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Just a quickie before i go to RS tomorrow!

Discussion in 'Cables & Switches' started by Quicksilver25, Sep 2, 2005.

  1. Quicksilver25

    Quicksilver25
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    I am connecting my DVD player to my plasma panel via Component.
    Thats video sorted.. :thumbsup:
    If i connect the DVD player to the Panel via coaxial digital out will this provide digital audio to the panel?
    I am also connecting the DVD player to my DTS Amp via optical.
    Would there be a conflict?
    Any help to clear this up for me would be great! :smashin:
    Cheers,
    Q.
     
  2. rdhir

    rdhir
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    not heard of a panel having coax digital in for sound. It would be very strange if it did.

    Leave it connected to your amp digitally and use the amp speakers. That's what most people do.

    Hifi people recommend that you use the coax rather than optical, as the signal has 2 less conversions that way. Optical is recommended is you think you environment is susceptible to RFI (Radio Frequency Interference), or you use a poor quality ie unshielded coax cable.

    (Good quality means £20 not £200 -Profigold is an example of a decent make)

    Cheers

    Rajiv
     
  3. BDCSTENG GARETH

    BDCSTENG GARETH
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    I dont know why because this is the same signal but buffered through LEDs and the reverse to recieve!

    Any coax will do! a 50p phono cable will be fine, for a short distance! Build quality will be better (you'd hope) the more you pay... but if its hanging behind your rack - who cares? If you get a sound through the system, then the digital link its working 100% If there is no sound, the system is working 0% (doesn't really happen for 99% of domestic installs).
     
  4. rdhir

    rdhir
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    There have been more than a few people on these forums with cheap cables which exhibit RFI. It shouldn't happen I know.

    Anyway Profigold is a relatively cheap solution which is easily available, and I don't know many place to buy something decent for 50p.

    Well the theory on optical vs digital is that while it should be an identical conversion, in reality it adds extra delay which exhibits itself as jitter on the signal, so the bitstream is ever so slightly slower.

    Is this true? I don't know but plenty of people swear by having a clocking signal to avoid this in high end equipment eg TAG Sync Link.

    In the meantime, I personally don't see the point in optical unless there is a good reason such as RFI.
     
  5. BDCSTENG GARETH

    BDCSTENG GARETH
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    How have these people diagnosed that ther are suffering from RFI on their digital interconnect? It won't affect the digital signal, and if if does, they would get nothing at all!

    You can get phono cables from a market for example... If using for analogue, this is a different story... with digital cables, if the signal travels down some damp string or dentle floss, I'd use that!

    You are missunderstanding the term "jitter"
    Jitter is used when describing the timebase stability of a digital signal. If the conversion form SPDIF - optical did cause a delay, this would just be a delay (although there is no disernable delay). This could not be described as "jitter" as the delay would be constant, and therefor not be unstable.


    Nor do I, but TOSLINK optical cables look cool though...


    Regards,

    Gareth.
     
  6. CDphobe

    CDphobe
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    Can someone explain to me how the format/encoding for digital links has changed over the life of (say) Red Book format? In the "good ole days" of early CD players, using digital coax links between transport and DAC, there were ways of measuring the number of errors that the DAC had to resolve, clearly indicating that less than 100% transmission of the digital signal still resulted in an acceptable audio output. What's changed that its an all or nothing now?

    Al
     
  7. BDCSTENG GARETH

    BDCSTENG GARETH
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    What this is about concerns propication errors, not read errors.

    1's and 0's into a cable = 1's and 0's out! no question. There is a no-mans land where the "digital eye" gets smaller than the specified noise and jitter closure for the format. At this point you get catastrophic failure i.e. sky TV when it rains, poorly terminated cable (plug hanging off, not cheap)

    Errors from in the process of reading/recovering data from a CD is another matter entirely.

    Gareth.
     
  8. CDphobe

    CDphobe
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    Thanks for the additional info Gareth, but that still doesn't explain how, on a repeatable basis, the volume of errors being corrected for a disk could change depending on the cable used between the transport and DAC? Is it possible for noise on a cable to result in a 0 being "changed" to a 0.something over the transmission period through external influence, hence resulting in a correction being noted?

    Al
     
  9. BDCSTENG GARETH

    BDCSTENG GARETH
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    What equipment were you testing with?

    Im not too hot on CD technology, Im a tape person myself...(when it comes to knowing how the whole thing works).

    I cannot stress enough the theory behind the stucture of sending 1's and 0's down a cable, and measuring the jitter and noise.

    I cannot explain something which I have no evidence of infront of me!

