TOSLINK: That one consumer fiber optic standard

Our modern world essentially runs on fiber optic communication technology. On our increasingly connected planet, nearly everything we do from making a phone call, to checking our bank account balance, to yelling at computers to tell them to turn the lights off, to watching this very video almost certainly relied, at some point, on turning your voice, or input, or the data making this image into incredibly brief, incredibly fast pulses of light, firing that light with *A LASER* down a glass pipe, and counting the pulses on the other end. And probably doing that a whole bunch of times over potentially thousands of kilometers, nearly instantaneously. And yet, in the consumer space, fiber optics are almost nowhere to be found. We send digital video data over these complicated cables with upwards of a dozen little strands of copper inside them. Networking equipment in homes and businesses still uses Ethernet, twisted pairs of copper wire that need to be made more precisely with higher tolerances each time we want to push the speed up another order of magnitude. Really, we just haven’t seemed to find a place for fiber optics aside from piping the internet into your home or business, and even then that’s not exactly common. Except there was that one time Toshiba decided to connect CD players to amplifiers with fiber optics in 1983. Yes, although fiber optics may seem like the upper echelon of communications technology (and in fact kinda are) there has been one consumer-grade fiber optic standard floating around since the early ‘80s. That would be TOSLINK, which is a shortening of Toshiba Link. In this video, we’re going to learn a little bit about this surprisingly old optical standard. Ahh, the compact disc. What a beautifully engineered medium for storing uncompressed digital sound. As you likely know, these things store data in millions of little pits and lands, and when you shine a focused laser on those bumpy bits, the varying depth causes destructive interference and results in a reflected beam that flashes light and dark, representing ones and zeroes. Note that a pit doesn’t mean 1 and a land means 0, rather the transition from pit to land OR land to pit means 1, and a period of no change means 0. A CD player has to do a fair bit of processing before it can turn that raw data stream into sound. First it has to translate the eight-to-fourteen modulation of the pits and lands to reveal 8 bit words, then it has to parse the various signalling within that datastream for things like track and time markers, and finally it has to work through the cross-interleaved Reed-Solomon coding to actually get the individual samples that make up digital sound. Once we’re at that step, we can send those decoded samples to a DAC in order to be turned into electrical impulses that will drive headphones or loudspeakers to impart mechanical impulses into the air that we hear as sound. If you’d like to learn more about the compact disc and how digital sound works, you can check out these previous videos of mine. Now without a DAC, we can’t turn those samples into sound. Since that’s the primary goal of a CD player, the CD player itself contains a DAC, and generates a line level analog audio signal to be sent to an amplifier over garden variety RCA cables. And for almost all intents and purposes, this is perfectly fine. Unless you cross the line into audiophile territory, you are probably delighted by the sound coming from these two little jacks. And so, for most of us, that’s the end of the story. But the act of playing a CD is the very last step in the life cycle of producing a sound recording on compact disc. In the studio, digital tape machines are creating digital recordings from microphones or other analog sources, and various editing equipment needs to access those recordings to be manipulated and eventually mastered into a compact disc. All of this is different today but just pretend like it’s 1985, OK, everyone’s doing it anyway. Knowing that there’d need to be some standard way to move digital audio streams around, Sony and Philips (the co-creators of the Compact Disc standard) developed S/PDIF, which is often pronounced “spidiff” because, let’s face it, that’s more fun. S/PDIF stands for Sony/Philips Digital Interconnect Format, or you might also see Sony/Philips Digital InterFace. When Sony and Philips hammered out the details on S/PDIF, they were using standard coaxial audio cables like these to send the digital data over garden variety copper wires. And that worked fine! No one was complaining. But then, Toshiba got into the CD player business, and they wanted to be able to send the raw digital sound data recovered from the CD separately to an amplifier, letting the amplifier’s built-in DAC do the digital to analog conversion, potentially reducing noise and interference. So they did. But, someone at Toshiba was apparently dissatisfied with the ordinary nature of RCA cables. [in a very over-the-top fashion] Pfft, it’s the future! We’re using lasers to read sound from these miraculously small polycarbonate discs, and YOU expect US to convey the data they contain using WIRES? What kind of technologically