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Can optical cable carry 192/24?

Discussion in 'Audio Hardware' started by zonka, Mar 15, 2018.

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  1. zonka

    zonka Forum Resident Thread Starter

    Location:
    Peoria, AZ USA
    Is this a situation where some optical cables can carry 192/24 and some cant?
    Here's why I ask: In jriver when I choose my Nucs realtek hd sound card I notice the output is 192/32 - but I don't have a cable connected so i don't hear anything, but I can see it is playing.
    But when I plug an optical cable in I can only get 96/24.
    Seems weird but it seems like it is a limitation of the cable itself.
     
  2. PhilBiker

    PhilBiker sh.tv member number 666

    Location:
    Northern VA, USA
    I think it's a limitation of the format. I looked up the wiki TOSLINK - Wikipedia but it didn't tell me.
     
  3. Sevoflurane

    Sevoflurane Forum Resident

    I don’t think all optical transmitters and receivers can work reliably up to 192/24. Most should be able to manage 96/24 and some devices will max out at 96/24.
     
  4. Just Walking

    Just Walking Forum Resident

    Location:
    Abingdon UK
  5. Melvin

    Melvin Forum Resident

    Location:
    Pennsylvania
    In my experience the cable made all the difference. 2 of my DACs (Chord Qute EX & Schiit Bifrost Multibit) pass 24/192 without issue using a Lifatec Silflex glass fiber cable. Only 24/96 with plastic fiber using the same 2 DACs.
     
  6. Just Walking

    Just Walking Forum Resident

    Location:
    Abingdon UK
    Because I try to understand the underlying technology, I have been trying to find out what the bandwidth of different constructions of optic cable make to digital audio transmission. Melvin's statement suggests that there is a real effect.

    But I have been able to find absolutely nothing hard and technical on the web. There is a lot of hyperbole, pseudo-science, and manufacturer waffle - but not a single measurement to support any claim that TOSLINK cable A is better than B.

    A multimode glass or quartz optical fibre (like high-end TOSLINK cables) should be capable of 1 to 5GHz over a 1km link, and was actually the state of the art - in the early 1970's! So the limiting factor should absolutely be the transmitter and receiver, at least 100 times slower than a 1km cable.

    The hyperbole etc says that dispersion is the key parameter, and this leads to jitter. This is measured by looking at the eye pattern or eye diagram, but absolutely no TOSLINK manufacturer shows that to support their claims. The reason is that dispersion is only relevant if you are using a laser light source - the LED's that are used in TOSLINK transmitters are wide optical bandwith, and optical dispersion has no relevance at all.

    So, what is going on? Where's the technical proof?
     
    PhilBiker likes this.
  7. zonka

    zonka Forum Resident Thread Starter

    Location:
    Peoria, AZ USA
    I may use optia if I can get it to output 192/24. The problem is mu Nuc needs a mini on one end. Do high quality adapters noticeably affect sound quality in a negative way?
     
    PhilBiker likes this.
  8. Mike-48

    Mike-48 A shadow of my former self

    Location:
    Portland, Oregon
    Some very good points raised there.

    IME, the issue involves two things. The first, and more important, is the design specs of the optical transmitter and receiver, including the optical units themselves and the surrounding circuitry. Most consumer gear I've looked at has been claimed to support up to 96/24 via Toslink. If either end is not specified to handle sample rates and depths that high, it's not going to work.

    Given two devices that support 192/24, the quality of the connection depends on the quality of the cable. Like RCA cables, some are great, some aren't. Lifatec was recommended to me years ago as a reasonably priced source for quality optical cables. I haven't used their cables (I haven't used optical connections in a very long time), so I can't speak from personal experience.
     
    PhilBiker and Rolltide like this.
  9. Rolltide

    Rolltide Forum Resident

    Location:
    Vallejo, CA
    Consider the case of HDMI cables. Any cable that claims to be HDMI 2.0 can carry 4K/HDR. But where the plot thickens is any HDMI 1.4 cable that is actually made to proper specifications should also be able to do this. So when this technology came out, people had varying results with the cables they already had on hand. Some had to buy new ones, others didn't.

    From what I've read, it's a very similar case with Toslink. Even ones with low quality parts and termination can phone it in up to 96/24, but 192/24 requires a cable that is built to a higher tolerance to meet the actual specification. Keep in mind actual glass or quartz fiber is very rare in Toslink cables because it's expensive and fragile, winding it up like the RCA cables you grew up with can break them (I did this in the late 90's, sadly). I think your average optical cable these days is cheap plastic end to end.
     
    PhilBiker likes this.
  10. Just Walking

    Just Walking Forum Resident

    Location:
    Abingdon UK
    HDMI specs cannot be mapped against TOSLINK S/PDIF. To quote the definition of HDMI2.0 from hdmi.org:

    "HDMI 2.0 specification defined a new, more efficient signaling method, for speeds above 1.4b limits (10.2Gbps), to allow higher bandwidths (up to 18Gbps) over existing High Speed HDMI Wire Cables."

    So you get four sets of 18Gbps signals in a single HDMI cable. For less than $10. Which is frankly astonishing - and is probably fuelled by production runs of tens of millions per year for each brand. And Chinese, highly automated manufacture.

    Anyhow, the point is that HDMI2.0, in rough terms is 4000 times the data rate for 192/24 audio. The comparison with a TOSLINK cable does not work is the huge difference in data rate, and comparing 18Gbps coax with optical.

    All that puts the sluggish data rate of any of the audio S/PDIF specs into perspective, whether by coax or TOSLINK.

    Anyhow, coming back to my original point - although you can easily find eye diagrams for HDMI signalling, you can find nothing similar to support optical cables for TOSLINK. Which begs the question - why would that be?
     
    PhilBiker likes this.
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