What's the difference? SPDIF/Optical/ Digital Coaxial

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Guyunique
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2006/01/18 18:10:20 (permalink)

What's the difference? SPDIF/Optical/ Digital Coaxial

Hello everyone, I recently went to BestBuy to purchase some digital audio cables.
I bought several digital coaxial cables but when I returned to the studio and opened the cables, I noticed a chart classifying the different digital audio formats. According to the chart, Optical digital cables/format are better then coaxila digital format.
Now I know spdif is Sony/Phillips digital interface. But Is this true? Infact most pro-audio has coaxial instead of Optical.
The chart rated Optical as "BEST" because the sound was travelling as light and rated coaxial as "BETTER."

Does anyone have ides on these formats? Is Optical digital format better then coaxial?

Talk to me.

Thanks, Patrick
post edited by Guyunique - 2006/01/18 18:18:58
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9 Replies Related Threads

    dcastle
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    RE: What's the difference? SPDIF/Optical/ Digital Coaxial 2006/01/18 18:23:26 (permalink)
    Is Optical digital format better then coaxial?

    The data is the same. Theoretically there shouldn't be any difference between theory and practice, but in practice there often is!

    Optical cables are non-conductive so they are immune to ground loops and they are more immune to impedance mismatched reflection.

    Optical cables have different connectors --- I don't like them because they can be pulled out way too easily.

    IMHO, good coaxial cables installed properly and not abused will be perfectly fine!

    Regards,
    David

    P.s., let the religious wars begin.

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    brendantownsend
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    RE: What's the difference? SPDIF/Optical/ Digital Coaxial 2006/01/18 18:52:37 (permalink)
    IMHO, good coaxial cables installed properly and not abused will be perfectly fine!


    Ditto !

    Optical cables can also vary in quality, and they are also susceptible to natural coupling loss at the connectors - particularly if dust gets into the receptacles. Should you need to switch out such cables regularly then dust can create a problem (hence the blanking caps for protection when not in use).

    The data format is however the same, and should anyone suggest that optical and electrical make a significant difference to reproduction quality then don't believe the commercial "jargon". It may however be more convenient to use a short optical coupling when your transmitting and receiving devices are in close proximity, and here shorter is universally better.

    My preferred approach is to use good-quality 75-Ohm coaxial cables that are not too short (e.g. >1.5m). Shorter electrical cables have been known to increase "jitter" which can impact upon signal integrity, and longer is generally regarded as better - particularly when you are using the correct coax impedance (i.e. 75-Ohms). This cable impedance is common, such as found with TV aerial downleads for example, and you can always inexpensively make these cables to length yourself to suit your layout.

    In my experience there is still considerable margin for error and impedance mismatch, but overall coax is perhaps the professionals choice


    Brendan.

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    markmann
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    RE: What's the difference? SPDIF/Optical/ Digital Coaxial 2006/01/18 23:11:59 (permalink)
    Patrick,
    I've tested digital cables extensively in my system. Here's my opinion. The best digital cable is a good AES cable. The second best is S/PDIF coaxial. The worst is optical. The best brand for AES or S/PDIF that I've been able to find is Mogami. They make specific cables for digital signals (75 ohm for S/PDIF and 110 ohms for AES). Keep these cables as short as you possibly can. IMHO Mogami beats Apogee Wyde Eye cables by far. Don't bother with the stuff from Best Buy.
    Mark
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    TheFingers
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    RE: What's the difference? SPDIF/Optical/ Digital Coaxial 2006/01/19 01:20:11 (permalink)
    My preferred approach is to use good-quality 75-Ohm coaxial cables that are not too short (e.g. >1.5m). Shorter electrical cables have been known to increase "jitter" which can impact upon signal integrity, and longer is generally regarded as better - particularly when you are using the correct coax impedance (i.e. 75-Ohms).


    This is an oversimplistic explanation of what actually goes on here, the jitter is far more likely a symptom caused by improper termination of this coax bus. Indeed, if a clock cable is long enough, resonant reflections caused by improper termination would be much lower in frequency and less likely to impart phase addition and cancellation at susceptible frequencies when mixed back with the clock signal.

    Make sure your clock chain is properly terminated.

    1973 "A" neck.

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    Guyunique
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    RE: What's the difference? SPDIF/Optical/ Digital Coaxial 2006/01/19 18:31:31 (permalink)
    Hello everyone, MarkMan you made a point but can you explain further? What's wrong with the cables sold at BestBuy?
    I'm not being defensive just want to know more. The cable that runs from my digital mixer to my Presonus Firepod is a Monster brand, it cost about $40.00 for 1m or 3ft. This is rated according to Monster as one of their best digital coaxial cable.

    But this time I went a little cheaper and bought a brand called "Acoustic Research" it's about $20.00 for 1meter/3ft.
    Now that you've said this, I want to return these cables, even though I cannot tell the audio quality difference.

    One thing I do notice about the Monster brand I previously bought is that it specifically tells you the signal direction flow.
    Which means you have to hook the input/output according to the direction flow. The Acoustic Research brand does not.


    Talk to me folks.