regressive firm do you think this is? We are TOSHIBA! We MAKE the future! And so they did. And really, what they did isn’t all that remarkable. See, sending S/PDIF signals over copper wire simply involved having a voltage repeatedly switch from high to low. S/PDIF uses biphase mark code, also known as Differential Manchester encoding, to make the signal’s clock part of the datastream itself, but now we’re getting into specifics that don’t really matter because of this fun little truth nugget; TOSLINK transmits the same exact S/PDIF signals. Yep. TOSLINK is nothing more than a fancier way to send a S/PDIF datastream to another device. Rather than using a wire and pulsing a voltage through it, TOSLINK uses optical fiber and a pulsing light. Of course, the sending device had to run a pulsing voltage through an LED to create that pulsing light, and then again the receiving end has to use a photodiode to turn that pulsing light into a pulsing voltage, so when we get right down to it is there really a difference at all? Well, yes, but, kinda, no... And also, it’s complicated. Firstly, I don’t want to sound overly harsh here towards TOSLINK. Sending a signal through optical fiber is not only objectively cooler, but does have some advantages. Though even that’s debatable. And secondly, while TOSLINK is indeed a fiber optic communication standard, it is in no way comparable to the fiber optic networking equipment that makes up the backbone of the internet. So while TOSLINK may not have much to brag about compared to a simple coaxial S/PDIF connection this isn’t to say fiber optics aren’t important. But back to TOSLINK. One of the stranger things about it is that its history seems almost entirely unknown. I’ve been looking for some sort of patent related to it but haven’t had any luck, and even if Toshiba did patent it, it looks like they just let it out into the wild. It was fairly common on high-end CD players by the late 1980’s, and in 1987 it was referred to as an ad hoc standard by Digital Audio and Compact Disc Review. So it looks like, though Toshiba may have created it (and they appear to have the trademark on the word TOSLINK), they let pretty much anyone who wanted to use it, use it. It just sorta happened. Indeed, the TOSLINK connector and cable specifications were adopted by the Electronic Industries Association of Japan as EIAJ RC-5720 The physical bits of the TOSLINK standard are actually pretty darn simple. Take a look at an optical audio out port and you’ll see it glows with the red light of an LED. Some people think TOSLINK uses lasers, but it’s just an LED, it’s much cheaper and works fine. Taking a look inside the device reveals that, well, there’s not a lot going on behind the scenes either. It’s just a molded bit of plastic to hold onto the connector and align the tip of the cable with the LED. The cable itself isn’t really special, either. While some high-quality cables will use bundles of very thin glass strands, many are simple 1mm plastic fibers that run from one end to the other. Pretty much just a strand of fishing line. You can see that the cable will pass light through it no matter how it loops around, though if you introduce an extreme kink, you can damage the cable. With it plugged into the back of this CD player, you can see that now the other end glows, ready to pump that pulsing light into another device. On the back of an A/V receiver or other sort of amplifier, you’ll see some other TOSLINK connections though these don’t glow. Well, some of them might if it’s also got a return out for something like a digital audio recorder or MiniDisc player or whatever, but if it’s the receiving end, it’s as dark as the future of Windows phone. Inside is a photodiode which will produce a voltage when it sees light, and thus will be able to reproduce the pattern of light pulses it receives as a pattern of voltage pulses to be processed, interpreted by a DAC and finally turned into sound. It wasn’t just CD players that used TOSLINK. Wait. I already mentioned MiniDisc. Pretend I didn’t. Rewrites are hard. As more digital formats appeared on the scene, like Digital Audio Tape in 1987, it was common to see TOSLINK inputs and outputs on mid-to-high-end equipment. Fun fact! The advent of consumer digital recording really freaked out the recording industry, as now it was possible to create bit-for-bit perfect copies of a CD onto a digital audio tape cartridge. While TOSLINK wasn’t the only way to accomplish this, it was pretty widely supported by then and we may have this little cable to at least partially thank for the Audio Home Recording Act of 1992, the later Digital Millennium Copyright Act, and the subsequent DRM schemes that would be cooked up in the decades to come. [a large crowd chants in unison] Thanks, Toshiba! One of the more interesting things I ran across was a seemingly needless design detail that hints at a never-realized upgrade to TOSLINK. See, the connector itself is keyed, meaning it can only be inserted with one orientation. This isn’t necessary given that the optical fiber itself is centered, and there’s only one of them. I honestly never even thought about this. If, however, there were two fibers in the same cable, say