Optical versus Coaxial

Discussion in 'Satellite TV, Sky TV & FreeSat' started by platty2890, Feb 5, 2009.

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  1. platty2890

    platty2890
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    I have an old thompson box and i have noticed on the new samsung,pace boxes that they now have a choice of optical or coaxial output for audio_On dvd players i have always preferred the coaxial output over the optical.Has anyone compared the 2 outputs from the new boxes.
     
  2. Uridium

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    Both digital so there is no difference. It's all just 1's and 0's ;)
     
  3. platty2890

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    I found that optical sounds thin and a coaxial a lot warmer on dvd players and the fact that coaxial connection is a lot more solid connection than the flimsy optical connection.

    I just want to know if anybody has compared them and see if they noticed any difference.
     
  4. GasDad

    GasDad
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    By what mechanism can there be a difference ? (unless they are handled by different DACS in your amp)
     
  5. D-Zyne

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    The only difference I know of is if you're running it long distances. Optical isn't good for long runs and the cable cannot handle sharp bends (small bend radius). For short runs, no difference....
     
  6. platty2890

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    Proof is in the listening not by technical specifications as any audiophile should know.You are basically saying that since its all 0s and 1s two cd players with the same spec dacs sound exactly the same they dont.

    Please i just want replies from people who have compared it not someones own thoughts or ideas.:lease:
     
  7. Hippogriff

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    OK, here goes...<pause for effect>... I've tried both cables and they sounded exactly the same... to me.

    But that's the caveat, ain't it? Subjectivity... and hearing ability of course.

    Cheers, DpM
     
  8. Trollslayer

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    Both carry the same data stream.
    Optical for longer runs avoids the risk of earth loops, coax cable is more robust.
     
  9. Andy98765

    Andy98765
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    It is 1's and 0's, an optical input is a fibre optic reciever that connects directly to were a co-ax cable would normally plug in, all it does is convert a 1's and 0's data stream into pulses of light or vice versa. The conversion has no impact on the 1's and 0's and therefore can not have an impact on the sound. It is the electronics within a DVD/CD player or AV amp that influences the sound.
    Now if you start talking analogue cables then YES, they can influence sound/video.
     
  10. Steve N

    Steve N
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    Same here.
    I went with Optical just 'cos it happened to be the last to be tried, so I just left it in.
     
  11. mudstuff

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    I haven't compared but I use a £60 qed coax from my old dvd player now that bluray uses hdmi (also qed, and my speaker cable - see a pattern ;)).

    Sound quality over the coax is great on a good movie with lots of depth and more bass than I expected now we're spoiled with lossless audio.

    Haven't used optical on it but previous experience with optical is that they are cheap and flimsy and seem to lack the range IMO so I stuck with coax.
     
  12. Bachstrad

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    Expensive digital cables ...... :rolleyes:

    ATB

    Max
     
  13. Hippogriff

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    I get most of my cables from Lindy. I like this place. I use their Premium Gold TosLink cables... not so flimsy, not so cheap either. The choice here is about build quality rather than sound quality of course.

    I like 'em. I use this cable for the three TosLink runs I have in the house, whether they be 0.5m, 1m or 20m (which one is).

    Cheers, DpM

    P.S. the only downside to TosLink, if you're an idiot - like me, is that the other night I spent about 15 minutes behind the equipment rack (quite dark behind there) trying unsuccessfully to ram the new TosLink cable into the back of my old Sony STR DB940... and it just wouldn't go in (like a drunken first date, I was huffing and puffing but no joy gaining entry) until I finally realised I'd left the little transparent rubber cap on the end of the cable... also could be like a drunken first date.
     
    Last edited: Feb 5, 2009
  14. GasDad

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    Given they carry exactly the same informatiton (they have to or they aren't working to the standard) I'm sorry but :rotfl:

    And yes I've listented to them both, and yes I'd pay a few tens of pounds for an analogue connection, but for digitial coax, over any reasonable length any old bit of wire will do. Nobody in a properly organised blind test has ever been able to differentiate between different coax cables.

    And posts like yours have to be responded to, because otherwise users of google etc may find your post and think 'hey I've got to spend 60 quid on a digital interconnect'. And frankly other people don't need to waste money - if you want to waste yours - that's up to you.
     
    Last edited: Feb 5, 2009
  15. NicolasB

    NicolasB
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    Well that, of course, is complete b*llocks - electronic detectors are far more sensitive than the human ear, and any difference that you think you can hear but which cannot be measured using instrumentation is guaranteed to exist only in your imagination.

