In this blog post, we’ll compare the process of human speech and listening with the transmission and reception process of a radio to explore the principle by which a radio carries music signals on high-frequency radio waves and converts them back into sound that humans can hear.
SBS Power FM at 107.7 MHz, MBC FM4U at 91.9 MHz, KBS Classic FM at 93.1 MHz… These are the frequencies we commonly mention when referring to radio stations. But how can a radio receive radio waves with such high frequencies—measured in MHz—and produce sound? You might be wondering this. As of 2026, this type of FM broadcasting is still in use; for example, SBS Power FM broadcasts at 107.7 MHz, and MBC FM4U uses 91.9 MHz in the Seoul metropolitan area. KBS Classic FM, at 93.1 MHz, airs programs such as “Masterful Performances, Masterful Albums.” The range of sounds audible to humans is roughly between 20 Hz and 20 kHz, and the upper limit for high frequencies, in particular, can vary depending on age and individual hearing ability. 20 kHz is a representative upper limit commonly used when describing human hearing. One MHz equals one million hertz, meaning one million periodic oscillations per second. So why, exactly, are such high frequencies used? If you take apart a radio, you’ll find it filled with complex circuits, and it’s not immediately clear what role these circuits play in transforming the radio waves from the broadcast station into the music we hear. In telecommunications engineering, terms like “encoding” and “modulation” are used to explain the principles of communication, but just hearing these words doesn’t give you the slightest clue as to what they mean.
However, if you think of the communication principles behind a radio as simply mimicking the way people converse, you’ll find that the process is actually quite familiar. Now, let’s explore how radio broadcasting works by walking through the process of how people speak and listen.
First, we think of what we want to say in our minds. This “speech” can be described as information existing in the brain that has not yet been converted into sound. To express this verbally, we must first use our vocal cords to produce a voice. However, simply producing a voice does not constitute speech. Only by moving the tongue, lips, and various structures inside the mouth to form pronunciations does it become concrete speech sounds. The movements of the tongue and lips alter the flow of air produced by the mouth and vocal cords, and these changes shape the speech sounds we hear. This process can be seen as transforming the sound produced in the throat into meaningful speech sounds by adding the movements of the tongue and lips.
Radio operates through a similar process. Initially, the music a radio station wants to broadcast exists not as radio waves themselves, but as electrical audio signals. To transmit this signal far beyond the station, high-frequency radio waves must be used. Since the station needs to deliver the signal to numerous radio receivers across a wide area, it does not send the audio signal directly into the air but instead uses radio waves as a medium for transmission. What is used here is a carrier wave with a high frequency measured in MHz. However, it would not be accurate to say that simply because the frequency is high, the radio wave itself becomes a “louder voice” or possesses more energy. The advantage of using a high-frequency carrier wave is that it allows antennas to be built to a practical size and enables different broadcast signals to be assigned to different frequency bands, thereby distinguishing between multiple broadcasts.
Next, the broadcasting station modulates an audio signal—such as music—onto the high-frequency carrier wave. This can be thought of as similar to how a person produces specific speech sounds by combining the sounds generated by the vocal cords with the movements of the tongue and lips. The modulated signal is amplified by the transmitter and then transmitted via the antenna. In communications engineering, the process of embedding the information signal to be transmitted onto a carrier wave is called “modulation.” In AM broadcasting, the amplitude of the carrier wave varies according to the audio signal, while in FM broadcasting, the frequency of the carrier wave varies according to the audio signal. The process of transmitting this modulated signal via radio waves is called broadcasting or transmission.
To summarize, a broadcast station carries the music signal it wishes to transmit onto the carrier wave and transmits it via a transmitter. This process can be compared to how a person conveys thoughts to others using their voice and the movements of their tongue and lips. However, in radio, an electrical audio signal serves as the information instead of a human voice, and the carrier wave acts as the medium for transmitting that information over long distances.
“Speech” leaves the mouth and spreads through the air. Now it is the listener’s turn to hear this speech. To hear the sound, the listener’s auricle and external auditory canal must first collect ambient sounds and transmit them to the eardrum. The sound causes the eardrum to vibrate, and these vibrations are transmitted to the cochlea via the three small bones in the middle ear: the malleus, incus, and stapes. The cochlea is a fluid-filled structure that plays a crucial role in converting the received vibrations into auditory signals. These signals are then transmitted as electrical impulses to the brain via the auditory nerve, where they are recognized as sound. Therefore, human hearing is not simply a process in which the eardrum receives sound; it is a complex process in which vibrations originating in the outer ear pass through the middle and inner ear, are converted into neural signals, and are interpreted by the brain.
Radios follow a similar process. A radio is equipped with an antenna that can receive radio waves transmitted from a broadcast station. The antenna essentially plays a role similar to that of the human outer ear. However, the radio waves received from the broadcast station contain both a carrier wave—which has a high frequency in the MHz range that we cannot hear—and the music signal carried by that carrier wave. For this reason, a device is needed to extract the desired music signal and convert it back into an audio signal that humans can hear.
Have you ever seen a mosaic photo? When viewed up close, it consists of many small, different photos packed tightly together, but when viewed from a distance as a whole, it reveals an entirely different image. You’ve probably seen photos like this before. A radio can be thought of in a similar way—it involves finding the audio signal we want within a complex high-frequency signal. However, an actual radio does not work exactly the same way as simply “viewing the big picture from a distance.” Instead, a circuit analyzes the changes in the signal embedded in the modulated carrier wave to restore the original audio information. The device that extracts the original audio information from the received signal is called a “demodulator,” and the process of finding the original information signal within the composite signal is called “demodulation.”
To summarize the signal reception process: the antenna picks up radio waves; the receiver circuit selects the desired broadcast signal; and the demodulator restores the audio information from the modulated signal. After undergoing the necessary signal processing, the signal is converted into sound that humans can hear. This process can be compared to how the human ear captures sound—the pinna and external auditory canal receive the sound, the eardrum and the small bones of the middle ear transmit the vibrations, and the brain perceives the sound via the cochlea and the auditory nerve.
As shown here, the principles of radio transmission and reception are remarkably similar to the process of human conversation. However, this is not a mere coincidence. In fact, various types of communication that involve the exchange of information fundamentally follow a process of generating information, converting it into a form that can be transmitted, sending it through a transmission medium, and then receiving and restoring it to its original form. In communications engineering, this process is generalized to include the “source (what one wants to say),” “encoding (converting information into a transmissible form),” “transmitter (the device that sends the signal),” “channel (the medium through which the signal is transmitted),” “receiver (the device that receives the signal),” “decoding (the process of restoring the original information from the received signal),” and “destination (the recipient of the information).”
All communication follows this basic process. Communication engineering can ultimately be described as the field that develops technologies to perform each of these steps more accurately and efficiently. Television, the telephone, speaking, and even letters can all be viewed through the lens of communication principles in a broad sense, as they all involve transmitting and receiving information. What is your primary means of communication? Why not try classifying its communication process from a telecommunications engineering perspective? If you have a secret method to improve any one of these steps, you are already viewing the world through the eyes of a telecommunications engineer.