one for transmitting data and another for receiving, there would need to be a way to ensure the fibers in this two-way cable are correctly aligned with the connector. It’s possible that the TOSLINK connector was keyed for just such a cable design, though this never came to fruition. Cool. So TOSLINK is a simple way to turn S/PDIF into light, push it through a pipe, and then turn light back into S/PDIF. But, um, why? Well, here’s where things start to seem a little superfluous. One of the key advantages of using an optical fiber to send data is that it’s not subject to electromagnetic interference. Normal audio cables like these can pick up humming or whining or any other sort of noise because they act like antennae. But… if we’re in the digital realm, what difference does that make? Sure, a coaxial cable carrying a S/PDIF signal can pick up noise, but unless that noise gets so phenomenally bad that it somehow overpowers the very powerful and not-at-all ambiguous high-low-high-low pattern the cable carries, it doesn’t matter. Analog noise in a digital signal doesn’t come out in the processed result. This has always seemed more than a little weird to me. TOSLINK’s signature advantage, that it’s immune to electromagnetic interference, would only really be a selling point if it were transmitting analog signals. But it isn’t. For the most part, either a digital signal gets through, or it doesn’t. Until the signal gets so bad that the receiver can’t piece it together correctly, it will sound exactly the same. And once problems do show up, it’s gonna get glitchy [audio defects begin to appear] or the signal will just drop out. It’s not gonna sound worse. It won’t sound right at all. So choosing TOSLINK over coaxial because it is impervious to RF interference or other electrical noise is, well, I’d argue rather uninformed. Your amplifier’s circuitry doesn’t care how it’s getting that data. And once it gets to the DAC, we’re well past the point where cables could make a difference. Now it can be argued that having your audio devices entirely electrically isolated from one another could be advantageous because it prevents freak occurrences like a huge electrical spike through your RCA jacks cooking a chip on your amp or something really unlikely like that, though if you’re really worried about electrical isolation for sound quality purposes, good luck avoiding the building’s electrical wiring they’re eventually gonna share. And then, well, TOSLINK actually has a lot of disadvantages. The most significant practical issue is that the longer the cable gets, the harder it is for light to reach the other end. Remember, this is largely a consumer standard, so even the most premium cables aren’t anything near optically pure and the longer they get, the more they reduce the amount of light that gets through. Add to that the fact that it’s only got a weedy little LED lighting the whole thing up, and you get a maximum cable length of 5 meters. In practice this can be and is regularly exceeded, especially with the brighter LEDs and with more sensitive photodiodes of more modern equipment, but with a coaxial cable you can go a lot farther before issues crop up. Now I don’t want to get too far into comparing TOSLINK to a coaxial S/PDIF connection, because that means getting into incredibly nitpicky details like clock jitter that you shouldn’t even look up because trust me it will just make you question your sanity. So instead, let’s talk about Mini-TOSLINK! Since the only part that actually interfaces with the LED and photodiode is this little nib, the mini-TOSLINK connector was created to allow optical audio connections in the same form factor as a 3.5mm audio jack, and indeed to combine optical audio and analog audio into a single port. This by the way is perhaps the greatest proof that they keying in the standard TOSLINK connector was completely unnecessary unless they had future plans. The TOSLINK part of this is just an itty bit longer than a normal audio jack, just to make sure that when you plug in headphones or whatever you don’t poke the LED or photodiode. Fun fact! I didn’t know this was a thing until I was messing about with my Chromecast Audio, unplugged the audio cable from it, and the hole started glowing. I kid you not, I did not know Mini-TOSLINK was a thing, and I learned about it by accident. I don’t know exactly how common it is in the grand scheme of things, but it allowed portable devices like this MiniDisc Walkman to record from an optical source. Neat. Apparently it was found in some laptops and other random junk. I hope it wasn’t, like, super common and I’ve just missed this until 2016 or whatever. By the way. If you go to Amazon and search “toslink cable” you’ll find that some of the more popular options feature gold-plated connectors. [exasperated sigh] So far, optical audio connections have really withstood the test of time. It’s pretty impressive that a digital standard introduced in 1983 is still quite common in consumer audio visual equipment. Loads of new TVs feature an optical audio out, as do game consoles, Blu-Ray players, and even some streaming boxes. Recently, that’s started changing for reasons we’ll get into, but on the whole