    However, the following statement is also highly questionable:

    The difference, of course, is in the jitter. It's not just a question of whether you can distinguish between a 1 and a 0, there's also the question of exactly when each pulse reaches the DAC. Many DACs use the input signal itself to generate timing information. If the pulse arrives at the wrong time, then the DAC's output will have the correct voltage level, but at the wrong moment, which introduces distortion.

    The question of what can or cannot introduce jitter, and under exactly what circumstances it can have an effect, is a somewhat vexed one. It can definitely affect a PCM signal. I have yet to read a definitive statement as to whether it can or cannot affect an encoded audio format (such as Doly Digital). It definitely (except in purely theoretical cases) cannot affect a DAC which buffers and reclocks the signal (and thus also has virtually no effect on a DAC that uses asynchronous upsampling; but synchronous upsampling is no help).

    Some people will tell you that the quality of a coax interconnect can have an influence on jitter, because slight imperfections (such as, for example, pulses reflecting off the end of the cable, bouncing back to the source, and then reflecting again) can cause the edges of the pulses to get slightly fuzzier (so that the wave-form is less perfectly square). This means that the exact moment at which the voltage switches from high to low is less well-defined, and the DAC loses timing information. Cables that filter out high-frequency components might also cause the pulses to spread slightly and thus mess up the timing.

    One thing which could definitely produce jitter is the process of converting electrical signals to optical signals (or vice versa); so it's by no means impossible that the optical output from a digital source could be more jittery than the coax output (or that jitter is introduced to the optical input by the DAC itself). However, this is certainly not guaranteed.
     
  16. Hippogriff

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    Indeed. When I bought my new telly from Currys I asked for a discount... they wouldn't give me one. They're actually quite price competitive these days, anyway. So I sulked a little bit and the girl finally went away for a while to pretend to speak to someone (I mean, they never do speak to someone, do they?) and when she came back she said that I could have a £40 HDMI cable thrown-in.

    I looked at her, and decided to ask if it was diamond plated to which she responded in all seriousness that "no it isn't, but it is gold plated".

    I said "I'd prefer a PS3 game"... but, sadly, she could not do that for me.

    I took the cable anyway. Got it all home, plugged in the PS3 and the picture was amazing. Absolutely amazing! Wow! Those expensive digital cables really do(?) have a positive effect!

    Hahahahaha! As if.

    All that is true... apart from my realisation about digital cables. It's still plugged in though. Maybe I should buy a £5.99 HDMI cable and try to sell this £40 HDMI cable on eBay to somebody who thinks it's 'better'.

    Cheers, DpM
     
  17. GasDad

    GasDad
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    Even if that was an issue - there is no rational explanation that makes a coax without jitter sound 'warmer' or any of those other daft adjectives people give to digital cables.
     
  18. NicolasB

    NicolasB
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    There is no such thing as "a coax without jitter".

    As I've explained above, all sorts of effects in a coax cable can cause pulse edges to becomes less sharp, which produces jitter.
     
  19. Bachstrad

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    If there wasn't so much snow in Bristol you could join me at the Mall .... I'm looking for a 5Lt Mug for my tea .... I want my tea deeper, but I'm worried about keeping it warmer! :D

    ATB

    Max
     
  20. Hippogriff

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    I remember when hi-fi magazines and shops used to advise us all to expect to spend 10% to 20% of our overall budget on cables.

    Ah, the good old analogue days. Thicker wires, shielding, electromagnetic interference, RFI, insulation, metal plugs... all excellent fear vehicles for removing cash from customers... "Oh my word... you're spending £800 on your CD player and you're going to connect it to your amplifier with those little red and white phonos you got free in a packet of Cornflakes?" ...not robbery, as such, 'cos analogue did get benefits from these more expensive cables, but I'm glad those days are slowly going.

    Digital revolution onwards!

    Most of the kit you buy these days is gonna be so damn good at performing what it is intended to do, you don't really need to worry... unless your bank balance requires belittling by you buying some obscure make of product that has been hand-built by virgins using sterilised tweasers... in a vacuum. Now style and reliability... other angles.

    Cheers, DpM
     
    Last edited: Feb 5, 2009
  21. GasDad

    GasDad
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    Sorry my post was a little vague. I was just trying and failing too point out that jitter cannot cause one cable to sound 'warmer' than another. It could of course if it was severe enough cause a cable to drop bits etc., but that is not the same as these woolly statements about 'warmth' and 'colour' you sometimes hear in peoples descriptions of digital interconnects.

    Given that different levels of jitter are the only difference between say a metal coathanger and 300 quid rip off cable (assuming reasonable levels of impedence etc) - there can be no real (rather than imagined) audio difference.
     
  22. mattclarkie

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    I personally prefer coaxial to optical, I think my amp handles it better, but the difference is so minimal.



