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Thread: coax vs. fiber

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    coax vs. fiber

    Well even though i am fairly new to all of this i have a question on what seems to be a much debated topic of coax digital and fiber optic audio. just looking for your opinions and maybe reasons why. Just looking to further my knowledge of ever expanding (but currently small) knowledge of ht. Thanks so much!

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    New too

    I have looked over the pros and cons of both coax and fiber. Nothing I ever read or heard proved anything one way or the other.
    I decided to go the toslink route. I know I could have done it cheaper with coax, but I was only running about 2 feet and the difference wasn't that big of deal. If I had to make a longer run to my equipment than I would have went with coax.
    When I bought my new receiver the salesman recommended toslink and gave me a good deal.
    Oh yeah, the other reason is that my dvd player has optical only.
    Last edited by Evan; 02-11-2004 at 03:16 PM.

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    Quote Originally Posted by cashlz
    Well even though i am fairly new to all of this i have a question on what seems to be a much debated topic of coax digital and fiber optic audio. just looking for your opinions and maybe reasons why. Just looking to further my knowledge of ever expanding (but currently small) knowledge of ht. Thanks so much!

    They both send digital signals. Nothing too complicated about that especially for short runs.
    mtrycrafts

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    Forum Regular sofsoldier's Avatar
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    Both coax and fiber transmits digital data. There is no way a cable can possibly affect a digital stream unless its broken! There are some important differences between coax and fiber. While both serve their pupose, coax is better than fiber in a number of ways: first of all, a fiber optic is easy to damage - especially if its made of glass. The Toslink connectors leave much to be desired as well. While they can remain in position, it is easy th pull the connection loose from the component. It is also argued that the "cheaper" fiber cables have poor mounting of the adapter resulting in signal loss. I have not seen any evidence of this.

    Coax on the other hand is as durable as any interconnect, and can be relatively cheap. For example, you can use a cheap video cable - or even a coat hangar to connect your digital device. There is a link that demonstrates the coat hangar, I'm sure someone here has that link.

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    Why coax; why optical

    It's well known that either will do the job perfectly. So you might ask why TOSlink is used at all, since it's quite a bit more expensive. What was the purpose of introducing it in the first place.

    There appears to be exactly one advantage to optical connection: galvanic isolation. If you can think of another one, please let me know.
    Norm Strong [normanstrong@comcast.net]

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    Forum Regular sofsoldier's Avatar
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    Quote Originally Posted by Norm Strong
    It's well known that either will do the job perfectly. So you might ask why TOSlink is used at all, since it's quite a bit more expensive. What was the purpose of introducing it in the first place.

    There appears to be exactly one advantage to optical connection: galvanic isolation. If you can think of another one, please let me know.
    I am not sure how galvanic isolation effects an optical transmission. Galvanic isolation is used to secure ground loops for antenae and provide electrical isolation by separating input and output signals. But I do have an idea to what you are referring: you are suggesting that there is a pocket of air between the input and output of the LED's transmitting the digital information. No physical connection - not inherent problems of resistance. But unlike electrical signals, optical signals do not suffer any resistance (that is, any measured resistance that is possible by transversing different refactive media). Propagation delay from such refractive error would be microscopic - escpecially when travelling through a 1 meter fiber.

    As far as the TOSlink, I cannot understand why such a standard was adopted since spring loaded fiber optic connectors have been used in telecommunications for some time.

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    I have listened to both and can not hear a audible difference. However it would seem to me the Coax could have the edge. Toslink takes and electric signal from the source end and converts it to light. The light has to be converted back to and electrical signal so the preamp can use it. These conversions are skiped with Coax. However I would bet we got stuck with both due to a large pissing match between sony\philips and Toshiba.

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    That is true. There must be some type of conversion occuring with the fiber and the red LED, although I have no clue as to what. But you hit the nail on the head: you confess to not hearing a difference and I certainly agree with you.

    We certianly do get stuck with a format because of "pissing contests" don't we!

    I suppose one other advantage to having coax and fiber is the availablity of connectors on the receiver/processor. If the coax has been reserved for a DVD player and the only other available connector is a TOSlink, then another digital component can be added. With my Yamaha receiver, I only have 1 coax input; however, I have 4 TOSlink inouts that are available for satellite, DVD, cable box (if it comes with TOSlink) or some other digital source.

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    optical cables have virtually no outside interference from EMI/EMR (of whatever those are exactly) because it is is transfered as light... i've found actually more people supporting coax then optical saying there is less digital harshness in the highs, but with my optical cable i dont notice much unless i turn it loud, but this could very well be my amp, dvd player, speaker cable.. so in the long run i say optical would be what id suggest to people.

    sofsoldier,
    i just read something in a business magazine that Verizon was going to spend some billions of dollars converting to optical cables for all communication transfer.. makes sense doesnt it?

