Optical

Overview

The term "Optical" is used in audio as an abbreviation to describe a form of digital audio interface that employs fiber optic connections. The format is typically S-PDIF of AES.

Basics

The most common type of optical digital audio interface is a form of S-PDIF which is identical to the coaxial electrical version except that the signal is in the form of an optical signal instead of an electronic signal.

The primary advantage of an optical interface is the complete lack of electrical connection, which eliminates many interface “noise” issues such as ground loops. This played a large role in the adoption of the optical format for consumer digital audio interconnection.

It is also possible to transmit other formats over optical connections, such as AES3, MADI, or ADAT. These formats are not compatible with each other, although it is possible that some devices may accept an AES3 stereo digital audio signal in place of the S-PDIF format because the audio portion of the two formats is identical.

There are also other forms of optical connectors use in digital audio, but they are more likely to be specific to a certain brand of equipment and are typically used for high data-rate applications such as multi-channel MADI or “Ethernet” based audio transmission.

Connections

Toslink

Toslink digital interconnects use a special form of connector developed originally by Toshiba Corporation. Shortly after its introduction by Toshiba it was adopted by Sony/Phillips for the consumer version of the professional AES digital audio format which they named “S-PDIF.”

Alesis Corporation adopted the Toslink style of connector for use in their proprietary ADAT optical format, which is a multi-channel format that is NOT compatible with S-PDIF. This can be a source of confusion as some digital audio interfaces have the option to select either the S-PDIF or ADAT format for their optical Input/output.

As digital video became a reality, multi-disc players became available that could also transmit Surround format audio signals or S-PDIF format from the same physical output.

3.5mm Mini

3.5mm Mini is used to refer to an optical connector that has the same general shape as a “mini headphone plug.” This allowed the same headphone jack to be used for either analog electrical connections for headphones or optical digital connections for connecting digital audio equipment.

One example of this is Apple® Corporation’ Macintosh® computers. Most Macintosh models have this type of connection available in the headphone output jack.