S pdif optical out: What Is S/PDIF? A Basic Definition

SPDIF vs Optical (Differences & Reasons To Use Each)

Disclosure: We may receive commissions when you click our links and make purchases. Read our full affiliate disclosure here.

  • Confused about the differences between SPDIF and optical?
  • Wondering about the different use cases for each, and when to use one over the other?
  • We address all your commonly asked questions in this complete guide
  • Also, check out our guide to the differences between SPDIF and ADAT

Considering that SPDIF and optical are digital connections, some people might think they’re interchangeable or that SPDIF is a type of optical connection.

The truth is that SPDIF is a connection protocol that can sometimes use optical connections.

The first optical connection format, Toslink optical, was developed before SPDIF. As the audio industry has evolved, the use cases for each connection type have changed a bit, and depending on your workflow, you might find that one works better for you than the other.

SPDIF vs. Optical: A Quick History

SPDIF stands for Sony/Philips Digital Interconnect Format and was developed in 1980 by Sony and Philips for home theatre.

Optical, or TosLink optical, was manufactured by Toshiba in 1983 to connect CD players to receivers.

SPDIF vs Optical: The Differences

It’s important to note that SPDIF is simply the connection protocol rather than the cable or physical connection itself, whereas optical also refers to the cable or physical connection type.

  1. SPDIF uses electricity to transfer two digital high-fidelity uncompressed PCM audio channels or compressed 5.1 surround sound.
  2. Optical/TosLink utilizes fiber optic connections to transfer up to 8 channels of audio and is the standard protocol for ADAT audio transfers.
  SPDIF Optical
Signal quality Relatively noise-free but still susceptible to noise Clear, consistent signal
Interference Due to the physical properties of electromagnetic current, some interference is possible Free from interference due to the physical properties of light pulse technology
Use Cases Stereo audio in/out for DVD players, TVs, speakers and some pro audio Often used for transmitting Dolby decoders to sound equipment, consoles, and AV receivers
Limitations Only handles digital signals, and cannot support lossless surround formats Limited to 5. 1 and stereo channels, cannot support lossless surround formats like DTS-HD or Dolby TrueHD
Overview Useful for musicians working with digital signals prioritizing low-latency audio A great solution for general home theater and hi-fi usage, and those who will benefit from wide-range compatibility and better energy consumption

SPDIF vs Optical: When To Use Each

There are various reasons that you’ll want to use SPDIF rather than optical, and vice versa. Depending on your needs, one connection type might be better.

For music producers — it’s worth noting that your pro audio interface might offer you both connections. Some outboard preamps allow you to use the digital SPDIF out with an optical cable, while you can still get extra inputs via SPDIF in.

The main advantage of transferring audio via SPDIF is not just the capability for extra channels but also that you won’t need to convert your digital audio to an analog signal before transferring it to another device. Therefore, you’re less likely to lose quality in your audio signal. This makes them very attractive for pro audio use, and why you’ll see them in audio interfaces.

Optical is found commonly in home theater setups for their wide-range compatibility and better energy consumption. Nearly all audio devices and components will offer you optical connectivity.

Data Transfer Method and Connecting Multiple Audio Interfaces

SPDIF is generally better suited for connecting multiple audio interfaces because SPDIF will carry the clock source with the audio signal, meaning you won’t need multiple instances of DACs (Digital Analog Converters) to keep everything in sync.

This is called “digital clocking.” When you transfer digital audio from one device to another, it’s transmitted in a series of samples.

The more samples per second, the higher quality of the audio. To ensure the samples are being transmitted accurately, the device receiving the audio needs to know when each new sample will be played.

This is done using a “word clock,” a clock signal embedded in the SPDIF protocol.

It’s essential to use quality cables when you connect two devices via SPDIF. A subpar cable or shaky connection could result in a phenomenon known as “interface jitter” which can be heard as clicks and pops in the audio recording.

Cable Type

Depending on whether you’re using a SPDIF or optical connection in a recording studio versus a live setting, the cable type might be more important to you.

