Why are digital signals replacing analog signals?

Digital signals have replaced analog signals because they are easier to preserve, transmit, and copy. In the information age, digitization is an essential technology.

 

On December 31, 2012, all terrestrial stations in South Korea will stop broadcasting analog signals. Digital broadcasting, which has been piloted since 2000, will finally completely replace analog broadcasting. But what is digital broadcasting, or digital signal, and why is it replacing the old analog signal? Let’s briefly explain what digital is and its advantages and disadvantages.
The word “digital” is actually a very familiar word. For the past 20 years, it’s been used in electronics advertisements and in the news as a symbol of a new era. However, because it’s used in a symbolic sense, we often don’t know what it actually means. That’s why we need to understand what digital is.
To easily understand what digital means, we first need to understand “analog.” “Analog” means a quantity that changes in a “continuous” manner. In this context, “continuous” means that the magnitude of a value changes gradually over an intermediate process. For example, your height didn’t grow overnight, but rather gradually over the course of your school years, like 160 centimeters, 165 centimeters, 170 centimeters, and so on.
“Digital,” on the other hand, refers to a quantity that changes in “discrete” increments, which means that when something changes in magnitude, it does so abruptly, without any intermediate steps. Because a digital signal can only be integer multiples of a minimum value, there can be no non-integer values. If a person’s height is a digital value with a minimum value of 20 cm, then there are only two people who are 160 cm tall and one who is 180 cm tall, and no one in between.
Given the meaning of “digital” described above, you might ask, “Does digital exist in nature? The truth is, digital signals don’t exist in nature – the light, sound, and smells we experience are all analog signals. Digital signals are the processing of analog signals into digital signals by humans for human needs. It’s like when you’re graded on your 100-meter time in gym class and you get an A for under 15 seconds, a B for over 15 seconds and 17 seconds, and a C for everything else. An individual’s 100-meter time is “continuous,” but we’re processing it into a “discrete” value to score it as a grade. This is called “digitization.
So why do we need digital signals in the information age? To find out, we need to understand how the ‘digitization’ of an ‘analog’ signal actually works, despite the fact that analog signals are closer to nature’s signals.
In computers, ‘digital’ signals are represented by 0s and 1s. A computer interpreting a digital signal interprets an electrical signal as a 0 when no current is flowing and a 1 when current is flowing. These signals are sent in sequence according to a unit time (clock), such as ‘01010010….’. If the unit time is 0.1 seconds, then the computer will check every 0.1 seconds for the presence or absence of an electrical signal and read a digital signal like ‘01010010….’. So, when it comes to transmitting a ‘digital’ signal, all that matters is whether current is flowing or not.
Let’s go back to our gym class example. Let’s say you’ve divided the grades into A, B, C, and D based on the students’ records and defined A as ’00’, B as ’01’, C as ’10’, and D as ’11’. When you send the grade information to the computer, the computer will recognize the grade as A if the electrical signal over a unit of time is ’00’, B if it’s ’01’, C if it’s ’10’, and D if it’s ’11’, based on the above rules. Similarly, other analog signals are converted into ‘discrete’ digital signals, where each digit is defined as a 0 and a 1, which is then recognized by the computer.
Understanding this ‘digitization’ gives us three advantages in processing digital signals over analog signals.
First, signals that have been ‘digitized’ can be preserved permanently. Data stored as analog signals is continuous and can be altered over time by external influences such as moisture, temperature differences, and magnets. This is evidenced by the poor sound quality of poorly stored vinyl records. However, digital signals are only represented by 0s and 1s, so small external influences do not easily change the signal. For example, suppose your computer recognizes all values above 0.5 as 1. If a signal with a value of 1 is modulated by an external influence by ±0.1 to 0.2, the modulated value will eventually have a value within 0.8 to 1.2. However, since 0.8 to 1.2 are all values greater than 0.5, the computer will still recognize the modulated signal as a 1. This fact makes it easy to understand why data stored as digital signals is robust: in the absence of any external shock, digital data is preserved forever.
Second, ‘digitized’ signals can be transmitted and stored in the same way on a computer. As we saw earlier, light and sound signals can also be recorded as 0s and 1s through digitization, so computers store pictures, sounds, text, etc. as ‘digitized’ data, which are all 0s and 1s. Similarly, when a picture file is transferred to another computer, it is also transferred as ‘digitized’ data consisting of 0s and 1s. In other words, since computers recognize ‘digitized’ pictures, sounds, and characters as 0s and 1s, even different kinds of data can be transferred and stored in one way (a combination of 0s and 1s), which is the strength of computers’ universality.
Third, “digitized” signals can be easily manipulated by computer programs. Manipulating analog signals requires external influences, which makes it difficult to manipulate only the parts you want, whereas digital signals are very easy to manipulate by simply changing the order of the zeros and ones through a computer program. For example, if you have a wrinkle on your face in a photographic print, it is difficult to erase the wrinkle without erasing the area around it with acetone, but if it is digitized and stored in a computer, you can easily remove the wrinkle by modifying the data with Photoshop.
In conclusion, digital signals have advantages over analog signals in preservation, storage, transmission, and copying. Therefore, the conversion of analog to digital signals has always been an important research topic in electronics, and it has become an essential technology in the information age.