    Patrick
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    Tomcat
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    RE: What's the difference? SPDIF/Optical/ Digital Coaxial 2006/01/19 19:00:24 (permalink)
    Interesting discussion; however, the bottom line is that you will have to use whatever cable connects to the hardware you want to use, and, if necessary, use an adapter in the middle.

    In my case, if I want to connect the sp/dif out from my Korg D1600 HD recorder into the sp/dif input of my Presonus Firebox, I have to connect the optical out (TOSlink) into an M-audio CO2 adapter and a coax sp/dif cable from the CO2 into the Firebox.

    In other words, it's not just a simple choice of "I think I'll use optical (or coax) to connect my gear"; instead it's "I'll use whatever my hardware requires me to use".

    Tom
    post edited by Tomcat - 2006/01/20 12:33:06

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    dcastle
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    RE: What's the difference? SPDIF/Optical/ Digital Coaxial 2006/01/19 19:41:10 (permalink)
    Greetings Patrick,

    But this time I went a little cheaper and bought a brand called "Acoustic Research" it's about $20.00 for 1meter/3ft.
    Now that you've said this, I want to return these cables, even though I cannot tell the audio quality difference.

    All you need is a high-quality 75ohm coaxial cable with RCA connectors at both ends. I have reliably used $2 video cables. The frequency is only 6 MHz, which is about the same as old-fashioned composite video. I know there are going to be people claiming that they can tell the difference between s/pdif cables, but I flat out don't believe them, and I'd be happy to assist them in a true double-blind test to see if their ears are as good as their mouths ... erh fingers in this case.

    One thing I do notice about the Monster brand I previously bought is that it specifically tells you the signal direction flow.
    Which means you have to hook the input/output according to the direction flow. The Acoustic Research brand does not.

    This is pure snake oil! Well almost. It is possible to minimize the ground loop problem by connecting the shield only on the sending end, but this is very rarely necessary. Most s/pdif interfaces go through a transformer, which removes common-mode noise.

    http://www.epanorama.net/documents/audio/spdif.html
    Standard IEC958 "Digital audio interface" from EBU (European Broadcasting Union) details:

    * Audio format : linear 16 bit default, up to 24 bit expandable
    * Allowed sampling frequencies (Fs) of the audio:
    o 44.1kHz from CD
    o 48 kHz from DAT
    o 32 kHz from DSR
    * One way communication: from a transmitter to a receiver.
    * Control information:
    o V (validity) bit : indicates if audio sample is valid.
    o U (user) bit : user free coding i.e. running time song, track number.
    o C (channel status) bit : emphasis, sampling rate and copy permit.
    o P (parity) bit : error detection bit to check for good reception.
    * Coding format: biphase mark except the headers (preambles), for sync purposes.
    * Bandwidth occupation : 100kHz up to 6Mhz (no DC!)
    * Signal bitrate is 2.8Mhz (Fs=44.1kHz), 2Mhz (Fs=32kHz) and 3.1Mhz (Fs=48kHz).

    Physical connection:

    * Cable: 75ohm +/-5% (l<10m) or 75ohm +/-35% (l>10m)
    * Line driver:
    o Zout: 75ohm +/-20% (100kHz .. 6Mhz)
    o Vout: 0.4Vpp .. 0.6Vpp, <0.05Vdc (75ohm terminated)
    * Line receiver:
    o Zin: 75ohm +/-5%
    o Vin: 0.2Vpp .. 0.6Vpp

    Regards,
    David

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    brendantownsend
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    RE: What's the difference? SPDIF/Optical/ Digital Coaxial 2006/01/19 20:42:48 (permalink)
    All you need is a high-quality 75ohm coaxial cable with RCA connectors at both ends. I have reliably used $2 video cables. The frequency is only 6 MHz, which is about the same as old-fashioned composite video. I know there are going to be people claiming that they can tell the difference between s/pdif cables, but I flat out don't believe them, and I'd be happy to assist them in a true double-blind test to see if their ears are as good as their mouths.


    Ditto - and I'll lay a wager if the audiophile's game

    ANY audiophile that is!

    Brendan.
    post edited by brendantownsend - 2006/01/20 13:51:32

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    TheFingers
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    RE: What's the difference? SPDIF/Optical/ Digital Coaxial 2006/01/19 20:57:28 (permalink)
    All you need is a high-quality 75ohm coaxial cable with RCA connectors at both ends. I have reliably used $2 video cables. The frequency is only 6 MHz, which is about the same as old-fashioned composite video. I know there are going to be people claiming that they can tell the difference between s/pdif cables, but I flat out don't believe them, and I'd be happy to assist them in a true double-blind test to see if their ears are as good as their mouths ... erh fingers in this case.


    Are you making sport of me again...and what are you talking about? Nowhere prior in this post does anyone say they can hear the difference in digital cables.

    ... erh fingers in this case.


    I hope I'm overreacting here, but if no explanation is forthcoming, I believe this will warrant a complaint.

    In the meantime. IMHO, the inability to engage in a technical discussion regarding commonly accepted theory, cannot be covered up by personal attacks.
    post edited by TheFingers - 2006/01/20 00:59:12

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