it’s still a pretty common sight in 2019. A large part of why it’s still so common is that in addition to uncompressed stereo PCM audio, TOSLINK also supported compressed 5.1 or 7.1 surround sound using Dolby Digital or DTS. Since loads of A/V receivers going back to the ‘90s will still be able to process at least some of the datastreams coming from a Blu-ray player or smart TV, it’s been remarkably future-proof. Also of note is that the physical specifications of TOSLINK were borrowed in the ADAT Lightpipe, or ADAT Optical Interface. This professional standard carries up to 8 channels of uncompressed PCM audio using the same hardware as garden variety TOSLINK connectors and cables, though this high-bandwidth signal is entirely incompatible with our old friend S/PDIF. So then, why is TOSLINK apparently on its way out? Well… because of the same thing I said was an advantage a few moments ago. It’s not been updated. Like, at all. One of the things Blu-ray brought us was uncompressed surround sound formats like Dolby TrueHD, and TOSLINK doesn’t have the bandwidth to support that. [angry yelling off-screen] YOU JUST SAID ADAT Lightpipe could carry 8 channels of PCM audio! You’re right, I did. But that’s not actually TOSLINK or S/PDIF. It just uses the same cable and connectors. [offscreen person mutters angrily] See, it would be relatively easy to just make the LED go blinky blinky a little faster and thus increase the bitrate of the data coming through the cable. But that means creating a new standard to be agreed upon by all the manufacturers out there. And, uh, that can be difficult! See, I can connect this brand new television to this A/V receiver from the ‘90s over TOSLINK precisely because the standard hasn’t really ever changed. If TOSLINK were updated, at the very least I’d need to tell the TV to downgrade its output to match this receiver’s expected input, and that can get messy fast. Remember, this is one-way communication. Easier to just never change it up, ya know? And then there’s this other thing called HDMI. Yeah, the Handy-Dandy Movie Input not only transmits digital video at a bitrate that will put your CD player to shame, but it also transmits digital audio at bitrates that will put your CD player to shame. Poor CD player. You’re doing alright. Since the very first HDMI version 1.0, debuting in December 2002, uncompressed 8 channel, 192 kilohertz, 24 bit PCM audio was supported. That’s like way more bits! With all that bandwidth, high-resolution sound is no problem at all. S/PDIF, and thus TOSLINK, sorta became obsolete once Blu-ray, and even HD-DVD, appeared on the scene offering lossless surround sound. HDMI could carry those signals no problem. Oh and HDMI 2.0 introduced 32 channel audio, so we're fine now. ALSO, in 2009 HDMI 1.4 introduced the audio-return channel, that’s why one of the HDMI inputs on your TV is labeled ARC. This sends audio back through the HDMI cable to enable your soundbar or home theater system to receive the audio that your TV itself is producing, such as when streaming video on a Smart TV or simply receiving over-the-air broadcast television. Yeah. HDMI has superseded TOSLINK on all fronts in the home theater space. As more sound bars and A/V receivers support the audio-return channel, TOSLINK increasingly finds itself in the legacy category. Which is still, just kinda weird! Fiber-optics are capable of some insane bandwidths, and while TOSLINK hails from the age of 10 megabyte hard drives, you’d think that we’d have seen more fiber optic standards in the home. In the next video, we’ll explore why fiber optics have remained little more than a novelty in the consumer space, and discuss whether any of our current everyday technologies could perhaps be better served with fiber optics. Thanks for watching. I hope you found this video to be as enlightening as it is digital. That is terrible. And yet. I still said it. Worse, I wrote it! I even wrote these words! How silly. But not as silly as selling TOSLINK cables with gold plated connectors and claiming that makes a superior connection! Anyway, I still think TOSLINK is pretty neat and even futuristic, even though it’s pushing 40 years old now. As always, thank you to everyone who supports this channel through Patreon, particularly the fine folks you see scrolling up your screen. Contributions from viewers like you make this channel sustainable and I owe you my thanks and appreciation. If you’d like to join these awesome people in supporting the channel with a pledge of your own, you can find a link to my Patreon page in the description. Thanks for your consideration, and I’ll see you next time! ♫ optically smooth jazz ♫ ...communication technology. On our increasingly connected planet, nearly everything we do from making a phone ca… I didn’t get very far! Since the only wat that, whoops? Uncompressed digital surround formats. That line is wrong!!! Oh no!!!!! That take might have been fine, but there were some weird bits. Also of note is that the physical specifications of TOS… Whe.. *clears throat* Pairs of copper wire that need to be made more precisely and with higher tolerances euch… AUGH! We are on the second line, and recording is… [unintelligible]

