I have completed writing the entire script. However, it might exceed 10 minutes in length, so I plan to record it first and then shorten it by removing parts that can be omitted if necessary.

Chapter 1: The Universal Definition of Sound

What is sound?

Sound is the transmission of pressure waves emitted from a sound source through a medium. From a physical perspective, defining sound seems straightforward.

But is this all there is to sound?

Chapter 2: Exceptions to the Universal Definition of Sound

Let’s try something. Here’s an audio track. Raise your hand when you can no longer hear the sound.

(Sound: A tone gradually increasing from 50Hz to 20,000Hz)

Most people’s cut-off point will be similar but not exactly the same. What you just heard is an audio track with steadily increasing frequency, starting from 50Hz. While human hearing is generally said to range from 20Hz to 20,000Hz, most people detect sounds between 35Hz and 17,000Hz. So, if a tone at 18,000Hz is audible to some but not others, can it still be called a sound?

Moreover, what about infrasound (below 20Hz) and ultrasound (above 20,000Hz)—pressure waves that exist physically but cannot be heard by humans? Can we define these as sound?

Here’s another example, slightly different. Imagine an elephant in your mind. Now picture the sound of that elephant being pierced by a spear.

(Sound: An imitation of an elephant’s death cry)

This is roughly the sound I imagined. Whatever sound you thought of, the key point is that you “heard” the elephant’s death cry in your mind. This sound has no physical vibration, yet we perceive it. Don’t think this counts as hearing because the sound isn’t vivid enough? Consider this:

(Sound: A high-frequency tone gradually increasing in volume from the left speaker)

This is tinnitus. While the sound here is artificially generated, many people have experienced tinnitus at some point. Tinnitus can arise when hair cells in the cochlea are damaged by loud noises, prompting the brain to compensate by perceiving phantom sounds. Another possible cause is vascular constriction triggered by autonomic nervous system responses.

Regardless of the exact mechanism, what’s clear is this: humans can perceive auditory information even without physical vibrations. Can we still call these phenomena “sounds”?

Chapter 3: Redefining Sound

For someone experiencing tinnitus, they might say, “What I’m hearing right now is definitely a sound.” But if no one else can hear it, can we truly call it a sound? Similarly, if a high-frequency sound at 18,000Hz is audible to one person but not another, how can we universally define it as sound?

In this way, sound is inherently personal, sensory, and subjective. However, O’Callaghan Casey, in his journal Auditory Perception, argues against the notion that sound is purely subjective:

“However, the claim that sounds are sensations is unattractive. Good reasons suggest that sounds are public rather than private, even if sounds are not identical with ordinary objects and events such as clothespins and collisions. Suppose I am near the stage in a hall listening to some music, and that I have a headache. It is a confusion to think you could feel my headache, but I assume you hear the sounds I hear. Suppose I move to the back of the hall, and the headache then gets better. My experience of the sounds of the music differs once I am at the back of the room, and my experience of the headache differs. The sound of the music itself need not differ (the musicians could make the same sounds), but the headache itself changes.”

Even O’Callaghan, however, implicitly acknowledges sound’s subjective nature by assuming others hear the same sounds as he does. Differences in ear structure, eardrum condition, and the physical vibrations reaching the ear—based on one’s seating position—mean that no two people hear sounds identically. Yet, it is true that most people perceive similar sounds.

In this way, sound is deeply personal while also possessing a shared universality. Humans process auditory information subjectively, regardless of whether physical vibrations exist.

Chapter 4: The Uncertainty of Auditory Perception

Humans don’t analyze every element of sound in real time; instead, they rely on prediction. The famous McGurk Effect illustrates this phenomenon. This is an intriguing example of cross-modal sensory integration, where visual information influences auditory perception, leading people to hear something different from the actual sound.

For instance, if a video of someone saying “/ga/” is dubbed with audio of “/ba/,” people perceive the sound as “/da/.” While such cross-modal illusions occur, many auditory illusions arise purely from auditory information itself.

Chapter 5: Examples of Auditory Illusions

(Sound: Endless staircase music from Super Mario 64)

This is an example of the Shepard Tone, an auditory illusion where overlapping tones from multiple octaves give the impression of infinite rising or descending pitch. In reality, the pitch cycles back. This effect is often used in games, films, and music to build tension—for example, in Radiohead’s Burn the Witch and Hans Zimmer’s Why So Serious from The Dark Knight.

(Sound: Speech intermittently cutting out)

Notice the gaps in the speech?

(Sound: Same speech with background noise masking the gaps)

How about now? Did it sound smoother?

The original audio actually sounds like this:

(Sound: Speech without the masking sounds)

This phenomenon, called the Auditory Continuity Illusion, occurs when the brain fills in gaps, perceiving a continuous sound even when parts are missing.

Finally, consider this cultural example. Listen to these two tones and decide if the pitch ascends or descends:

(Sound: Tritone Paradox example)

The Tritone Paradox, discovered by Diana Deutsch, demonstrates how different listeners perceive the same tones as ascending or descending based on their cultural or linguistic background.

