[HN Gopher] Building Ultra Long Range Toslink
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Building Ultra Long Range Toslink
Author : ingve
Score : 145 points
Date : 2025-01-07 12:39 UTC (10 hours ago)
(HTM) web link (blog.benjojo.co.uk)
(TXT) w3m dump (blog.benjojo.co.uk)
| vluft wrote:
| On a related note, the excellent DIY Perks youtube channel
| recently replaced toslink leds with lasers to do a wireless
| surround system https://www.youtube.com/watch?v=1H4FuNAByUs
| actionfromafar wrote:
| Next step, point a TOSLINK laser at the Moon Retroreflectors!
| dylan604 wrote:
| There was something posted not too long ago that bounced
| radio signals off of the moon that they then turned into an
| audio filter based on their testing on what it would do to
| the signal.
| mey wrote:
| The dark side of the moon on continuous loop would be an
| interesting project.
| dylan604 wrote:
| What happens when your sub starts kicking so hard that your
| walls start to vibrate causing the line of sight to go
| intermittent?
| ragebol wrote:
| Then the audio drops out, so it's a self-correcting problem!
|
| Also, the beam is a bit divergent, even if it vibrates the
| beam could still cover the sensor.
| dylan604 wrote:
| Not necessarily. The sub is not usually attached to a wall,
| so it wouldn't self correct like you're suggesting
| chowells wrote:
| I think you missed a joke there.
|
| Loss of signal -> silence -> no vibrations -> signal
| resumption.
| dylan604 wrote:
| no, you're missing the point. the subwoofer is not
| connect to a wall that vibrates, so it wouldn't miss the
| signal. the surround speakers and possibly the front and
| surround speakers tend to be attached to a wall. The
| floor doesn't shake enough for the sub to loose alignment
| is the point.
| gorkish wrote:
| The problem with DIY perks solution is that the manchester
| clock+data encoding is an amplitude modulated thing and isnt
| really very robust to using in free space. LED bulbs, sunlight,
| or all manner of other stuff can and will fuss with it. This is
| probably why he ended up having to go with lasers instead of
| just a big IR blaster against the ceiling. If he modulated the
| OOK signal onto some kind of carrier the entire thing would be
| a lot more reliable and as a bonus could probably ditch the
| lasers. This is more or less how the infrared wireless speakers
| and headphones of yore (80's and 90's) did the job.
| Neywiny wrote:
| So the problem with his solution is that he needed a solution
| to solve a problem?
| glitchc wrote:
| Once you replace the TOSLINK transmitter with an SFP module, it's
| not the TOSLINK tx/rx that's being tested but rather the low-
| bandwidth S/PDIF protocol operating over a high bandwidth SFP
| link. So it's not really TOSLINK that's being extended but rather
| S/PDIF over optical fibre. Maybe I'm missing something....
| toast0 wrote:
| TOSLINK is S/PDIF over (usually plastic) optical fiber. S/PDIF
| over SFP is S/PDIF over optical fiber too, unless you're using
| SFP DACs.
| myself248 wrote:
| Fiber techs have "talk sets" which are just little voice
| intercoms that you plug into an unused fiber in the bundle, so
| you can yammer back and forth between manholes/closets/whatever.
| I'm not sure whether they're even digital; it's been a while
| since I played with a pair.
| dtgriscom wrote:
| https://www.amazon.com/Optical-Talkset-Duplex-Digital-Commun...
| mrguyorama wrote:
| How do you non-destructively jack into a glass fiber? Or are
| they limited to hooking into transceivers on the ends?
| toast0 wrote:
| You're probably in the manhole to work on a fiber break
| anyway...
| 0_____0 wrote:
| My guess is it's already-terminated dark fiber with an FC
| connector (no transceiver)
|
| Found an example here.
| https://www.fiberinstrumentsales.com/fis-singlemode-
| multimod...
|
| You can't really "get into" an optical fiber mid-run without
| splicing. Splicing isn't really that hard (I've done it!
| Fusion splicers are little robotic wonders. Most of the work
| is in the prep, not the splice itself.)
| myself248 wrote:
| You're correct that the talk-sets have to plug into the ends.