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    Quote Originally Posted by sofsoldier
    I suppose one other advantage to having coax and fiber is the availablity of connectors on the receiver/processor. If the coax has been reserved for a DVD player and the only other available connector is a TOSlink, then another digital component can be added. .

    That is about the real question one needs to ask, what I have not used yet
    mtrycrafts

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    Quote Originally Posted by Just1n20
    i just read something in a business magazine that Verizon was going to spend some billions of dollars converting to optical cables for all communication transfer.. makes sense doesnt it?
    Did you read far enough to find out why? If nit, I'll tell you. Fibre does offer a wider bandwidth so they can carry more "channels" and yes, for great distances it is more prone to resist electrical interference.

    Now, do these factors affect it's performance in a home environment? As much as we need the pressure shielding of a submarine in order to paddle a canoe on the river.

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    i was only pointing out a small article i read. i dont know exactly what is being changed to fiber optics.. it just said Verizon was investing fiber optics is their communications. im not saying that because verizon is using fiber optic that im going to for my home theater. and yes i have heard that over long runs there can be transfer issues like that, but i'm saying for home theater it shouldnt have any problems since most people have 1-2 meter interconnects from dvd to processor. i'm not telling anyone to go either way, but they both have their pros and cons. i have optical and like it, but i haven't heard my system with digital coax, i am willing to try and see if i can hear a different through my not-so-revealing low-fi system. just putting my 2 cents in.

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    Forum Regular Monstrous Mike's Avatar
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    Quote Originally Posted by sofsoldier
    Both coax and fiber transmits digital data. There is no way a cable can possibly affect a digital stream unless its broken! .
    That's not quite true. There are two things that can happen to a digital signal while it is being transmitted through a cable whether it is coax or fibre optical.

    First, there is the introduction of bit errors. It is always due to the signal being degraded somehow. This can happen if the cable is too long for example and the overall capacitance is very high. As well, outside interference can get into a cable and degrade the signal. The 3 mHz S/PDIF signal can handle a certain amount of bit errors due to error correction coding but eventually you will begin hearing clicks and popouts followed by dropouts and then silence.

    Second, there is the issue of jitter which is a time shift of the digital bits. If we take a digital coax cable, all impedences should be 75 ohms. The input and output impedences should be fairly close to this and this is why you should use a 75 ohm cable, like a video cable. Since the impedences never match exactly (and the connectors are rarely even close to 75 ohms), there will be internal reflections within the cable. This introduces jitter to the signal.

    Now having said all that, internal cable reflections do not matter for cables which are shorter than a quarter wavelength. In the case of the S/PDIF signal, this is about 80 feet. So in reality, it is very unlikely that even the cheapest of home digital audio cables (assuming lengths of say under 12 feet) will contain internal cable reflections which will cause any significant jitter. And on top of that, the jitter added would need to be audible to be a problem. And the signal losses due to capacitance or RFI in a coax cable are simply not large enough in regular cable lengths to be any problem.

    Quote Originally Posted by sofsoldier
    As far as the TOSlink, I cannot understand why such a standard was adopted since spring loaded fiber optic connectors have been used in telecommunications for some time.
    TOSLink was invented by Toshiba, one of the very early digital audio research companies. There idea was to use the technology of current fibre optics and adapt it for consumer products. The cost of using "real" fibre optics would have been too great so they invented a cheaper way of connecting a plastic fibre cable to a plastic connector. This reduced the price greatly and carried the signal correctly. I remember that there is about a 25 foot maximum distance for this type of connection. Another advantage is that it can use cheap plastic cabling instead of glass and is also a lot thicker which makes it more robust.

    I personally believe that TOSlink is totally unnecessary and should just go away so we don't have processors with X digital coax inputs and Y TOSlink inputs.

    Assuming the average Joe has his digital source fairly close to his amp and is using basic cable that is not damaged, I do not believe there is one iota of difference between the two. I have heard all the technical arguements surrounding this and I am quite capable of evaluating them but I have yet to see anything that would convince me otherwise.
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    Fiber Optic cable use in telecommunications is not a new thing. The amount of data that can be transfered through a fiber optic is far greater than cable. It is also very expensive. It is no surpize that Verizon would would lay fiber optic to support their infrastructure. Its simply a matter of bandwidth. More users = more required bandwidth.

    For home audio, there is no need to support such bandwidth simply because there is no comparison between watching Pirates of the Caribbean and makeing supporting 500,000 long distance phone calls at the same time.

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    right the toslink is made from polished plastic,while real fibre optics are glass making it very expensive. coax is better in the sens if you must bend you cables more to reach the destination coax is much more resilient to breakage than the plastic toslink, as well I find the optic connectors quite flimsy while the coax is a much tighter connection...and if you are real anal you can easily clean coax connector tips !! buy both try them out and return the one you dont want !!

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