Spdif optical port: What Is S/PDIF? A Basic Definition

8 января, 2023

SPDIF vs. Optical – What Is SPDIF and What Is Optical?

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Let’s say you’ve ordered a Focusrite Saffire Pro 24 DSP or similar audio interface. You see “Optical In” and “SPDIF In” ports on the back of the device. Now this might trigger your curiosity. What’s the difference between an optical connector and an SPDIF connector exactly? Why are there separate interfaces for both on this device, like it’s a debate of spdif vs optical? According to Focusrite, the input for optical cables is used to add extra instrument inputs digitally. Meanwhile, is SPDIF capable of delivering full-quality output to your DAC?

The Sony/Philips Digital Interconnect Format—also known as S/PDIF or SPDIF—is a digital audio interconnect present in consumer audio equipment like the abovementioned Focusrite Saffire Pro 24 DSP. It’s responsible for outputting audio over short distances. Its signal is transmitted over fiber-optic cables with Toslink (or TOSLINK) connectors or coaxial cables with RCA connectors.

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What Is The Deal with SPDIF and Optical Cables?

SPDIF can be used with optical cables and coaxial cables, while the optical port can only be used with optical cables alone. If you have an optical cable, you can use the SPDIF or optical output. You can also use both. Optical and SPDIF outputs are both digital connections (the RCA connector found in coaxial cables used in SPDIF shouldn’t be confused with the analog RCA format). To wit:

  • What Is SPDIF? SPDIF stands for the Sony/Philips Digital Interconnect Format. It’s also known as the Sony Philips Digital Interface, using the same acronym. Obviously, Sony and Philips were the primary designers of this format that was standardized in IEC 60958 as IEC 60958 Type II. It can be sent over coaxial or optical cables. It works with either type of cable. This is because SPDIF is the encoding or data link protocol, not the wire or cable that runs it over.

SPDIF is a format that interconnects components in home entertainment systems or home theaters with high-fidelity digital systems for sound and music. It’s based on the AES3 interconnect standard and carries two channels of uncompressed PCM audio or compressed 5.1/7.1 surround sound, such as the DTS audio codec. It’s unable to support lossless surround formats that use up a bigger amount of bandwidth.

 

  • What Is Optical? Toslink or optical is a format that transmits signals through light and fiber optics. To be more specific, optical or fiber-optic cables transfer info through the beamed light via a plastic or glass fiber optic medium. The optical format itself usually refers to the ADAT protocol running over a fiber-optic cable since optical cables can be used in other formats, such as the SPDIF above.

With the optical format, the output signal that travels through the cable must be changed or converted from electrical to optical or light-based. After the signal reaches the optical receiver or input, it undergoes conversion from optical to electric. Optical was partly developed in order to combat Radio Frequency Interference (RFI) and Electromagnetic Interference (EMI) that coaxial cables are susceptible to. It also doesn’t lose signal over distances. It’s because light doesn’t suffer from attenuation or resistance found in copper cables.

 

  • The Main Differences of The Formats: Optical (the format, not the cable) and SPDIF are both digital connection protocols. The ADAT protocol for optical travels across Toslink or fiber optics while SPDIF is usually transmitted over a coaxial cable with an RCA jack but can also make use of Toslink as well. SPDIF, however, works with only 2 channels of audio or in stereo, while optical is capable of carrying 8 channels instead at 44.1 or 48 Kilohertz (kHz). In certain situations, it’s 4 channels at 88.2 or 96 kHz instead.

 

  • Why Not Use Both? It’s great to have both outputs present for sound systems like Focusrite Octopre, Audient ASP800, Behringer ADA8200, and so forth. Yes, in this instance, you can have your cake and eat it too. These multi-channel preamp boxes are capable of outputting 8 channels through the ADAT protocol. This is great for adding channels for full-band tracking, live recording, or drums and other instruments. Meanwhile, single or dual-channel preamps with a digital output will usually output the SPDIF signal over a coaxial or optical cable.