|
| However, there's directional indicators that just clamp onto
| the middle of a fiber. They bend it a little and sample the
| light that leaks out of the bend, without interrupting
| payload traffic. The first one I used back in the day was an
| Exfo but there are tons of 'em now.
|
| As far as I know, these are receive-only, though physics
| doesn't seem to prohibit launching light into the fiber this
| way, it would just be an extremely inefficient process.
|
| There isn't enough light leaking out to reconstruct the whole
| high-bit-rate signal (as far as I know), but there's enough
| to tell whether the light is flowing one way or the other, or
| both. And there's enough to tell whether it's modulated with
| a _low_ frequency signal -- most optical test sets can
| generate a simple "tone", typically 270 Hz, 330 Hz, 1 kHz,
| or 2 kHz, and the clamp testers can tell if and which tone is
| present.
| theandrewbailey wrote:
| > TOSLINK/SPDIF turns this into a manchester coded serial signal,
| at around 1.5Mbps that is much more resiliant to analog
| interference
|
| When I was connecting my surround sound receiver to my PC, I was
| bummed that SPDIF standard was never improved to support 5.1 or
| 7.1 uncompressed surround sound. 5.1 DTS compression is the best
| it can do (due to the 1.5 mbps bandwidth), but PC support is
| rather limited. I gave up, and I've been using it with HDMI for
| 10 years. Running it through my video card/drivers has introduced
| (bearable) complexity, but I wonder why receivers to this day
| can't connect to PCs over USB instead. (Yes, most receivers have
| USB ports, but those are for playing MP3s off a flash drive. A PC
| isn't a flash drive.)
| dylan604 wrote:
| > A PC isn't a flash drive
|
| That could be a kind of cool app that would allow you to
| present a folder on your PC as a media device. However that
| would then require a dreaded USB-A to USB-A type of cable
| <shudder>
| EvanAnderson wrote:
| Target disk mode on a lot of older Mac machines did that over
| Firewire. You could boot the machine into target disk mode
| and it would present its mass storage over Firewire. It was
| pretty cool.
| dylan604 wrote:
| But you couldn't use the machine at the same time. This
| would be like a SAMBA share, but over USB
| zokier wrote:
| You can connect two computers with usb and setup network
| between them, so you can just use smb/cifs. Microsoft has
| even handy tutorial for that:
| https://learn.microsoft.com/en-us/windows-
| hardware/design/co...
| dylan604 wrote:
| again this is not the same thing has allowing a USB cable
| to connect from a PC to another device that is expecting
| a device that would present itself as a mass storage
| device
| UniverseHacker wrote:
| I loved that feature- I could take my shitty old laptop
| into a university computer lab and boot a powerful brand
| new mac with fast internet from my hard drive- and use all
| of my software as if it was my own computer.
| akovaski wrote:
| You can do this (in Linux, at least. Mobile devices like
| Android as well.) if the USB port of the peripheral side is a
| USB OTG port. I've only seen USB OTG ports as USB-B (standard
| and micro) or USB-C.
|
| Edit: I didn't notice before, but USB OTG is on the front
| page right now https://news.ycombinator.com/item?id=42585167
| toast0 wrote:
| I think the root of the problem is lack of bidirectional
| signalling means you have to manually configure for
| capabilities on both sides (which actually already happens for
| DTS/Dolbly over SPDIF, so it wouldn't have been the end of the
| world...). Lack of bidirectional signalling also precludes
| content protection that's more effective than setting a "don't
| pirate" flag, which might be the real reason.
| jiehong wrote:
| Part of the answer is that toslink does not support DRM, while
| HDMI does.
|
| So they never was any compelling reason to improve it like
| that. They even removed toslink output from many devices
| nowadays even if they didn't have too.
| crtasm wrote:
| I'm reminded that it did offer
| https://en.wikipedia.org/wiki/Serial_Copy_Management_System
| ahofmann wrote:
| This is wonderfully useless, what a great delight to read!
| fru654 wrote:
| I wonder if something like this is possible with HDMI? Separate
| 10G SFP+ for each color channel, one more for i2c, create a
| similar style breakout PCB, maybe add an MPO or CWDM mux... Could
| be a fun project. Optical HDMI cables are expensive and most of
| the time come with a preexisting cable which is hard to route (in
| conduits) due to HDMI connector size.