    Thats not a get-out, but I'd be interested in some more information.

    Ive had a thought...

    Im going to get a cheap cable, and an expensive cable (loan from richer maybe) and do some stress tests... HF, LF, ramps etc.

    I have equipment here with me at work (yes Im working on a weekend :boring: ) and I could run high bandwidth data from a test generator to a test set and plug different cables in between and verify the results.

    Maybe if this works really well, we can sit back and chew the cud over the results of the readings?

    Its easier for me to run video here, but as its 75ohm, should hold up to the critics. Available to me here, I have everything upto, and including full bandwidth HD SDI.

    Just a thought.
     
  10. CDphobe

    CDphobe
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    Sounds like an interesting possibility if you can manage it Gareth, but I suspect any discussion of the results would go WAY over my head! I'm a simple vinyl man meself :rotfl:

    As to the previous kit, it was an early "high end" CD player, launched late 80s as I recall, which had both the standard transport and DAC of the era, but also had an additional (optional) box that connected to the DAC to show number of errors corrected and number of uncorrected errors, I've a sneaky feeling it was made by Cambridge or someone similar (not the current Cambridge Audio group). Hardly a highly scientific piece of test kit, but I worked at the time in a shop that had one to show how wrong the old "indestuctable" claims were for CDs and how even a thumbprint on the surface caused disk read errors. As a curious young chappy I played around checking other bits and pieces and checked different cables transport to DAC. And as you'd expect, some of the new "digital link" cables that were just being produced at huge expense were faring no better than much cheaper fare, but there were a couple of cables that really caused error rates (correctable errors accroding to the display) to rise. Could have been REALLY awful cables, but even so the results were repeatable.

    Would love to see any feedback if you manage those tests though - but layman's language please!

    Al
     
  11. BDCSTENG GARETH

    BDCSTENG GARETH
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    just to explain quickly the test I am going to (time permitting) do is about...

    look at the picture attached.

    this is a buffered view of all the 1's and 0's being inputed to the scope, overlayed, the more jitter, the more the waveform closes from left to right. The more noise on the signal, the more the waveform closes top and bottom. There will be a point of closure, from where the reconstruction of the data cannot be "guarenteed" in digital signals (different for equipment / standards...)

    I plan to just do a comparison of the same signals, but different interconnects in the way.
     

    Attached Files:

  12. rdhir

    rdhir
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    Ther are forum questions regarding cheap digital cables exhibiting poor or missing RFI shielding.
    Symptoms tend to be some electrical applicance goes on or off and sound drops for a short period. They then ask should I go optical or just get a better/proper digital cable and they have invariably plugged in any old phono/phono cable.

    My understanding of Jitter in digital systems is that is caused by power supply fluctuations causing minute delays in processing time. After all this is the principle of modern processors and battery life performance in a laptop. If the voltage is not high enough, the CPU cannot achieve the desired clock. Perhaps optical buffering is too simple to have this problem, but I was just explaining the theory.

    My understanding on the effect of poor cables is this. A poor cable does not have the correct bandwidth for the frequency of the switching of 1,0 of the supplied signal. I apologise for not knowing the correct electrical term for the cable.

    As an example, Cat 5 and Cat 5e network cables support different bandwidths, (actually 5e also uses a couple of extra conductors in the cable that are spare for 5e) and hence it can support a "bandwidth" of 1000Mbits rather 100Mbits. Now on a computer some bit streams are error corrected so that the computer realises that the recieved signal is not good.

    In the audio world I do not know enough about the protocols to say wether such error correction exists, but I don't think it always does as that's why you would hear burst of white noise as the signal degraded but it could not be detected that it had degraded.

    Hence your oscilloscope test should show that some phono/phono leads don't really support the digital signal.

    Cheers

    Rajiv
     
  13. BDCSTENG GARETH

    BDCSTENG GARETH
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    Tektronix glossary:
    The variation of a digital signal’s significant instants (such as
    transition points) from their ideal positions in time. Jitter can cause the
    recovered clock and the data to become momentarily misaligned in time.
    In some cases the data can be misinterpreted if this misalignment
    becomes too great.
     
  14. rdhir

    rdhir
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    err.. wasn't that what I just said. Or at least that's the consequence of the fluctuations in processing time as the digital data is serialised.

    Cheers

    Rajiv
     
  15. BDCSTENG GARETH

    BDCSTENG GARETH
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    I didn't contradict you, but jitter can be caused by numerous factors, one of which you have stated.

    No offence intended.

    Gareth.
     

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