What is Digital Television?

Posted By BrokenClaw on March 5, 2008

The difference between an analog broadcast and a digital broadcast is difficult to explain without some prior knowledge of how radio and television signals get from the tower to your home in the first place. Suffice it to say that broadcast signals are a type of electromagnetic wave that carries data through space. How far those signals move through space is a function of the wavelength, frequency, and atmospheric and topographical conditions.

The science of an analog broadcast uses the same basic principles as the children’s toy of talking through two cans on the ends of a string. Instead of string, broadcasts use electromagnetic waves, but they propagate the data in the same way.

Until recently, all broadcasts were analog in nature. The data was essentially sent as a sound or a picture that could be reproduced and amplified by your receiver, either radio or television. Your receiver knew nothing about what was being played. The disadvantage of that system is that the broadcast has to overcome all sorts of interference which can distort the sound or picture.

A digital broadcast overcomes those obstacles by sending, not the sound or picture, but a digital description of the sound or picture, so your receiver can recreate them in their original form.

Imagine a professor giving a lecture on the sonnets of Elizabeth Barrett Browning. She projects a slide of Sonnet no. 43 onto a screen at the front of the lecture hall. That is an analog broadcast of the sonnet. A student’s ability to follow along is dependent on the brightness of the projector bulb, the focus of the slide, the location of their seat, the acuity of their eyesight, and the lighting in the room.

Now imagine that each student has the textbook with all the sonnets. This time, instead of projecting a slide, the professor simply announces the sonnet number to the class. The students open their book and find the correct sonnet. That was a digital broadcast. Instead of showing the poem to the class, the professor gave a digital description, the sonnet number, and the students are able to reproduce it perfectly themselves. None of those analog factors mattered. They only have to hear, or receive, the number 43.

The same principle applies to digital television. Instead of transmitting a whole picture, the digital signal describes every single dot on the television screen. The television itself already knows how to change the color of the dots. That is not to say that every digital television picture will look exactly the same, because it is still up the quality of the television to interpret the data and produce the picture. But every television will receive the same digital description.

All high-def TVs are digital, but not all digital TVs are high-def. Read about the Digital Television Transition.

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