| psophis wrote:
| Not HDMI, but SDI over fiber is basically this. It can be muxed
| and is used in the broadcast industry for long haul camera
| feeds.
| crote wrote:
| Such products are already commercially available [0][1]!
|
| DIYing it is probably too painful to be doable. You won't be
| able to source any kind of protocol translation chip, so you'll
| have to send it essentially raw into quad SFP+ transceivers.
| Running 4+ fibers instead of the required 2 (or even 1) is very
| expensive, and any kind of WDM immediately blows up your
| budget. Unless you're getting the stuff for free from a DC
| renovation or something, it's just not worth it.
|
| On top of that you also have to deal with designing board for
| _extremely_ fast signals, which is pretty much impossible to
| debug without spending "very nice car" amounts of money on
| tooling. People _have_ done it before, but I definitely don 't
| envy them.
|
| [0]: https://www.startech.com/en-us/audio-video-
| products/st121hd2...
|
| [1]:
| https://www.blackmagicdesign.com/products/miniconverters/tec...
| toast0 wrote:
| If you need 4x channels, it sounds like a job for QSFP? HDMI
| is already differential signalling, so you don't need to do
| that, but you might still need level shifting.
|
| Probably a box on the source end to manage DDC and strip
| HDCP.
| raron wrote:
| > You won't be able to source any kind of protocol
| translation chip
|
| I think many of those chips are simple off-the-shelf parts.
| Probably you would need special licenses only to decode HDCP.
|
| If you have an FPGA, you could even create valid Ethernet
| frames and send the data / video stream over any standard
| switch / media converter as long as you have enough bandwidth
| and no packet loss. (10G would be enough for FullHD and 25G
| for 4K if you make it a bit smarter and can strip the
| blanking interval.)
| somat wrote:
| My plan, if I ever need long haul(>3meters) video or audio
| links, is to get the signal into ethernet(or even better ip)
| and use common network equipment to transport it.
|
| The theory being ethernet is such a well developed, easy to
| source common jelly-bean part that this would trump any gains
| that specialized transports might otherwise have.
|
| But this is probably just my inner network engineer being
| disdainful over unfamiliar transport layers.
| myself248 wrote:
| Nah, this is totally the reasonable way to do it, _iff_ you
| can tolerate the compression loss or whatever. Because 4k60
| is like 12Gbps uncompressed, and even more after you cram
| ethernet headers onto everything. So most such devices
| include some compression, and the really expensive ones let
| you configure how much.
|
| Failing that, you're probably doing SDI over your own lambda.
| zokier wrote:
| That is happening in the pro world, check out e.g. SMPTE ST
| 2110.
| wolrah wrote:
| I have wondered about the same (and/or DisplayPort) but with
| QSFP optics to simplify dealing with the four channels of data.
|
| "Classic" DVI-derived HDMI would probably be trickier because
| of variable clock speeds and additional data but modern HDMI
| 2.1 is pretty similar to DisplayPort in that it uses four lanes
| at fixed rates and sends data as packets over those.
|
| I would love to be able to use standard widely available fiber
| patch cables for long distance video runs rather than needing
| proprietary cables only offered in fixed lengths and equipped
| with enormous connectors that are not friendly to conduit.
|
| Also these days data rates are getting high enough that even
| normal lengths are problematic, DisplayPort just recently
| announced that 3 meter cables will need active components for
| the full 80 gigabit per second mode, which means that a
| computer on the floor connecting to a monitor on a standing
| desk will not be guaranteed to work with passive cables. HDMI
| also recently announced version 2.2 with a bump from 48 to 96
| gigabits per second so they'll presumably be in the same boat.
| crote wrote:
| I'm surprised it works this well!
|
| A while ago I looked into this for a similar-ish hobby project,
| and the main dealbreaker seemed to be the mandatory AC coupling
| capacitors: they are intended to block DC currents, so a signal
| which is substantially slower than intended is essentially
| fighting a high-pass filter. This is also why there are special
| AV SPF transceivers: Unlike Ethernet, SDI suffers from
| "pathological patterns" consisting of extremely long runs of 1s
| or 0s, which can cause "DC wander" [0]. SDI transceivers need to
| take this (albeit extremely unlikely) possibility into account,
| or risk losing signal lock.