 

  • Why Even Bother with Using SPDIF? Some beginners attempting to hook up their sound system might feel like the presence of SPDIF is redundant and not needed since the “superior” Toslink or optical format with ADAT protocol uses more channels than the “inferior” stereo-channel digital audio interconnect. However, don’t be blinded by the specs and raw numbers. You don’t always need to use all 4-8 channels. Having SPDIF around also means you can use the external DAC or monitors with the digital output if you so choose.

 

  • SPDIF Makes Interfacing Multiple Units Very Easy: SPDIF is an important output option because you can use it with an external Digital Analog Converter (DAC) or digital-output monitors in order to make interfacing multiple units as effortless as possible. This is because digital connections like SPDIF carry the clock signal along with other signals (with HDMI, it is Red, Blue, Green, and Clock). This way, you won’t need to use a different USB DAC every time and try to make it work with your Focusrite Saffire audio interface and other units.

 

Which Should You Use?

 

Either is fine as long as you know what you’re in for with the SPDIF or optical format. Optical carries 8 channels at 44.1/48 kHz while SPDIF carries only 2 channels or is in stereo. It depends on the usage and the circumstance since SPDIF-enabled equipment will output SPDIF anyway if you don’t need those extra channels. SPDIF is essentially an alternative communication protocol to ADAT that uses coaxial and optical cables. What’s more, a coaxial has a more secure and stable RCA jack.

You can link up your optical and SPDIF ports on your preamp box with either two optical cables or one optical cable and one coaxial cable, respectively. Coaxial with SPDIF might also be the way to go since the more expensive optical cables can’t be bent or pinched tightly. Fiber optics tend to be more sensitive to damage versus copper wires, even though the latter is, in turn, susceptible to attenuation and interferences from RFI or EMI. With that said, at least with SPDIF you can switch from optical to coaxial cables when an optical cable is damaged. This isn’t the case with the standard optical format.

References:

  • https://en.wikipedia.org/wiki/S/PDIF
  • https://www.lifewire.com/coaxial-vs-optical-digital-cable-3134605
  • https://www.head-fi.org/threads/is-spdif-and-optical-the-same-thing.441404/

James Core — https://finddiffer.com/

Hey there, I’m James.
I created FindDiffer.com, a website that helps people with their tech and electronics questions. I love to help others, and I’m always happy to answer any questions people have about technology!
I finished Cornell University a few years ago, and now I live in the US. In my spare time, I like to work on new projects and play around with electronics. I also love spending time with my friends and family. Thanks for checking out my bio!

How to Use the Optical Out (S/PDIF) Port on Your PC

There are many ways to connect a PC to an audio system, but not all of them are equal. For the best results, you’ll have to use an optical audio cable. Read on to learn how to make use of the Optical Out (S/PDIF) port on your PC to set up such a connection, and enjoy the best your PC’s audio system and audio setup can offer.

Note: for this to work, both your PC and audio system must be equipped with optical ports.

How to Enable Optical (S/PDIF) Audio on PC

First of all, there’s the obvious matter of making sure that both your speakers and your PC have an optical (S/PDIF) port. With that off the list, simply plug your PC into your speakers using an optical cable.

Note: if you’re using a full-blown audio setup that includes an amplifier instead of a standalone speaker setup, double-check the optical connection you’re using. Your system might offer different ports for optical-IN and optical-OUT. You want to connect your PC’s output to your speaker’s input.

As with any cable format, companies will try to claim that their cable is better than others due to gold plating, “High Quality,” or other marketing jargon, but ignore all that. Buying a cheap optical cable should be absolutely fine unless you plan to tie it up in knots. Optical cables work in a similar way to HDMI in that they send digital signals that aren’t really subject to degradation. The main difference is that audio data uses less bandwidth than HDMI, so even if the quality of a cable isn’t great, you’re not likely to be affected.

Once the optical cable is plugged in, click the speaker icon at the bottom-right corner of your Windows taskbar, then click the speaker name above the volume slider to see if an “Optical” or “Digital” sound output has shown up. If it has, just click to enable it.

If the speaker doesn’t show up there, then right-click the speaker icon in the taskbar, click Sounds, and then the Playback tab.

Right-click anywhere in the Playback tab list, then click “Show Disabled Devices.”

At this point, a device called something like “digital output” or “optical output” should show up. Right-click it and click “Enable” to switch it on. Once you’ve done that, right-click it again and click “Set as default device.” You should now have optical audio enabled.

