Optical cable for TV: device, features, audio connection through a home theater

The vast majority of cables for media centers, computers, and audio and video equipment use electrical signals to communicate components. In this case, both analog and digital streams are transferred from device to device in the form of current pulses along the conductors. The exception in the class of hardware connectors is an optical audio cable for TV.

History and essence of technology

Optical signal transmission was a science fiction topic only a few decades ago. The ability to use the incredible speed and data density that light is capable of has been a cherished goal for communications pioneers. Back in the 1840s, physicists Daniel Colladon and Jacques Babinet demonstrated the ability of light to be reflected in a stream of water, and in 1854. another physicist John Tyndall proved that the luminous flux can be bent together with the carrier using the example of water falling into a reservoir from an illuminated pipe.

In 1880, Alexander Bell patented the optical telephone system, calling it a photophone, but the telephone he had previously created turned out to be more practical. The persistence of the inventor and his inspiration to send signals through the air was not enough to popularize the device - the atmosphere did not let the light through as reliably as the wires - electricity.

In the following decades, optical signals were used in some special cases of communication, for example, in the transmission of messages between ships. The photophone itself turned out to be an unclaimed invention before the discoveries of lasers and the breakthrough in fiber-optic technology. The experimental model was donated by Bell to the Smithsonian Institution and has remained on the shelf there to this day.

The rapid development of fiber-optic technologies took place in the second half of the 20th century. In the first communication systems, a laser was used as a source. But already in the 1980s, researchers developed a fiberglass-based fiber optic cable capable of transmitting a conventional light signal over long distances. Since that time, the technology has found practical application in telecommunication systems. Most modern standards for light transmission over fiber assume the following main stages of information transportation:

• creating an optical signal from an electrical one;
• retransmission of the signal through the fiber with the preservation of its strength and without distortion;
• reception of an optical signal;
• converting it to electrical.

The most commonly used transmitters are semiconductor devices (LEDs) that work optimally in the required modulation frequency range. The receiver is a photodetector in combination with an amplifier to recover a weakened or distorted signal. Fiber optic wire itself consists of the following components:

• Core. Made from extremely low refractive index material.
• Shell. Mirror coating for total internal reflection.

One of the peculiarities of light wires is the complexity of the connection at the cut. Such procedures require special equipment and micron precision. Therefore, for domestic use, only ready-made cables of multiple lengths are used.

TOSHIBA standard

The Toshiba-link interface standard, or TOSLINK, was introduced in 1983 by a well-known Japanese concern and was originally intended for use with branded turntables CDs. The optical signals transmitted through this port were of the same shape as the electrical ones, with the only difference that TOSLINK used pulses of red light to transmit. The laser was not used as a source; instead, a simple and inexpensive LED worked. The declared reliable transmission distance was limited to ten meters, but in practice it did not exceed five.

The moment Toshiba-link was born coincided with the beginning of the era of home theaters, which led to its presence. on audio and video components of household systems as an interface for transmitting digital data using Sveta. Since in TOSLINK only fiber-optic cable was used to transport the information flow, such switching in comparison with electrical had some undoubted advantages:

• insensitivity to electromagnetic interference;
• lack of its own electromagnetic radiation;
• the ability to provide complete galvanic isolation between equipment.

All these qualities are of great importance for sound-reproducing equipment, the designers of which spend a lot of effort on the fight against interference and pickup when switching units among themselves. For many music lovers, the appearance of such an interface has opened up new opportunities in building their own systems.

Over time, the presence of this type of optical connection has become almost the standard for televisions, receivers, DVD players, amplifiers, computer sound cards, and even game consoles. The main purpose of TOSLINK in consumer equipment is to provide the ability to losslessly process stereo and multichannel surround sound in formats such as DTS or Dolby Digital.

Comparison with HDMI

There are many ways to connect the sound of your TV through your home theater system to get the best results. The most popular method is HDMI connection. In this way, both audio and video signals can be transmitted. This interface has supplanted fiber optics to a secondary role, primarily because TOSLINK is able to carry only audio data and requires separate connection using component or composite cables for transmission video signal. This is not the only downside to optical connectivity.

In addition to its versatility benefits, HDMI offers comparatively higher bandwidth. For TOSLINK, new forms of surround sound such as Dolby Thrue HD and DTS-HD are beyond distortion-free transmission.