|
| For this reason I pretty much gave up on the idea of reliably
| going sub-100Mbps on cheap and easily available 1G / 10G SFP
| modules. Seeing it (mostly) work for TOSLINK at 3Mbps is beyond
| my wildest expectations - I bet the LVDS driver's high slew rate
| is doing quite a bit of work here too.
|
| [0]: https://www.ti.com/lit/an/snaa417/snaa417.pdf
| MrRadar wrote:
| The article mentions S/PDIF (which TOSLINK is an optical
| version of) uses Manchester code[1] which eliminates the DC
| component by ensuring every bit has at least one transistion of
| the signal between high and low.
|
| [1] https://en.wikipedia.org/wiki/Manchester_code
| teraflop wrote:
| Yup, but that only works if those transitions happen
| frequently enough compared to the time constant of the high-
| pass filter. Presumably, that's why the author found that the
| optics only worked with signals above about 150kHz.
| crote wrote:
| The problem is the speed. S/PDIF doesn't have a DC component
| at the S/PDIF bit rate, but to an SFP+ transceiver that
| S/PDIF signal is a lot closer to DC than to its expected
| signal. A single S/PDIF bit viewed as if it were a 10Gbps
| signal looks like thousands of 1s followed by thousands of
| 0s. Yes, they all balance out in the end, but you can still
| develop quite a large drift within a single sub-S/PDIF-bit
| sequence.
|
| A thought experiment to clarify it: let's say you are
| hoisting a bucket with a DC motor. You're feeding it with a
| 50Hz AC power source. It's obviously not going anywhere,
| because it's just oscillating rapidly. You'd need for the
| motor to run in a single direction for a few minutes to
| actually lift the bucket. Now drive it with a 0.0000001Hz AC
| power source (which starts at peak voltage). The motor is
| going to reverse after 58 days, but does that actually
| _matter_? For any practical purposes, how is it different
| from a DC power source?
| MrRadar wrote:
| Thanks for the explanation!
| omer9 wrote:
| Light travels 300.000km/h, not 200.000km/h. Or did I overlooked
| something?
| halestock wrote:
| It's about 200,000km/h when traveling through fiber optic
| cable.
| rayhaanj wrote:
| I think you meant kilometres per second, not per hour.
| crote wrote:
| _Very_ simplified: the speed of light isn 't constant. The
| well-known 299.792.458 m/s constant is the speed of light in
| _vacuum_ - and glass isn 't a vacuum. Light goes significantly
| slower in a lot of mediums, including glass, and it's why
| things like lenses are possible.
| somat wrote:
| It is also why high speed trading firms invest in microwave
| radio links the speed of light through air is enough faster
| enough than the speed of light through glass that they feel
| this gives them a trading edge.
|
| Honestly, gaming the system this hard really worries me, a
| lot of our economic ability is tied up in these trading
| system(the stock market). and I can see something going wrong
| far faster than our ability to fix it.
| formerly_proven wrote:
| Speed of light in a medium is c/index of refraction, which is
| about 1.5 for every glass and highly transparent plastic.
| PaulHoule wrote:
| I think it's amusing that optic fiber connectors have had so
| little success in the market though I have a few TOSLINK and the
| coaxial equivalent in my upstairs home theater (I have a Sony 300
| disc CD changed packed with DTS 5.1 Music Discs so I'm living the
| surround music dream) and downstairs (computer to stereo,
| computer to minidisc recorder, etc.)
|
| I recently got a cable to hook up a Meta Quest 3 to a PC for
| PCVR. My understanding is that works like a high-spec USB 3 cable
| but has an optic fiber in it for the data so it can be really
| long.
| synchrone wrote:
| I tore down oculus link cable - it's just copper internally.
|
| Also oculus works fine over the "charging" type c cable +
| type-c to type-a + a classic copper usb3.0 extender of another
| 1.8 meters.