How to Enable Optical 5.1 Surround Sound on PC

Analog sound might still be okay for typical stereo setups. Still, when you enter 5.1 territory and modern sound formats like DTS, you just need a digital connection. If you don’t have one, audio decoding happens on your PC instead of your audio setup’s specialized hardware. The audio is then transferred there as lower-quality analog.

Getting the connection to work may not be the most straightforward affair. Still, you should prefer using a standalone optical connection for your audio instead of an HDMI port. HDMI audio might be somewhat easier to set up but comes with significant limitations.

HDMI has limited bandwidth and is used primarily for transferring video. Are you transferring high-rate video or playing games at ultra-high resolutions and over 60fps? Your HDMI might not have enough bandwidth to also transfer uncompressed 5.1 digital audio to your speakers.

By using two dedicated cables for video and audio, you’re offering each their own pathway to your audiovisual setup for the best possible results. However, there are some caveats.

First of all, is your motherboard capable of outputting 5.1 surround sound? Just because there’s an optical out port doesn’t guarantee that you’ll get surround sound across all your games, movies and so on. Your optical port on your motherboard should support 5.1 sound, though this will vary greatly depending on which Windows version you’re on, whether it registers as a Dolby-compatible output, and so on.

You can check to see if your setup supports one of the Dolby 5.1 formats by going to the Sound window -> Playback. Right-click your device, click Properties, then the Advanced tab. Simply click the drop-down menu, select “DTS Interactive” or whichever 5.1 surround setup you want to use, then click OK. (If your PC doesn’t detect Dolby Digital, then you may have some work to do, and we’ve offered links to some workarounds in the conclusion.)

You should also click the “Supported Formats” tab to make sure that the formats your receiver is capable of handling are ticked.

Check your App’s Settings

In some cases, you may find that although you’ve done everything correctly, you may not hear sound from some apps on your speakers. Some may do something that seems stranger, entirely ignore your multi-speaker setup, and only play audio from the front left and right speakers. When that happens, it’s time to look into your app’s settings.

Each piece of software on Windows can sidestep the default audio setting. Your media player of choice may have “locked” on your analog output and not caught on to the system-wide change you made to your new digital-out connection.

On a similar note, apps like Kodi offer options for managing your audio output. Through those, you can usually change the audio output device, encoding, number of channels, etc.

When some pieces of audio only play in stereo, you can find the solution on either your standalone speakers, your amplifier, or your PC’s audio software. By default, multi-speaker setups play stereo streams from only two speakers since that’s the way the audio “was meant to be.” It was recorded in stereo, so it plays in stereo, using only two speakers.

To have stereo two-channel audio play from all speakers, you should look for any options that look like “Stereo Expansion,” “Channel Redirection,” or into any “Surround Effects” available.

Conclusion

That should give you the basics of using an optical cable on Windows 10. The thing is, there is much nuance to it and many variables where things could go wrong. It’s not just your sound card and speakers that need to support it – it’s also the individual media you’re using, as well as the fact that recent Windows versions have made optical out support rather buggy. (You can no longer use the “Configure” button in the Sound window, for example, to enable 5.1 speakers.)

Odysseas Kourafalos

OK’s real life started at around 10, when he got his first computer — a Commodore 128. Since then, he’s been melting keycaps by typing 24/7, trying to spread The Word Of Tech to anyone interested enough to listen. Or, rather, read.

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DIY

Optical S/PDIF for PC / Habr

Digital interfaces have long been crowding out their analog ancestors. Mid-range audio systems use sound encoded in one of the many standards as a signal source. It can be the banal PCM for stereo sound or the Dolby family of standards for their multi-channel relatives. But today we will not talk about encoding methods, but about how exactly the signal is transmitted. There are only two options — optical and coaxial cable. The optics guarantee complete electrical isolation, the coaxial cable is easy to connect.

For ten years almost every motherboard has been equipped with an optical digital S/PDIF output (aka TOSLINK). But if you look at the back panel, you can not always find it. What’s the catch? The manufacturer is unwilling to install another connector on the rear panel and increase the cost of the board by installing an optical module or a coaxial cable jack. If you open the documentation for the motherboard, you can find a typical set of four pins similar to a speaker jack.

