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