| PaulHoule wrote:
| I use it for other things and it performs admirably. (In
| particularly my Sony camera has trouble with cheap cables) It
| is one of two "elite" USB-C cables I keep near my computer,
| the other one is the shorter cable that came with the Looking
| Glass Go.
| zokier wrote:
| You can see the fibers clearly in this teardown video:
| https://www.youtube.com/watch?v=Spa_pAn871c
| pclmulqdq wrote:
| Large-scale audio systems will often use synchronous Ethernet or
| other similar protocols instead of things like TOSLINK at this
| point.
|
| Also, a general solution to "send low-bandwidth over an SFP" is
| to use FM or phase modulation to carry the signal on top of a
| carrier wave that is fast enough for the retimers in question.
| Buffer and retimer chips will not respect amplitude in a
| modulation system, but they will largely preserve frequency and
| phase.
| iancmceachern wrote:
| Yeah, there is a whole standard for it
|
| https://en.m.wikipedia.org/wiki/Audio_over_Ethernet
|
| This is what most professional places have
| dekhn wrote:
| I had a dream many years ago where I could connect all my
| house devices; all the TVs, stereos, etc, all to one ether
| network (ideally the same physical network as my switched
| Internet ports) and send AV from any source to any dest
| without having to worry that much about formats or bandwidth
| limits.
|
| It never really happened and each company came up with their
| own bespoke solution, seemingly with "mobile phone-first"
| philosophy.
| rdtsc wrote:
| Indeed. I worked with CobraNet for some years. I kind like
| their isochronous protocol. But being a layer 2 protocol I
| believe it's outdated at this point.
|
| Also greetings, again (I believe?) from a fellow assembly
| username HNer!
| khaki54 wrote:
| I love when people do random stuff like this. I couldn't even
| suss out his reasoning for taking this project on. Normally there
| is at least a notional but absurd use case. Cool project though,
| and I'm sure he had fun.
| brudgers wrote:
| Recently, I described Toslink in an internet conversation...the
| other person expected it to be like USB. It is pretty amazing how
| old this technology is and how little anyone complains about it.
|
| There just aren't Toslink horror stories floating around the
| popular internet (SPDIF is another WTF-a-75O-RCA-cable? story).
| Toslink is a technology that just works (and the normal limit is
| a generous 10m)
| blt wrote:
| TOSLink was kind of a silly idea because digital electrical
| signals would also prevent ground loops. The key is digital vs.
| analog, not optical vs. electrical.
| ielillo wrote:
| Ground loops comes from the ground mismatch between two
| electrically connected devices. When you use an optical link,
| you isolate those two devices since there is no common ground
| and the hum goes away. Same if connect a battery device to a
| grounded device.
| exabrial wrote:
| Laugh, but this probably does have some real world applications
| for Live Audio.
|
| Digital Live audio mixing is taking over, but it suffers one flaw
| compared to analog: Latency. Humans can adjust pretty easily to
| performing an action and hearing a delayed response (that's
| pretty natural in our daily lives, basically think of it as
| echolocation). This is sort of like standing farther from a
| guitar amplifier (sound travels roughly 1 ms per foot). However,
| singers have it the worst: there is 0 latency from their voice to
| the ear canal, so monitor systems try to use analog as much as
| possible.
|
| For digital audio links, every time you join then end-to-end or
| decode them, you get a bit of latency added.
|
| There are a few audio interconnects that run on Ethernet's OSI
| Layer 0 (physical medium)
|
| * AES50 is standardized, basically you can think of it as the
| 100Base-T of digital live audio. It's synchronously clocked with
| a predictable latency; with roughly ~62us per link. Pretty nice.
| Cat5e cables are dirt cheap and musicians are destructive as
| feral cats, so it it's a pretty good solution. Max length is
| 100meters.
|
| * AudioDante is also popular but actually relies on IP Layer 3,
| so latency is variable. Typical values are 1ms - 10ms. Max length
| is pretty much unlimited, with a lot of asterisks.
|
| FTA: 11us is _unbelievably good_ digital latency, but with near
| unlimited length is actually a pretty good value proposition for
| Live Audio. There may be a niche demand for a product like this:
| slap in some SFP adapters, transmit a channel of digital audio
| over whatever medium you like.
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(page generated 2025-01-07 23:00 UTC)