBs, turn the cable round look at the scope, no different.
Huh? Does jitter not exist, then? Do you measure/analyse it with a scope?
High-speed signals on pcb traces are dimensionally better controlled, no?
Edit: I'm not advocating directionality in all cables simply stating a circumstance where directionality is possible
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Why start with the comment "does jitter not exist then" a bit silly...
Cable induced jitter on a good quality shielded cable at SPDIF frequencies, not to much of a concern, when you get to higher data rates it can be, but then at these rates impedance mismatches do become more important. Below 20+MHz (with a sensible rise time) your digital design will not be affected much by impedance mismatches, not to the extent that signal integrity issues come in to play. This does depend on signal rise time of course and the fad for silly rise times (ie to fast) is detrimental to the signal and does more harm than good.
No where in digital signal transmission have I ever discussed cable directivity, not has it ever been an issue, in fact the first time I heard of it was on this site...
As to PCB traces being dimensionally better controlled (here I presume you mean impedance controlled), no they are not and it is only when you start using DDR memory and gigabit Ethernet that impedance control layout and manufacture is used. Below that it is not required and is not done. The shape of the digital wave will also NOT give any indication of the resultant sound field.
As to 75ohm and SPDIF signals they really don't care that much about the impedance (caveat, sensible rise times) and in the past I have posted and done simulations of SPDIF signals, with mismatched impedances representing the PCB traces at both ends, the connectors and the cable, signal gets through OK and the eye diagrams showed there would be no problems.
So no cable directivity and digital signals is a myth, and has no effect.
SPDIF is not high speed....
??
What is this board? Have you used it before? I'm being tasked with sound control in a really bad building, the ground floor is nuttin but glass and beams. It takes about 3 days for an echo to die down.
jn
Nearly any reputable and non-exotic RG59 or similar coax from a major manufacturer (e.g., Belden) will be close enough to 75 ohms characteristic impedance that it's not worth worrying about. The stuff is made by the kilometer with very, very tight process controls.
Note that your cable TV works, and that's with much longer runs and much wider bandwidth.
Because you said "Nope...its digital signal, it isn't gonna care" which to me seems to say it's digital & therefore immune ("digital doesn't care" is a strange way of expressing it though)
But higher data rates & faster rise times are exactly the trends seen in digital currently so jitter is therefore a current consideration.
I've never seen mentioned anywhere except here, some of the issues that JN & others speak of ..... does this therefore nullify the issues?
Yes, PCB traces designed to handle high speed signals are dimensionally & therefore impedance controlled. If you are saying that transmission line considerations aren't implemented until GHz speeds, I think you will find many to disagree. I'm sure you will find many examples where signal quality considerations are paid attention to?
That would be relevant, If you said that you've tested with real world implementations (high sample rates & fast rise times) & found no problem in the results.
Approx 6Mhz is the stated bandwidth for 192Khz audio but about 5 times that bandwidth is needed for good signal transmission & a fast risetime will need the 9th harmonic so approx 60MHz is needed.
As I said already, I'm just giving a possible scenario where directivity could apply in SPDIF cables (given current real world considerations of cable construction consistency, high data rates, fast risetimes)
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I don't recall any of my stuff pertaining to wire directionality per se. There are ways to make it directional, but standard coax techniques like directional couplers aren't used in audio. I ignore the addition of passive components, that's a different beast.
jn
Actually, you don't need anywhere near that bandwidth, but if it makes people happy, it's trivially easy. After all, cable TV uses millions of kilometers of RG59, and has a bandwidth more than an order of magnitude higher.
This is a total non-issue.
No, I wasn't referring to any references you have made to cable directionality rather my comments were in relation to transmission line considerations & impedance mismatches, in speaker cables. You have shown the theoretical underpinnings for this but many discount the audibility of it.
I'm simply pointing out the possibility that internal cable construction tolerance margins (1% tolerance will allow a deviation of 7.5ohms anywhere along the cable) can give rise to a different jitter spectrum when used in one direction compared to another direction. Whether this is audible is another question but the possibility exists.
We are talking SPDIF not high speed digital design, irrelevant to a discussion on SPDIF. Jitter per say can be a concern but Audio takes it to the limit when you look at jitter figures and data rates. Now channel hopping radios is a different matter, or network communication (WIDE AREA), satellite communications, even the DDR memory interfaces, but its all catered for during the design cycle.
Read my reply, they are not until you start doing DDR memory, gigabit Ethernet or PCIe on board. I do know this for a fact, most boards that don't have these interfaces are not impedance controlled, nor are trace widths chosen to give a particular impedance, mostly they are chosen dependant of PCB density, company design rules.
Again I did not say GHz speeds I said that most designs do not have made or use controlled impedance PCBs until they really have to, again when you throw on DDR memory, gigabit Ethernet, etc. otherwise the boards are generically laid out with trace widths ranging from 0.2-0.1mm for standard signals and layer counts from 4+ to 12+. I do many high speed and critical designs, digital, RF, analogue....my experience is in the real world working with PCBs.
And why aren't simulations done on SIV software relevant for SPDIF, they are relevant for high speed critical designs? again higher speed stuff is not so relevant when we are discussing SPDIF.
Getting high speed signals from a to b is a BIG part of my job. I do high speed layouts where I have to use signal integrity verification simulation tools.
Suggest you look up knee frequency, derived from the rise time, this gives you the upper frequency you need to be concerned about.
Even with high speed interfaces cable directionality is not an issue, now some silly way out RF stuff can be a bit different, but again is irrelevant to this discussion.
More info can be gleamed from the likes of Howard Johnson, Eric Bogatin, Ralf Morrison, Henry Ott etc.
That's a HUGELY bigger deviation than you see in coax manufacturing. Spend a little time looking at production/monitoring equipment from companies like Maillefer.
When you say "jitter spectrum," may I assume that you're not talking about jitter in the only place it counts, at the DAC?
I'm pleased to see that all you chaps have been keeping the shop open while I have been away getting married!
As that request came from a moderator I will assume a limited licence to go OT!
The lady and I have been good friends for many years but last year saw the nature of our relationship change and develop. Six months planning a wedding ended on 5 April. Got back from honeymoon on Friday and now catching up with things again.
I may need tips from more experienced members on how to accommodate an electronic hobby and a non-techie wife in the same house!
The lady and I have been good friends for many years but last year saw the nature of our relationship change and develop. Six months planning a wedding ended on 5 April. Got back from honeymoon on Friday and now catching up with things again.
I may need tips from more experienced members on how to accommodate an electronic hobby and a non-techie wife in the same house!
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