    I have Belkin Blue Series Coaxials that was about £12 for 3m, the shorter cable was more expensive :eek:.
    I also have some Extreme HD opticals and Belkin Blue Series opticals and the build quality on all is brilliant.



    For some reason I put Component instead of Coaxial.
     
    Last edited: Feb 5, 2009
  23. Martin J.

    Martin J.
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    Perhaps we should be a little more precise though... A DAC is looking for the difference between the high and low points of a waveform to represent the "1" and "0" of a digital signal. It doesn't matter if the edges of that waveform aren't square, provided the time window between the two states is within the tolerance of the DAC (most of which reclock their inputs anyway) and sample rate. The cable itself doesn't have jitter, which is a function of the DAC, it's probably best to say that it has loss, or that the signal loses integrity.
    The supposed audible differences in digital cables have never been proven by any controlled listening tests. What is more, Dolby once published an AES paper on the effects of jitter, and it was determined that huge amounts were required before its effects became audible, in order of magnitudes more than in any domestic system.
     
  24. NicolasB

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    That is not all it's looking for. It is also trying to determine timing information by looking for the leading edge of a pulse. If the pulse edge is not perfectly vertical (which it can't be unless the cable has infinite bandwidth) then where, within the finite rise-time, does the DAC decide that the edge of the pulse lies? It might (for (example) be looking for the moment when the voltage is half way between the 0 and 1 levels, and labelling that as the official pulse leading edge.

    This means that even very tiny fluctuations in the voltage (caused by, for example, interference) can have a quite measurable impact on the exact moment that the voltage passes the half-way point. It also means that a high-bandwidth cable will likely sound better than a low-bandwidth one, because the leading edges of the pulses will be closer to vertical, and so the possible error in determining the time when the voltage passes the half-way point will be that much smaller.
     
  25. NicolasB

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    Well, that depends what you mean by "warmer". I think it's quite valid to describe a sound afflicted by jitter as "cold". You might also describe it as "metallic", or "digital". :) Certainly jitter has a very profound impact on sound quality. Whether the amount of effective jitter that a cable introduces (by the mechanism of blurring the pulse edges) is enough to be audible is debatable - but it's certainly not absurd to suggest that it could be.

    You'll notice that almost no one claims that the quality of an optical interconnect has any influence on the sound, but many people claim that the quality of a coax interconnect does. That may well be significant: optical pulse edges will likely be much sharper.

    Of course, if you buy a reclocking DAC then all this ceases to matter....
     
  26. GasDad

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    But at the frequencies we are talking about, basically all cables are 'high bandwidth' over reasonable distances.
     
  27. mattclarkie

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    I've always thought that Optical signals sound Metallic, a slight reverb particularly at higher pitches..
     
  28. Andy98765

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    Leadng edges, trailing edges, now I would expect this in the telecoms industry due to the line lengths measured in Km, not in a piece of cable or fibre no longer than 1 metre, next we will be measuring the length and impact on jitter inside the Av amp or DVD players printed circuit board copper tracks which can be measured in mm. The numbers we are talking about here are minisule to have next to NO impact on a measuring device let alone the human ear which is poor at the best of times.
    All you need is a well made cable (optic or co-ax) that mates with a socket and has good mechanical build quality.
     
  29. Martin J.

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    That isn't the only way that clock information is determined, because each SP-DIF frame has a pre-amble based on three half-bits of the same value, which makes it possible to determine and construct the rate from the biphase mark code. In fact, there are many DACs that determine the clock rate based on the word clock alone and completely ignore the timing of the data, choosing to re-clock it based upon the pre-amble.

    Worth mentioning here that even with a "perfect" interface, sampling jitter can still occur, which of course is completely independent of whatever cable is used.
    I think that's really overstating the issue as far as modern DACs are concerned. The AES paper on the subject (I'll try to find the pre-print number if you'd like to download it) not only details the huge amount of jitter needed for it to become audible, but also how it effects the signal. It is said that random jitter reduces the SNR (ie increases the noise floor) and periodic jitter increases THD (by, in its extreme, introducing harmonics). Neither make the sound "warmer" or "colder".
    Supposedly the weakest link in an optical system is the quality of the transmitter and receiver circuits, and there have been a fair number of "audiophile" alternatives. ST-Glass for example, and of course Lightpipe in professional circles, which was really intended to overcome SP-DIF's design limitations on the number of channels etc.
     
  30. platty2890

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    I do apologise if my post implied spending a lot on cables as i would will probably spend(less than a fiver) to buy a good quality version of either cable.

    Sounds like it doesnt make any difference so if i do eventually get a pace or samsung box i probably use the coaxial connection as its a more solid connection.:thumbsup:
     
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