What is optical audio?

The term might seem contradictory, much like the jazz waltz 'Ugly Beauty,' but there’s nothing dissonant about converting electrical signals into light waves for delivering rich, high-fidelity sound. It’s merely a step in the ongoing evolution of audio, as groundbreaking as Thelonious Monk's musical pieces. From mono to stereo to surround sound, or from analog to digital to high-definition, the progress continues.

Once upon a time, televisions and stereo systems were merely bulky wooden boxes. They were standalone units, with their connectivity limited to antenna ports and speaker terminals. Today, we find ourselves surrounded by an array of devices including tuners, amplifiers, game consoles, DVRs, VCRs, DVDs, Blu-rays, and outdated VHS players, not to mention the cassette player you keep relocating but likely haven’t even bothered to connect.

What are all those jacks for, anyway?

Just as you wouldn't use rusty old pipes to carry Pellegrino, there’s no sense in sending high-quality audio through outdated jacks, wires, and electronics. So, as companies work on improving audio and video standards along with storage media, they also innovate better ways to transmit sound and vision clearly from your device to your ear. This is why the back of our entertainment setups look like a 1960s Manhattan switchboard.

This is a fitting comparison, given that the first analog audio jack, the triple contact plug, or TRS connector, was adapted from the jacks used in telephone exchanges. The tip, ring, and sleeve design, in which three separate sections of the prong handled the left channel, right channel, and ground, respectively, was so effective that it remains in wide use today [sources: International Textbook Company; Modern Home Theater].

The Radio Corporation of America introduced its famous RCA jacks in the late 1940s, but the format didn’t gain widespread popularity until the early '70s. Much like the Supremes, these plugs come in groups of three – typically red, white, and yellow – with each consisting of a signal-carrying pin surrounded by a ground ring [source: Modern Home Theater]. Other variants of RCA jacks support composite and component video, as well as digital audio.

Component and composite cables carry video signals but lack audio. Composite cables, usually identified by a yellow RCA jack, consolidate all the video data into a single signal, while component cables break it down into three separate channels, each carried by a distinct plug [source: Maxim Integrated Products].

Both require a separate cable for audio transmission, bringing us back to RCA jacks and other copper-wire solutions – as well as an alternative: optical audio.

Copper-based wires face two challenges, which vary depending on their shielding and quality: interference from external electromagnetic noise and resistance in the wires that weakens the signal over distance.

Optical audio is unaffected by the first issue and can eliminate the second if the cable quality is sufficient, though it comes with its own set of challenges.

The Laser Light Show, or Tangled Up in Blu-ray

As anyone who has experienced a poor landline connection or a weak signal from a cable box can attest, signal degradation can be incredibly frustrating.

Copper, still the foundation of most wiring, can experience considerable signal degradation as the distance increases. Coaxial cable, which is used for transmitting television, telephone, and computer network signals, is equipped with shielding to prevent signal loss. However, losses caused by electrical resistance still diminish the signal over long distances. While shielded audio cables offer some protection against external interference, they still encounter the same resistance-related issues [source: National Instruments].

Fortunately, we have fiber optics.

Fiber-optic cables provide the low signal loss and high data rates that both telephone and Internet users require, transmitting information as light through thin strands of plastic or glass. These cables utilize total internal reflectance, ensuring that light bounces inside them without escaping. Glass fibers can carry these "lossless" signals over great distances without needing any signal amplification [sources: Encyclopaedia Britannica; Wood].

In the same way, optical audio surpasses older copper-wire connectors by converting electrical signals into light and transmitting them through optical fiber, resulting in superior sound quality.

The era of optical audio began in the 1980s when Toshiba introduced Toslink, the first optical audio cable. The Japanese electronics company, which had developed its own compact disc player, sought a way to output the enhanced digital audio quality to speakers and headphones. Naturally, Toshiba opted for an optical solution for CDs, an optical storage medium [sources: Modern Home Theater; Toshiba].

In an optical audio setup, the digital electrical signal from the source, like a DVD player, is converted into light by a device called a transmission module. In Toslink systems, this module typically consists of an LED (light-emitting diode) and a drive circuit, often transmitted through plastic fiber, whereas ST Fiber Optic uses glass fiber with a red laser at a 680-nanometer wavelength [sources: Modern Home Theater; Toshiba]. The signal then travels along the optical cable to the destination device, usually a television or audio receiver, where a light reception module transforms it back into a digital electrical signal. From there, it is sent to your speakers or headphones.

Since it only carries sound, an optical audio cable is generally paired with a video-only cable, such as DVI (Digital Visual Interface) or S-video.

So, what's the drawback? Optical cables can be somewhat fragile, and plastic versions aren't as 'lossless' as their glass counterparts. Additionally, the process of converting light back into an electrical signal can sometimes introduce errors. More critically, some argue that HDMI (see sidebar) has rendered optical audio outdated [source: Johnson].

Who is correct? As with many debates among audiophiles, the truth lies in the ear of the listener.