On the same page there is a branded bar with coaxial and optical outputs. Sometimes there are still optical inputs, but the author of the article only read about this on the net. Finding the original bar can turn into a non-trivial task — the price at foreign auctions is about $ 10, excluding shipping. A quick search of the Russian-speaking forums only finds requests to buy it and advice to buy a sound card with the appropriate slot instead.

So, we will make the bar ourselves. Despite the potential ease of manufacture, nothing similar was found for an optical connection on the network. There is more information on coaxial connection — but we want optics. So let’s start reading the documentation, for example here, S/PDIF Documentation.

According to the specification, the signal level on the motherboard is TTL, one can only guess about the load capacity of the SPDIFOUT output. The same documentation recommends loading it with an LED with a current-limiting resistor — this will be the cheapest connection. I did not dare to try this option first for two reasons — it was a pity for the board and the urgent need to stick a standard optical cable somewhere. Later, I nevertheless assembled an emitter follower on one transistor and connected an LED. The interface glowed cheerfully with a red LED, but the optical cable attached to it gave no sound. All the same documentation recommended picking up a super-bright LED with a wavelength of 660 nanometers. Perhaps none of the used LEDs fit.

The next step is to connect the recommended optical module TOTX173. The price and availability in online stores are again not encouraging — a little less than the same ten dollars and a long delivery. So it’s time to look for a donor. Having run through the home electronics dump, only one victim was identified, it turned out to be a Playstation 2, donated by employees for the last birthday. The hand on vandalism of the legendary prefix did not rise. At a regional online auction, a Samsung DVD Recorder was caught for the same sacred $10 without delivery. Photos will follow.

S/PDIF on the victim looked like this

Since the search for the code on the case (T2002H7) did not give anything, the device had to be turned on in the disassembled state in order to make sure that it was using five volts and a TTL signal level.

There are only three contacts, the common one is easily determined, the power is connected directly to the signed 5V plug, the information output remains connected through a 220 Ohm resistor. Here’s a close-up of our newfound module.

It remains to connect to the motherboard and assemble it all in the form of a bar. We connect the common output to the common one, power to power, and SPDIFOUT through a 220 Ohm resistor to data. We assemble a bar for a PC from a piece of a breadboard and a burnt out network card, I did it like this.

Installed in the housing.

More than two weeks have passed since the assembly — everything works fine. By ear, of course, the difference is within the limits of sensations given by psychology. But if there is acoustics that understands optics, why not use a do-it-yourself connection. In the comments, it would be interesting to hear an opinion about the possible difference in the sound of such an optical output and that obtained from a mid-range sound card.

After assembling, I got to the nearest home appliance repair shop. It was there that one should immediately look for a donor — they have a sufficient number of burnt DVD players, about a dollar for a fee. For those who want to repeat the design — it will be useful.

what is it, types, pros and cons of the connector. What is the difference between TOSLINK and S/PDIF?

Contents

  1. What is S/PDIF?
  2. History of S/PDIF
  3. How S/PDIF works and features
  4. Types of S/PDIF
  5. In what technique can you find S/PDIF output?
  6. Features of S/PDIF output on TV
  7. S/PDIF receiver: what is it and why is it needed
  8. How to choose the right S/PDIF cable, which is better coaxial or optical
  9. TOSLINK and S/PDIF: what is the difference
  10. Yes Is the future of S/PDIF output

What is S/PDIF?

S/PDIF is a connector for transferring digital audio between audio equipment. Various specifications apply here, relating to the hardware implementation as well as the low-level protocol. S/PDIF is often used to transmit CD (44.1 kHz) and DAT (48 kHz) signals.

History of S/PDIF

S/PDIF is the brainchild of Philips and Sony. The interface was created on the basis of the AES / EBU professional level standard, but gained a more simplified look. From the very beginning, it was planned that with the help of S / PDIF it would transmit sound only from CDs. It was also only about stereophony. But gradually the interface was refined, and the number of supported formats was constantly growing. As a result, the standard has learned to work with 7.1 and 5.1 sound. In this case, the stream is compressed and restored using a decoder.