Despite the fact that the standard is more than thirty years old, it is still an actual interface. Optical cable is still attractive for up to 7.1 channels of high-definition audio. For most consumer installations, the difference will not be noticeable when using HDMI or TOSLINK.

One of the most common reasons for using a light connection is the presence of a large fleet of old high quality receivers with an optical input on board. For lovers of good sound, replacing them with new ones does not make sense. In addition, the vast majority of HDTV sets, Blu-ray players and game consoles still come with an optical port.

One of the reasons for interference in television and radio equipment is poor-quality grounding or its absence. This can cause hum in the speakers or even damage the equipment. In such cases, annoying distortion can be completely eliminated by isolating the devices from each other using an optical cable instead of the usual HDMI.

State-of-the-art technology has allowed TOSLINK to reach its ultimate performance. It has evolved with the purity of the optical conductor, the clarity of the lenses, and the flexibility without signal loss.

Optimization of these three parameters resulted in no audible difference compared to coaxial connection, therefore, Despite the versatility of HDMI, the humble optical cable for TV and home theater has not lost its values.

Purchase selection criteria

First of all, you need to make sure that the devices planned for connection are equipped with connectors designed for transmitting optical signals. This is an easily recognizable trapezoidal port with a plug and is usually marked with OPTICAL AUDIO, TOSLINK, or Digital Audio Out (Optical). When the device is turned on, it immediately draws attention to itself with a faint red glow around the port plug.

For fiber, there is no such noticeable difference in performance across brands or designs as there is for analog patch cables. In this sense, they are similar to other digital interfaces. In any case, when choosing an optical cable, you need to pay attention to the following:

• Length. It is very important that the required cable length does not exceed 5-10 meters. There are manufacturers who insist on the ability of their products to transmit a signal up to 30 meters without loss. But in this case, it is important to understand that the performance of such connectors will entirely depend on the class of transmitting and receiving devices.
• Materials (edit). Manufacturers usually do not publish manufacturing parameters in their specifications regarding the ideal cross-section. core or its deviations to ellipticity, which is the most significant quality characteristic manufacturing. But the material from which the fiber is made is usually indicated. Glass and silica cores are significantly higher in quality than plastic ones. In addition, thicker cables are more durable, and better ones come with a protective nylon fabric sheath.
• Bandwidth. The higher it is, the better. A good cable should have a bandwidth between 9 and 11 MHz. This metric is especially important for high sample rate multichannel audio.

In addition, a quality cable must be made from a variety of small diameter fibers. Monofilament products with a thickness of more than 200 microns are more susceptible to reflected signal attenuation than multifilament assemblies.

It is very important to pay attention to the condition of the cable and any indications that it has been bent or excessively twisted during storage or transportation. Such damage unambiguously leads to distortion of the transmitted signal or complete loss of performance.

Cinema connection

First of all, you need to remember that optical audio cables are not ordinary metal conductors that forgive indelicate handling. Fiber optic connectors should never be bent forcibly, and shock sensitivity should always be borne in mind. The very connection of TOSLINK to the TV is a simple procedure that does not require any tools or technical knowledge. Recommended sequence of actions:

1. Turn off the TV and the paired device.
2. Provide access to the interfaces of the switched equipment.
3. Remove the protective cap from one end of the cable and locate the TV's optical output socket. Insert the bare end of the cable into the socket.
4. Remove the protective cap from the other end of the cable and insert the bare end into the optical input connector.
5. Switch on the TV and the connected device. Select SPDIF OUT / TOSLINK in the audio output options menu and save the settings.
6. Adjust sound parameters if necessary.

It should be borne in mind that if the speakers or amplifiers used in the theater are not of high quality, even the most expensive optical cable will not be able to improve the sound. In such cases, you should not spend money on a fiber-optic connection, but rather experiment with other methods of switching.

Good cables can only prove themselves in a set with equipment of the appropriate class. The modern TOSLINK is capable of handling very complex tasks. Manufacturing processes and material handling capabilities in the 21st century have reached a level unattainable for of the time when the ability to transmit audio data with a luminous flux in household appliances caused Delight. High quality quartz, multi-fiber conductors, low core geometry aperture, great flexibility combined with low loss - these advances allow you to ensure flawless transmission of even the most complex multichannel audio tracks.