Chapter 6: The Importance of Recognizing Subjectivity in Sound

Until now, discussions of sensory illusions have primarily focused on vision, shaping philosophical frameworks like idealism around visual perception. The other senses—hearing, smell, touch, and taste—have received far less philosophical attention.

Philosopher Lycan argued that if philosophy had centered on olfaction, it would have developed in an entirely different direction. Similarly, a deeper exploration of auditory perception could yield novel concepts, akin to inventing new musical instruments.

In the mid-20th century, such questions about the nature of sound and music spurred innovations like musique concrète, experimental music, avant-garde music, and electronic music. Philosophical inquiries into “What is sound?” and “What do we hear?” opened new artistic frontiers.

By acknowledging the subjectivity of sound, artists can unlock boundless creative possibilities.

Chapter 7: Interview with Musician WonWoo Lee

Interviewer: Hello, Composer WonWoo Lee. Thank you for taking the time to speak with me despite your busy schedule.

WonWoo Lee: Hello. My name is WonWoo Lee, and I currently work under the name WonWoo Lee. I’m a lecturer at the Korea National University of Arts, and I create music specifically for cochlear implant users.

Interviewer: Could you explain what a cochlear implant is?

WonWoo Lee: A cochlear implant is a medical device that has been in use for about 30 years, developed in countries like Australia and the United States to assist individuals with hearing impairments. Unlike hearing aids that amplify sound, cochlear implants use a SUS (Suspended or Sustained Stimulus) mechanism. Electrodes are implanted in the cochlea, and an external microphone captures sound, converting it into electrical signals that are directly transmitted to the cochlea. Typically, these implants have around 12 to 20 electrodes, each responding to a specific frequency, enabling users to distinguish between frequencies.

Interviewer: I’ve heard that cochlear implant users hear sounds quite differently from individuals with normal hearing. Is that correct?

WonWoo Lee: Yes, that’s true. The human cochlea typically contains about 3,000 hair cells, which enable us to distinguish a wide range of frequencies. Cochlear implants, however, only have 12 to 20 electrodes. This makes it much harder for implant users to distinguish frequencies with the same sensitivity as natural cochlear hair cells. In fact, research suggests that increasing the number of electrodes for more detailed frequency distinction might result in users hearing more “noise”—unnecessary sounds—which makes it even harder to perceive desired sounds clearly.

Here’s an example of what sound might be like for cochlear implant users. Take a listen.

(Sound: News audio as perceived by cochlear implant users)

Interviewer: Wow, it sounds much more mechanical than I expected. Honestly, I can barely make out what’s being said.

WonWoo Lee: Right, but with training, most people adapt to speech over time. For instance, if you listen to the original version of that audio and then compare it to the version perceived by cochlear implant users, you’ll notice it becomes easier to understand. Let’s try it.

(Sound: Original news audio / Cochlear implant user’s version)

Interviewer: Oh, I see what you mean. It’s much clearer now.

WonWoo Lee: Humans don’t process sound entirely in real time; they predict and interpret it as they listen. That’s why cochlear implant users can generally adapt to speech after about a year of use, as speech follows relatively consistent grammatical patterns. However, music is a different story. Each composer’s musical language is unique, and unlike speech, which focuses on meaning, music requires direct perception of sound itself. This presents a much greater challenge. Let’s listen to the same comparison, but this time with music.

(Sound: Processed music / Original music / Processed music again)

Interviewer: The processed version sounds entirely different from the original. It even feels like modern experimental music. But unlike speech, even after hearing the original, I still can’t quite grasp the processed version.

WonWoo Lee: Exactly. That realization made me reflect on why I had assumed everyone hears the same sounds I do. This prompted me to create music specifically designed for cochlear implant users.

Interviewer: How is music for cochlear implant users different?

WonWoo Lee: First, they have difficulty distinguishing frequencies such as “Do” and “Mi,” which might sound almost identical. To address this, melodies often involve leaps to make them more distinguishable. Rhythms tend to be simpler, and sounds with short sustain—like percussion—are easier for them to perceive. Additionally, too much reverb creates lingering noise, making it harder for users to discern sounds, so we minimize reverb as much as possible.

These compositions can serve both as enjoyable music and as tools for rehabilitation, helping users become accustomed to specific frequencies. I’m also currently working on developing an application that compiles these pieces.

Interviewer: Thank you for sharing that. Lastly, could you tell us what “sound” means to you?

WonWoo Lee: To me, sound is something unstructured within the flow of time. When it gains structure, it becomes music.

Interviewer: That’s a profound and unique definition. My current project explores the subjectivity of sound perception. Do you believe sound inherently has subjective characteristics?

WonWoo Lee: Absolutely. For instance, I personally can’t hear sounds above 15,000Hz, so whenever I mix music, my high frequencies tend to be overly pronounced. From physical processes to cognitive perception, everyone processes sound differently. Cochlear implant users are an extreme example of this variability. Sound is, without a doubt, subjective.

Chapter 8: Conclusion

This exploration demonstrates that sound is inherently personal and subjective. From auditory illusions to the unique experiences of cochlear implant users, we see that perception is uncertain and varies between individuals.

As artists, how will we respond to this and incorporate it into our creative worlds? The possibilities are endless.