What's the bandwidth for TOSlink?

Discussion in 'Archived Threads 2001-2004' started by Vince Maskeeper, Aug 4, 2001.

  1. Vince Maskeeper

    Vince Maskeeper Producer

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    Just wondering, in data terms, how much info this can carry? I know that you can carry 8 tracks of digital audio (48k/16bit) on a single toslink cable, just wondering what the spec'd limitations are.
    -Vince
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  2. Greg Monfort

    Greg Monfort Supporting Actor

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    A good question that piqued my interest. I thought a quick search would yield the answer, but all I found was that it transmits a 660nm (nanometer) red light. This equates to a 0.000026" WL, or 521,538,461.5Hz. Not having a clue how this all works, don't know if this info is of any value.
    GM
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  3. Rick P.

    Rick P. Stunt Coordinator

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    Toslink is just a connecter for a fibre-optic cable, isn't it? The optical bandwidth is a function of the receiver and transmitter used. Consumer-based stuff peaks at about 6 MBPS so that's probably the number you're looking for, while commercial stuff can do DC to 125 MBPS or better.
    Rick
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  4. Grant B

    Grant B Producer

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    Nyquist Principle tells you
    sampling freq= 2 x Bandwidth
    so if Rick was saying it was being Sampled at 6MHz you have a BW of approx. 3MHZ
    That does not take into account oversampling
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  5. Ben Cannon

    Ben Cannon Extra

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    The theroetical bandwidth for TOSlink (and ADAT) Physical interfaces is rather high, despite two limiting factors.
    Firstly, the fibre is wide, this leads to rapid "time smear" as in a curved cable, the inside 'track' is actually marginally shorter than teh outside. a square wave coming in will round off as it exits.
    This varies with legenth and wavelength of light used.
    All the above said, the *physical* limits of TOSLink (imposed by light intensity, wavelegenth, and fibre transmission, internal refraction, and width) is quite high. in the hundreds of megabits. possibly thousands.
    The fibre transmitter andn recivers are the weak link, and usually speced only a few times higher than the datarate needed by the logical layer.
    In ADAT, that is 8-tracks of up to 24bit audio at 96khz (192k is not covered afaik) sampling.
    I would like to note that almost every recording you hear has gone through several hundred feet of ADAT aka TOSLINK cable and sounds fine.
    The logical layers are different though, and SPDIF's recovered clock is not always done properly... Nevertheless, I don't put much stock in the so called "jitter" phonomena, at least, I don't hear it.
    I have a much larger beef with AC-3 (DD) and MPEG2 lossy compression, both of which's artifacts stand out to me personally.
    Hope this helps a bit, sorry for straying from the origional topic. Let me close by saying that the inherant "bandwidth" of an optical fibre is constantly being revised upwards [​IMG]
    (max bw in theroey can be locked by the above factors, but of course the physical world always falls short. Just how short changes every day.)
    Best!
    Ben
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    Ben Cannon
    Dream With Your Eyes Wide Open, Inc.
    "Every man dies, not every man really lives" --Mel Gibson, "Braveheart"
     
  6. Grant B

    Grant B Producer

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    Ben
    Many a/v PHILES tend to look down on optical as the dirty cousin of coaxial. I have always been happy with the sound. The inherent characteristics of optics being immune to most interferences that plague copper ( And hey EMP doesnt even phase it so if your electronics don't melt, you can use your HT during the nuclear winter!), makes it perferred in my book.
    What do you think?
    ------------------
    Why?
    Why do you keep hounding me and harassing me and hounding me?
    It's not like I don't have anything better to do, you know.
    It's not like the Phantom Cruiser is going to wax itself.
    It's not like last night's burrito stain will just up and remove itself from my cape.
    I am a superhero!
    A very very busy superhero! Who does...things!
    Now get out of here before I tell your mother.
    AND DON'T TRAMPLE MY BEGONIAS!
    -Space Ghost..
     
  7. Ben Cannon

    Ben Cannon Extra

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    Hi Grant, I consider myself an "a/v phile" for sure, I actually make my living from it [​IMG]
    I've never been less than happy with toslink as a digital signal trasnfer medium, sounds the same as coax or AT&T ST optical to me.
    There really is no reason that digital signal transmission should make the slightest difference in end analouge sound quality, unless data loss or extreme clock jitter occur.
    The time domain issue is the big one over TOSlink, but in my personal subjective opinion, it's bunk [​IMG]
    Either one will sound and perform great, with the added advantage of optical media totally isolating the transport from the DACs at least.
    PS: I'm new to the Fourm, SF is pretty close, I'm about 45miles north, cool [​IMG]
    Best!
    Ben.
    ------------------
    [​IMG]
    Ben Cannon
    Dream With Your Eyes Wide Open, Inc.
    "Every man dies, not every man really lives" --Mel Gibson, "Braveheart"
     