If you’re in a live setting, you’ll want a more durable cable that’s less expensive to replace if something happens during the show. In this case, there are a few things to keep in mind.

Even though copper wire is more vulnerable to interference, fiber-optic cables are more sensitive to physical damage.

Depending on the length of cable you need, it’s worth considering one over the other. If it’s a short run, you won’t have to weigh one risk factor against the other. If you need a longer cable length, you’ll need to be careful where you run it, especially in a live setting.

Number Of Audio Channels Transferred

If you need more than two channels of audio, SPDIF is your best bet, as it will give you up to 8 channels of audio. However, if you’re in a live setting, an optical cable might do the job instead since you’ll only need two tracks (which together make a left and right stereo mix).

One of the most versatile use cases for SPDIF is if you upgrade your audio interface and still want to use the old one for additional inputs and outputs. In this case, connecting the two via SPDIF would give you those eight extra audio channels.

SPDIF Connections Explained

TECH TIPS — SPDIF CONNECTIONS EXPLAINED

S/PDIF (Sony/Phillips Digital Interface) is a consumer audio connection standard for transmitting high-quality digital audio. It is primarily used for connecting home cinema (home theatre) systems, Hi-Fi, games consoles, set top boxes, computers, and other consumer entertainment devices. S/PDIF can carry two channels of uncompressed PCM audio or compressed 5. 1/7.1 surround sound such as Dolby Digital or DTS audio. The S/PDIF interface and the associated connectors can be implemented in two different ways “optical and coaxial”

OPTICAL 

 This implementation uses fibre optic cables that can be equipped with two different types of connectors — TOSLINK  and Mini Optical. Advantages of fibre optic as a transmission medium are immunity to electrical RF interference and ground loops, and, when using quality cable construction and materials, low signal attenuation meaning distances of up to 50m are supported (for example with Lindy Gold TOSLINK S/PDIF cable).

TOSLINK (abbreviated from Toshiba Link) is the most common connector type. You will typically find it on many larger consumer AV and Hi-Fi products such as amplifiers and set top boxes.

Mini-TOSLINK connectors are sometimes called MiniPlug or Mini Optical but they all refer to the same connector.

To browse the range of Lindy S/PDIF optical cables, click here.

Adapters can be used to convert a TOSLINK connector to Mini-TOSLINK. The mini-optical connector is typically used on audio devices, such as the Google Chromecast Audio, and laptops. Some laptops feature a combined Mini TOSLINK / 3.5mm audio socket as these connectors are physically very similar in size. Lindy Optical Audio (S/PDIF) cables are ideal for home cinema and audio devices in professional installations. 

COAXIAL

This version of the S/PDIF interface requires the use of RCA phono connectors and 75 Ohm coaxial cable. To comply with the specifications and operating standards of S/PDIF It is important that 75 Ohm cable is used rather than ‘standard’ phono cables which look physically the same. Without getting too technical, this is because it is important that the two devices connected by the cable must have matching impedances otherwise the interface may not function correctly and you may experience drop outs, audio jitter or no sound at all. 75 Ohm S/PDIF Coax cable can usually be distinguished from other ‘analogue’ phono / RCA cables by orange colour coding on the outside and / or inner connector housing.

OPTICAL VS COAXIAL – WHICH IS BEST?

The short answer is neither is better than the other. It depends on your application. It is important to understand that SPDIF refers to the interface, not the actual cable connection. For example, the RCA / Phono Coaxial cable can also be used for analogue audio and composite video connections. Similarly, optical as a connection medium can be used for purposes other than SPDIF. For example, optical cables support the ADAT Lightpipe optical interface which can carry 8 channels of digital audio at 24 bit resolution at 48kHz or 4 channels at 98kHz, whereas SPDIF is limited to two channels of audio. 

In terms of construction, optical cables are usually thinner and are likely to have a slightly more fragile construction than coaxial cables so if you need a portable connection or use equipment in a harsh environment such as on stage, coax might be the way to go. Conversely, in an environment where there is likely to be a source of EMI interference or longer cables runs are required, optical cables may be the preferred choice.