Channel: Technology Connections

Views: 1,486,767

Keywords: TOSLINK, toslink, toshiba-link, fiber optic, fiber optics, laser, LED, communications, S/PDIF, SPDIF, dolby digital, DTS, optical audio, optical, optical cable, technology connections

Id: ICcEOXVZ3F0

Length: 20min 46sec (1246 seconds)

Published: Fri Jul 19 2019

Reddit Comments

[u/TechConnectify]

Don't get me started on ground loops...

[u/YM_Industries]

I love Handy Dandy Movie Input.

[u/IsoOfYourLife]

I was always curious about the red light on the back of my equipment. I've only had to deal with fiber optic stuff once and it was because mice loved chewing the wires. they didn't touch the power or ethernet, just the expensive fiber.

also

ready to pump that pulsing light into another device.

that's what s/he said.

[u/rickane58]

I mentioned this in the comments on youtube, but TOSLINK also suffers fragility problems compared to copper. The bend radius of optical fiber is commonly 10-15x the diameter of the cable compared to merely 4x for copper. And frequently, copper cable can be unbent if overbent and will generally work well enough, while shattered optical fiber will leak light like a sieve since the total internal reflection that the fiber relies on is lost.

Definitely something I hope is discussed in the "Fiber for the home consumer" video that was touched on at the end of this one.

[u/mobyhead1]

I’ve actually used optical connections on home audio equipment, on occasion. A laserdisc or a DVD or a CD player, and I even had a Mac Mini plugged into my home theater receiver using a TOSLINK adapter shaped like a 3.5mm headphone plug.

Edit: watching the video...ah, yes. That was a Mini-TOSLINK adapter I used with my previous Mac Mini. Why? Because the Mac Mini would otherwise have output an analog stereo signal from that jack, and I wanted the audio it produced to remain in the digital domain (and possibly multi-channel) as it was sent to the receiver.

Nowadays, my Mac Mini connects to my home theater receiver via HDMI.

[u/whereami1928]

Yeah, I found the mini-TOSLINK stuff on my Macbook once a few years ago! I plugged in some headphones, and when I took them out, the port was glowing red. Thought I broke it, then I found out about optical out on it.

[u/kiwipie94]

Now I'm tempted to but a small Toslink DAC for my Chromecast audio, though I'm sure I wouldn't notice any improvement.

[u/razorbeamz]

I left a comment about this on the video but I feel like it's more likely you'll see it here. Here in Japan I have fiber optic internet running straight into my apartment and then into my modem through NTT FLET'S Hikari.

It might be interesting for you to look into the tech behind fiber optic internet, both private and for business.

[u/faraway_hotel]

Holy crap! Even if the system as a whole is on the way out, "gold-plated TOSLINK" will be hard to beat as a standard for Cable Dumb.