The principle of operation and characteristics of S/PDIF

S/PDIF itself is implemented using a «tulip» (RCA) and electrical (coaxial) cable, where the impedance is 75 ohms. Such a cord will be ideal if the distance between devices is two meters or more. For the shortest possible distances, the usual RCA-RCA is also suitable. At the same time, the most progressive option for today is the option of connecting via a fiber optic cable using a laser beam (TOSLINK or OpticalOut).

As already noted, S/PDIF is designed to work with stereo sound, but now also supports compressed multi-channel sound. This was made possible by expanding the allowed speed from 150 kilobytes per second to 1.536 megabits per second. It uses pulse code modulation to transmit sound. Moreover, the information is split into separate packets (32 bits), and the free space in them can be filled with zeros. In addition to the sound itself, data is transmitted on the number of channels, as well as the track (track) number.

Types of S/PDIF

Today S/PDIF is implemented in several types:

  • Electric. In this case, a coaxial cable is used, the resistance of which at the input and output reaches 75 ohms. It connects with RCA connectors. At a distance of up to half a meter, you can use a standard audio cable «tulip». Its output voltage is 1 volt p-p, under load — 0.5 volts. If a long cable is used (more than 5 meters), there may be losses.
  • Optical. A fiber optic cable (TOSLINK) is involved. This option is distinguished by the work of the laser beam, which does not fade even at significant distances. Of particular popularity was the MiniTOSLINK connector, which is very common in various laptops. it combines headphone and S/PDIF outputs.

In what technique can you find the S/PDIF output?

This output was originally found in CD players and DVD players that accept discs.

However, over time, it began to be used in many audio devices. There is an output in TVs, players, sound cards for PCs, in car radios, home theaters.

Features of the S/PDIF output on the TV

The S/PDIF output on this device is required in order to output and transmit the audio signal in the desired format. When TV is broadcasting in high quality and 5.1 format is supported, then sound is output from the equipment in optical or digital format. Modern TV models are usually equipped with coaxial or Toslink connectors.

S/PDIF receiver: what it is and why you need it

If you need to connect a DVD player to a home theater receiver, then the S/PDIF interface will be a great option. This will allow the transmission of digital surround sound that is pre-compressed. At the same time, DTS and Dolby Digital formats must be supported.

How to choose the right S / PDIF cable, which is better coaxial or optical

When buying, pay attention to the length of the cable. Without the use of an appropriate signal amplifier, it should be no more than five meters. In addition, it is important to pay attention to which tape is supported by the selected cable. The optimal range is considered to be from 9MHz up to 11 MHz. The higher the numbers, the better the cable material. It is worth noting that borosilicate glass products are more valued. Plastic is considered the easier option.

For any type of connection, the transmission of information is the same. There is no big difference in transmitting optically or electrically. However, the latter option is more common and affordable. Fiber optics are a little harder to find, especially if you look in your inventory. But there are adherents of the theory that the optical connection suffers less from interference. Therefore, it is easier to use when a lot of other electronics are connected. Its disadvantages include fragility when laying. It is preferable to twist such a cable with a wide loop. If you put sharper angles with turns, then you should pay attention to the coaxial cable. In terms of range, both options are identical. They have a maximum transmission distance of 10 meters. The advantages of optics here include the fact that from 5 meters the laser beam will not fade, unlike an electrical signal.

This interface works with fiber optic TOSLINK connector or coaxial cable with RCA connectors. The actual signal for both options is the same. But TOSLINK on coaxial cable has a higher signal instability. Fiber is most often associated with S / PDIF, as it is more modern and in demand.

S/PDIF pros and cons

Pros:

  • Transmits compressed surround sound.
  • Lossless stereo transmission in PCM format.
  • Spdif is almost immune to external influences.
  • Relevant when connection of equipment with HDMI interfaces is not available.

Disadvantages:

  • Limited throughput.
  • Not capable of streaming DTS-HD Master Audio and Dolby TrueHD.

Is there a future for S/PDIF output

S/PDIF output is inferior to some modern audio transmission methods in terms of small audio transmission and data transmission distance. It can be used in individual cases when it is necessary or there are no other options.