DIGITAL TO ANALOGUE CONVERSION

Many modern TVs are equipped with an optical port, this allows users to break out the audio to a dedicated sound system such a sound bar or surround sound amplifier. Optical, because it uses light to send the signal, will introduce very little delay in the audio meaning it does not affect the viewing and listening experience.

The latest TVs, due to their slim design, will often omit analogue audio outputs whilst still retaining the digital coaxial or optical (S/PDIF) outputs. A question we are often asked is how to use existing audio equipment, such as an older analogue amplifier and speaker set, to devices with newer digital connections. In this case users can use a Digital to Analogue Converter, commonly known as a DAC. 

Simply connect an optical cable from the digital audio, source such as a TV, and then connect that to the DAC which will then convert the digital signal to analogue, allowing the connection of your legacy equipment.  

For example, the Lindy DAC Pro

ANALOGUE TO DIGITAL CONVERSION

You may also find that you have an audio source that only has an analogue output such as a turntable, or media player. If you have a more modern amplifier or a sound bar that uses optical then you can still use these devices together by converting the older analogue signal to the newer digital optical or coaxial. 

For example the Lindy Stereo to S/PDIF Analogue to Digital Converter accepts a Left and Right Phono input, and converts the audio signal to either Coaxial or Optical S/PDIF digital signals. 

OPTICAL SWITCH

Should you have more than one optical signal you wish to send to your amplifier or speaker system, but do not want to have to unplug and re-connect cables each time you change device, then you can use a switch. Various types of Lindy optical switches are available. These allow users to connect one or more input device such as an Xbox, TV or computer, and then select which device (input) you wish to use. This is sent to the output for your amplifier, speaker etc.

See the Lindy range of S/PDIF switches here

OPTICAL SPLITTER

The opposite of a switch is a splitter. This allows users to connect a single audio source and send that audio to multiple sound systems at the same time. For example, you may have a media player, and wish to send the audio to speaker systems in multiple rooms, in this case you could use an optical splitter.

See the Lindy range of S/PDIF splitters here

S/PDIF digital interface and how it works

  • Main page
  • Stereo system
  • S/PDIF digital interface and how it works

Digital audio sources

  • CD player
  • SACD player
  • CD transport
  • Processors (DAC-DAC)
  • How do I select a digital source?
  • What to pay attention to when listening?
  • S/PDIF digital interface and how it works

Turntables

  • Drives
  • Tonearms
  • Cartridges
  • How to choose an LP player?
  • What to look for when listening?
  • Player setup

Everything about vinyl

Digital audio sources

S/PDIF digital interface and how it works

Digital output.

Socket on all CD transports and on some CD players that provides access to the digital data stream. With the digital output, the CD transport can feed information to a separate digital processor via the S/PDIF (Sony/Philips Digital Interface Format) interface. It is named after the two companies that invented the compact disc.

S/PDIF digital interface is a standard digital audio transmission format primarily between CD transport and digital processor. The S/PDIF signal can be transmitted through various types of connectors and cables, such as optical ST or coaxial (discussed later in this chapter). All consumer digital audio equipment—transports, digital processors, and digital recorders—uses the S/PDIF interface. The professional version of S/PDIF is called the AES/EBU interface (Audio Engineering Society/European Broadcast Union, or Society of Audio Engineers/European Broadcasting Union — the organizations that standardized this interface). Sometimes it is also used in consumer digital audio equipment.

Jitter are timing errors in the clock generator that sets the timing for converting CD digital samples into music. Jitter also degrades the sense of space by reducing soundstage depth and blurring musical imagery. The feeling of transparency of the air between you and the performer disappears, the space seems to be covered with a haze.

The main source of jitter in digital audio reproduction is the interface connecting the CD transport to the digital processor. Get rid of the digital interface, which is inherently lacking in a CD player, and you will destroy the main «pathogen» of jitter. For this reason, single-case CD players, other things being equal, have a significant superiority in sound quality over component equipment.