  8. Grant B

    Grant B Producer

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    Ben
    Thanks for the reply
    I feel the same way about the two. HT is a very subjective hobby. Even though I don't make a living off it, I am an electrical engineer so generally I try to figure out why something is good/bad.
    I've always said they don't pay engineers enough to be a 'phile' but it's always been my hobby.
    I've been remodeling (more like rebuilding ) my flat in the Haight (1896 Victorian) myself and thought it would be a good time to build my 'dream system'. Pretty much there...in the process of hooking up the surround in the kitchen and Bedroom which are completely independent of the main but use the same sources.
    I've heard many state coax is better but never a reason behind it.In optics, I've only delt with Dual Ring FDDIs which can transmit 100MBPS but I have no Idea if that standard has anything in common with toslink.
    Welcome to the Forum!
    There a lot of knowledgable people here who tend to give better answers than customer service techs.
    I know Petaluma well, my wife is from there and most of her family lives there....
    What related job do you have? (Always need a good excuse to sneek away from the mother in law!!)
    Grant
    ------------------
    Why?
    Why do you keep hounding me and harassing me and hounding me?
    It's not like I don't have anything better to do, you know.
    It's not like the Phantom Cruiser is going to wax itself.
    It's not like last night's burrito stain will just up and remove itself from my cape.
    I am a superhero!
    A very very busy superhero! Who does...things!
    Now get out of here before I tell your mother.
    AND DON'T TRAMPLE MY BEGONIAS!
    -Space Ghost..
     
  9. Ben Cannon

    Ben Cannon Extra

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    Hi Grant!!
    I'm actually in buisness for myself as a visual effects artist. Haven't done anything really impressive yet (mostly television and some Music Video work, my goal is to work on feature film. no I didn't work on 5th element [​IMG] I end up doing a fair bit of audio work as well, pics in my sig are my home/'office' heh. It's 6-track full bandwidth and I'm actually fairly happy with how it sounds (that's the audiophile curse, we're NEVER happy!! ! [​IMG]
    There is a reason for considering toslink not a great interface, that's got more to do with the quality of the reciver and transmitter chipsets and their introduced word clock jitter, but I've seen few reliable measurments, and sonically, I cannot hear it. I do hear amps and to an extent (not a great one, my line analouge cables are just monster 400 or equivlent) in cables too. And I even think LPs sound 'better' to my ears (or rather, I acknolege that I actually like their distortions sometimes [​IMG]
    I happen to have an FDDI network here (though it''s a SAS switched and dual-ring sort of hybrid [​IMG] It's great, I get nearly 'wire' speed on all the silicon graphics boxes, wheras with 100meg ethernet I rarely see over 70mbits in real life. I'm begining to move the faster machines to fibre channel, but expense forces me to buy gear used, and at that, only when I can find a deal [​IMG]
    Oh, almost forgot, FDDI (and almost all computer fiber optical media) is 50/62.5micron fibres, essentially the same as "AT&T glass" interfaces for audio gear. not similar to toslink which uses I belive .75mm fibers, which are *much* larger. 50/62.5micron is about half as thick as a human hair, and thus, can sustain well over tens of gigabits/second. single wavelegenth. maybe much more.
    Anyway, I'm a bit of an engineer (withought the formal schooling) myself, and I go as much by feel as by calculation, but I find the two have a synergey that is what I strive for. Hrm, that doesn't make a good deal of sense, what I'm trying to say is that by 'seat of the pants' engineering, and listening, toslink has been perfectly audiophile quality signal transmission by me.
    Best!
    Ben.
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    [​IMG]
    Ben Cannon
    Dream With Your Eyes Wide Open, Inc.
    "Every man dies, not every man really lives" --Mel Gibson, "Braveheart"
     
  10. Vince Maskeeper

    Vince Maskeeper Producer

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    Ben,
    Thanks for the post and the hard(er) data numbers in regard to the interface itself. Appreciated!
    One question:
    quote: I would like to note that almost every recording you hear has gone through several hundred feet of ADAT aka TOSLINK cable and sounds fine.[/quote]
    How do you figure? I've done almost 60 albums at this point- and have used very very little optical interfacing for ADAT. In the big money recording world, most records (especially rock) are done on Analog 24 track machines. I would say that the number of recordings run through "adat toslink" would be less that 5%, and even those- I doubt many have gone through "hundreds of feet".
    Just curious about if I misunderstood what you were saying here.
    ------------------
    http://www.musicianassist.com
    AIM: VinceMaskeeper
    Interested in moving into FRONT PROJECTION with huge 6-10 foot widescreen? Buy my whole HDTV-ready CRT based front projection system delivered, cheap! Click here
    [Edited last by Vince Maskeeper on August 11, 2001 at 08:17 PM]
     
  11. Ben Cannon

    Ben Cannon Extra

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    Hi Vince, I will admit I was speaking more of movie soundtracks than 2-channel stereo audio CD music recordings. Most film scores end up on a Tascam DA-88 tape at a later stage in their life (think of this is a mini ADAT that uses 8mm tapes instead of svhs media) Interface of choice is ADAT.
    I have less expierence in the music recording field, though I have done some work there. Everything is going 24-48-96+ track on computers now, which in my opinion is a very good thing. However I do see ADATs used quite a lot later in the mixing process, most often if two studios are working together on a project. Ie, record on 24track, mix down to vocals, backup vocal, drums, guitar, bass, etc, etc. then it's sent off to another studio.
    (I'm using "adat" and "da-88' interchangably now, as in this thread we're talking about ogical interface media not so much as actual physical tape size [​IMG]
    Again, this is just my limited expierence, but I'd say around 75% of all *audio* projects I've been involved with spent time on an adat/da-88, nearly 100% for film.
    I'd like to hear more about your pipeline, more and more we're just yanking scsi drives out of hot-swap canisters with ProTools 24track on them.
    Best!
    Ben.
    ------------------
    [​IMG]
    Ben Cannon
    Dream With Your Eyes Wide Open, Inc.
    "Every man dies, not every man really lives" --Mel Gibson, "Braveheart"
     

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