Coax OR Optical Audio Output???

Discussion in 'Blu-ray & DVD Players & Recorders' started by mpicc, Apr 18, 2001.

  1. mpicc

    mpicc
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    When connecting the Audio output from your DVD player to Dolby Digital DTS receiver, is it better use the Digital Coaxial Output OR the Digital Optical Output?
     
  2. Guest

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    The neverending question return yet again!

    You could try with a search on this forum (or others) and find many results.

    But the short answer to your question is that there isnt any difference as the signals are digital transported, in theory, but many people think that coax sounds a little bit better.

    Whether it is worth buying a "quality" cable is another question. But generally the cheapest optical cable should be ok.

    Hope this is of any help.
     
  3. Ars longa, vita brevis

    Ars longa, vita brevis
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    please see general chat forum 'top25 most asked questions'
     
  4. mpicc

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    Thanks for the help....
    Sorry for posting twice

    M :)
     
  5. adamhamilton

    adamhamilton
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    Firstly, I can't find the general chat forum 'top25 most asked questions'.

    Secondly, I always assumed that optical would be better but after discussions with several specialist home theater shop managers I have been informed that coaxial is better because the optical standard was originally developed for CD players and doesn't accomodate the entire dynamic range used on DVDs.
     
  6. Reiner

    Reiner
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    Optical connections undergo additional conversion (electrical to light and back), as well the cheap cables might suffer from reflections at the connector ends introducing distortion.
    Coax is said to sound warmer but it has nothing to do with the dynamic range - IMHO.

    DD/DTS is transmitted as packets and that would explain why the difference between optical and coaxial can only be heard with CD Audio (PCM).
    In fact I have not heard anyone claiming he could hear a difference with 5.1 sound between optical or coaxial connection.

    As for the same reason it is recommended to use a "digital" (75 Ohm) cable for coaxial connections and not a standard interconnect
    though it doesn't have to cost several hundred pounds - and if you are handy with the soldering iron you can do it probably for less than what you would pay for a proper optical lead.
     
  7. bigalroz

    bigalroz
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    OK, for the final time: There is NO difference between Co-Axial or Optical digital cables the data that is passed over the cable is exactly the same regardless of whether it is light or electricity. 100011110011110011 will be sent and received over a digital connection as 100011110011110011 every single time on both cables types. The only place you need to worry about quality is in the DACs and after i.e. speaker cable, speakers, analogue interconnects etc. This applies to DVD and CD. An extremely cheap DVD/CD player will output exactly the same bit pattern as one costing £5000, this is FACT. Anyone who tries to convince you otherwise is either wrong, misinformed or lying (or trying to sell you an expensive cable :)). The only real reason to buy an expensive DVD/CD player is:

    1) Better picture quality (analogue information sent to your display)
    2) You use the analogue outputs for sound.
    3) Features.
    4) Possibly better build quality there for a longer working life for your DVD/CD.


    P.S. I am a software engineer by profession.
     
  8. Gary Palmer

    Gary Palmer
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    Bigalroz

    "An extremely cheap DVD/CD player will output exactly the same bit pattern as one costing £5000, this is FACT. Anyone who tries to convince you otherwise is either wrong, misinformed or lying"

    Then I am happy to be lying.

    The issue is not about the digital data being correct it's about timing and jitter as the samples are fed into the DAC.

    This is especially true for CD PCM data. I feed my Micromega CD and my Toshiba DVD player both via coax digital connections to my processor. So I am using the same internal DAC in the processor for both machines and the same bitstream is being output if I use the same CD in each machine.

    I should not hear ANY difference according to your theory.

    In fact the soundstage from the CD player (remember I am not using the players DAC) sounds much wider and smoother than the 'same' PCM bistream output from the DVD player using the same disc. If they really were the same I would sell the CD player and buy DVDs and CDs with the money.

    I can't comment on the optical vs coax thing as I have not tried it. I am also not sure about hearing much difference for DD & DTS as the codecs are lossy in the first place.

    BTW - I have a Degree in Electronic Engineering and I was a realtime systems software developer for several years ;)
     
  9. Guest

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    I can hear differences!