The S/PDIF signal contains the audio data of both audio channels, as well as a clock signal, also called a clock. These clock pulses are restored by the digital processor, so that the transport and the processor operate on the same time basis. An indicator labeled «Lock» or a sample rate indicator on the front panel of many digital processors indicates that the clock has recovered and the two components are in sync, ie. their clock rates are the same.

The data stream of the S/PDIF interface carries not only sound information, but also service information, including a number of CD subcodes. They contain information about the sampling rate, the use of pre-distortions, as well as information about whether the signal belongs to the professional AES / EBU interface or the interface for consumer equipment S / PDIF. The subcode data also includes all track numbers and time information displayed by the CD player or transport indicator. Audio data and subcode information are combined into 32-bit sounders. Each subframe starts with a preamble, a four-bit sync pattern that violates the biphasic coding rules. The preamble acts as a synchronization signal indicating the start of a new subframe. The preamble is followed by four bits of auxiliary information, 20 bits of audio information. If sixteen-bit audio information is transmitted, then the additional four bits are not used (replaced with zeros when encoding). The four-bit side data area can be used to accommodate audio data, increasing the total audio data word length to 24 bits.

An additional four bits (audio sample correctness, user data bit, audio channel status, and subframe parity) terminate the subframe.

Left and right audio channel subframes are identified by slightly different preambles. In a single bit stream, they are transmitted in turn. Blocks of 192 bits are formed from subframes. At a sampling rate of 44.1 kHz, the total bit rate is 2.8224 Mbps.

How to use the optical port (S/PDIF) in Windows 10

Windows

The optical output port on a PC remains a mystery to many people. Where it was placed in the back of your computer, it emits a constant red laser glow, whether or not anything is attached to it. It looks like you want to connect something to it, but what? The answer is logical: an optical audio cable, and here we will show you how to make it work, with the caveat that it becomes very difficult to use. Windows 10 operating system is correct in recent years.

How to enable optical (S/PDIF) sound on PC

First of all, there is an obvious problem — make sure that both your speakers and your computer have an optical (S/PDIF) port. If it’s not listed, just connect your computer to the speakers with an optical cable.

As with any other 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 it all. Buying a cheap optical cable should be ideal, unless you plan to tie it in knots. Optical cables work similarly to HDMI in transmitting digital signals with virtually no degradation in quality. The main difference is that audio data uses less bandwidth than HDMI, so even if the cable quality isn’t great, it’s unlikely to be affected.

After connecting the optical cable, click the speaker icon in the lower right corner of the Windows taskbar, then click the speaker name above the audio slider to see if «optical» or «digital» audio output is displayed. If it is present, just click to enable it.

If the speaker does not appear there, right-click the speaker icon on the taskbar, select Sounds and then the Playback tab.

Right-click anywhere on the Run tab and select Show Disabled Devices.

At this point, a device called something like «digital output» or «optical output» should appear. Right-click it and click «Enable» to enable it. After that, right-click it again and select «Set as default device». You should now have visual audio enabled.

How to Enable Optical 5.1 Surround Sound on a PC

The real benefits of an optical cable become apparent when you plan to use surround sound, but there are quite a few criteria your computer must meet. Also, as a general rule, if your receiver/speaker has an HDMI port, you should use that instead as it provides better 5.1 compatibility with Windows 10 drivers.0013

First of all, is the motherboard capable of outputting 5.1 surround sound? Having an optical output port does not guarantee that you will get surround sound in all games, movies, etc. The optical port on your motherboard should support 5.1 audio, although this will vary widely depending on which version of Windows you are using, whether it is recording it’s like a Dolby-compatible output, etc.

You can check if your installation supports Dolby 5.1 by going to the Sound -> Playback window. Right-click the device, select Properties, then the Advanced tab. Just click the drop down menu, select «DTS Interactive» or whatever 5.1 surround sound setting you want to use, then click OK. (If your computer does not detect Dolby Digital, you may need to work and we have provided links to some solutions in the feed.)

You must also click the Supported Formats tab to ensure that you select a format that the recipient can handle.

Conclusion

This should give you the basics of using an optical cable on the Windows 10 operating system. It is important to know that there are many nuances to this and many variables where things can go wrong.