    PS: I don't have anything to do with software, hardware or earthenware, but I do have very good hearing :p
     
  10. bigalroz

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    Gary,

    Don't you just love these hot debates? :D

    As I understand it jitter can be defined as timing errors produced when creating the analog signal (that is passed to your speakers). The analog signal is created by the DACs (Digital to Analog Converter) via DSP (Digital Signal Processer) from the digital stream that is coming into your receiver. The only place I can see jitter ever being a problem is in this conversion process. The DACs using a clock to clock out the analog signal. Depending on the quality of the clock signal jitter may be produced (It is debatable whether jitter at this small a level even produces effects audable to the human ear). So the input signal will will have no effect on the sound as all timing errors are produced after the signal has arrived at your receiver.

    The sound quality is totally dependant on your DACs to produce an accurate representation of the original analog signal that was recorded.

    Buy a better receiver get a better sound regardless of the DVD player quality (as long as you're using a digital connection optical or co-axial makes no difference)

    p.s. Gary, I explained the terms DAC and DSP for any non technical readers of this thread.
     
  11. Ars longa, vita brevis

    Ars longa, vita brevis
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    RU sure i think most hardware reviewers would say bull sh*t, theory is completely different to practice i feel a meridian dvd player could somewhat whup the ass of a bush pos

    yup, just tested this upstairs with pioneer 919 and technics micro system using DAC in yamaha dspa2 and played through the dvd sounded more forceful and full.

    If a (wealthy) audiophile can spend £50 on a cd player and use it as the transport, why would he buy one @ £5000, the lot would be named as a scam.

    perhaps your theory is correct in theory (which i doubt as a more epensive laser is likely to be able to read more) perfectly a 1 ans a 1 and not a dirty 0, i don't know, but certainy not in practice.
     
  12. bigalroz

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    B*llsh*t, OK so I studied digital systems and software for 4 years getting a 1st class honours degree and then come on here to talk nonsense did I?

    C'mon guys use your brains. If a bit was read incorrectly then the error correction algorithm would be easily be able to correct it, extremely easy to do with checksums and parity bits. I work with digital data communications day in day out. Last month I was testing digital data comms to Australia over the telephone line. Data sent from our lab in Scotland is received in Australia exactly as it left the lab. Now think how many thousands of miles this data has to travel via copper, optical cable, and satellite via god nows how many switching networks and relays all within a matter of seconds. If this arrives at it's destination succesfully then how come a DVD/CD player cannot read bits from a disk, correctly pass them over a clean cable a length of a few meters at most in order for them to be processed correctly.

    A lot of people seem to think that the bits have no meaning but it does. Data messages are usually transferred in a packet which takes the form simialr to <header><data><tail> where the header contains data about the data section (called meta data)i.e. length of data, type of data etc. Then follows the actual data itself then the tail which usually contains error checking stuff like LRCs (Longitudinal Redundancy Check, Parity bits etc). Now if any of this data is incorrect then it is easy to check as the data contained in the header and tail won't match the data in the data section. If it is too badly corrupt to for any error correction to take place then you get much more obvious errors ie. skipping an jumping.

    There was an interesting thread over at nullweb page where a guy who claimed to work for Dolby writing some of the decoding software actually traced what was coming over the cable from different sound cards in his PC using different DVD software players and low and behold the data was exactly the same.

    If you think you can hear differences think about the process of testing. You listen to a few minutes of sound, change the cable to another one, listen to the same section again.

    Now this is fundamentally flawed because you are relying on your memory of the sound from the first listening. You are also likely to be listening more intently to the sound the second time as you are deliberatly listening for differences. Now the sound is likely to very complicated as you may have the score, talking, and sound effects all going on at the same time. The score itself is likely to be made up of hundreds of instruments playing at the same time. In fact I seem to remember Stuart M. Robinson stating in a thread recently that in blind testing not one person could tell any difference.


    It also doesn't help when magazines write articles on this stuff claiming to be experts when they are not (most home cinema and hifi reviewers have degrees in English not electronics or computing). People tend to believe any old rubbish if it appears in print in a supposedly reputable magazine/newspaper.

    Sorry for being long winded but believe me "bits are bits" there is no difference! If there was then the technology would not work at all!
     
  13. Gary Palmer

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    Bigalroz,

    "B*llsh*t, OK so I studied digital systems and software for 4 years getting a 1st class honours degree and then come on here to talk nonsense did I?"

    We are in awe of your vast knowledge.

    Big deal. I happen to have a 1st class degree as well. If you want to trade arrogance I did a PhD in realtime digital control systems as well. However, I am not arrogant enough to assume that I know everything just because of this fact.

    The point is this - there is plenty of evidence that jitter is a real issue - especially with PCM. Tiny timing errors cause substantial harmonic distortion. I and most people can hear a noticable difference.

    The point is that the packets of data you are talking about are NOT time critical real-time signals. As long as the bits get there uncorrupted it does not matter precisely when they get there (ever noticed that good old satellite delay on the phone ???).

    When data comes of a CD and goes to a DAC if one sample is slightly misplaced by one clock pulse guess what ? Significant harmonic distortions. The data is correct. It just got used at slightly the wrong time.

    I suggest you check out some of Paul Miller's stuff in HiFi Choice on jitter and related issues. I doubt you will be able to pick holes in his technical knowledge.

    You might like to consider whhy Tag have a proprietary clock connection between their DVD drive and their processor specifically to minimize jitter.

    BTW - in a digital control system you will find that timing errors lead to instability and are a real problem. Check out any digital control text book.
     
  14. Cliff

    Cliff
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    Coax or optical- it's the same digits. If you look at the circuit you will find that both the TOSlink and the coax out go to the same chip were the information is output. Only difference is the TOS link requires a few volts to drive the LED. Let's not get wrapped up in journalistic nonsense!
    I believe the HiFi people in the UK said that coax was better because most of the British manufacturers used coax (for CD). Where as the Japanese liked the idea of a "hi tech optical link. Actually the coax is easier as you can run long lengths of 75 ohm coax which is a lot cheaper than buying an optical cable. I use the miniture cable off the reel from Maplin. (yes, I am an electronics engineer- you can probably tell from the down to earth reply!)
    Cliff
     
  15. Gary Palmer

    Gary Palmer
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    Hi Cliff

    Thanks for getting the thread back to the original question - Coax or Optical.

    Personally I have never tried to compare them. Most people favour Coax as it is thought (I stress the word thought) to be one less conversion in the signal path. I suppose it's technically feasible that the optical conversion could introduce more problems with jitter but I've never tried to compare so I can't claim to KNOW.

    Sorry if my above response got a bit high and mighty. I get so frustrated by apparantly informed "statements" like the above one stating that the only reason for buying a better DVD or CD player to improve the sound was if you used the analogue outputs. This is just not true and there are good, well founded technical reasons for it (which do not originate from me). More importantly, most people, including myself, can hear the improvement.

    However, it may only be valid for PCM.I am not so sure about DD and DTS. Both codecs are actually quite severely compressed and I wonder if the small differences introduced by improved jitter are significant compared to the original data reduced bitstream.

    I'll climb off my soap box now and go and listen to some nice music :D
     
  16. bigalroz

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    Gary,

    Of course I don't know everything, my stating that I had a degree was not meant to indicate that, just to state that I have some experience of digital systems. My apologies if I can across as big headed, that was not my intention.

    Still don't agree though :D
     
  17. MarkB

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    Using the same CD player to output optically and coaxially into the same decoder will deliver exactly identical results. I think co-axial is better for long runs, but that's about it.
     
  18. AVMAN

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    RIGHT, LETS SORT THIS OUT. OPTICAL CABLE IS JUST A BEAM OF LIGHT CARRYING A DIGITAL 50 OHM SIGNAL. COAX IS AN ELECTRICAL CABLE WHICH CAN BE IMPROVED BY COPPER/SILVER ETC AND IS A 75 OHM SIGNAL. NOT ALL COAX CABLES ARE MEASURED AT 75 OHM ,SO CHECK OUT THE TAG MCLAREN COAX ITS MEASURED AT 75 OHM.
    WORK IT OUT COAX RULES!!!!!!!!!
     
  19. Gary Palmer

    Gary Palmer
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    Hi Bigalroz,

    You are entitled to your opinion.

    If you're ever in the Yorkshire area come and have a listen.... ;-)

    Gary
     
  20. ISCM

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    This debate should be about High Jitter v Low Jitter.
    All things being equal, PCM output using Coax and a proper 75ohm lead will out perform an Optical conection, because the conversion that takes place from electrical to optical and then back to electrical introduce more Jitter. (The human ear is very sensitive to timing errors introduced by jitter)
    DD/DTS is more robust than PCM and so the difference may not be so big.
    I had a Samsung DVD (with high Jitter) and even my wife said 'why is the music from CD's not clear. When I changed to a Pioneer 919 (with low Jitter)using the same DAC the difference was like night and day. I tried the optical conection with both players and can say that the quality was not so good, although the difference was not as great as between the Samsung and Pioneer.
    Make sure you use a proper 75ohm digital lead, as this is important. :p
     

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