Human Perception of Sound
Introduction
Sound waves have physical properties such as frequency, amplitude, wavelength, time period and speed. These properties can be measured.
But the way we experience sound is called human perception of sound. It is described mainly by terms such as pitch and loudness.
For example, a whistle sounds sharp, thunder sounds deep, a soft voice sounds gentle and a firecracker sounds very loud. These experiences depend on how our ears and brain receive and understand sound waves.
What is Human Perception of Sound?
Human perception of sound means the way humans hear, feel and identify different sounds.
A sound wave reaches our ear as a disturbance in air. The ear changes this disturbance into signals, and the brain understands these signals as sound.
How Do We Hear Sound?
When sound enters the ear, it makes a thin membrane called the eardrum vibrate. These vibrations are amplified by tiny bones in the ear. Then the cochlea converts the vibrations into electrical signals. These signals go to the brain, and the brain perceives them as sound.
Pitch of Sound
Pitch is the way humans perceive the frequency of sound.
A sound with high frequency is usually heard as a high-pitched or shrill sound. A sound with low frequency is usually heard as a low-pitched or deep sound.
Examples of High and Low Pitch
| Type of Sound | Perception | Example |
|---|---|---|
| High frequency sound | High pitch / Shrill sound | Whistle, siren |
| Low frequency sound | Low pitch / Deep sound | Thunder, aircraft rumble |
In general:
- Higher frequency produces higher pitch.
- Lower frequency produces lower pitch.
- The exact relation between frequency and pitch is not very simple because perception also depends on the listener.
Why Do Different Voices Sound Different?
Every person’s voice sounds unique. We can often recognise our teachers, friends or family members just by hearing their voice.
Voices differ because they are affected by:
- frequency of vibration of vocal cords,
- shape of the throat,
- shape of the mouth,
- nasal cavity.
During adolescence, boys’ vocal cords become longer and thicker. They vibrate less frequently, so the voice becomes deeper.
Audible Range of Human Hearing
Humans cannot hear all sounds. We can hear only a limited range of frequencies. This range is called the audible range or human hearing range.
Human hearing range = 20 Hz to 20,000 Hz
The upper limit \(20,000\,Hz\) is also written as \(20\,kHz\).
This range may vary from person to person. It also decreases with age.
Infrasonic and Ultrasonic Waves
Sounds below and above the human hearing range cannot be heard by humans.
| Type of Sound Wave | Frequency Range | Can Humans Hear? | Examples of Animals |
|---|---|---|---|
| Infrasonic waves | Below \(20\,Hz\) | No | Elephants can detect infrasound |
| Audible sound | \(20\,Hz\) to \(20,000\,Hz\) | Yes | Humans hear in this range |
| Ultrasonic waves | Above \(20\,kHz\) | No | Dogs, cats, bats and dolphins can detect ultrasound |
Loudness of Sound
Loudness is the way humans perceive the amplitude of a sound wave.
A sound wave with larger amplitude is heard as a louder sound. A sound wave with smaller amplitude is heard as a softer sound.
Larger amplitude → Louder sound
Smaller amplitude → Softer sound
The loudness of sound decreases when we move farther away from the source.
Loudness and Intensity
In daily language, loudness and intensity are often used in the same way. But scientifically, they are not exactly the same.
| Term | Meaning |
|---|---|
| Intensity | It is a measurable physical quantity related to sound energy. |
| Loudness | It is the perception of sound and depends on the listener’s hearing ability. |
Decibel Scale
Sound loudness is commonly measured in decibels, written as dB.
| Sound | Approximate Loudness |
|---|---|
| Rustling leaves | A few dB |
| Normal conversation | About \(60\,dB\) |
| Very loud sounds such as firecrackers | Can exceed \(100\,dB\) |
Even a small increase in decibel level means a large increase in sound intensity.
Noise and Noise Pollution
Unwanted or harmful sound is called noise.
Noise pollution is a serious problem. Exposure to loud sound for a long time can affect:
- health,
- sleep,
- hearing ability.
Prolonged exposure to loud sounds may lead to hearing loss. Hearing loss can be tested using audiograms.
Hearing Aid
People with hearing loss may use a hearing aid. A hearing aid helps the wearer hear and communicate better.
A hearing aid mainly contains:
- Microphone — receives sound,
- Amplifier — increases the electrical signal,
- Speaker — sends sound to the ear.
Why Do We Have Two Ears?
Having two ears helps the brain identify the direction from which sound is coming.
If a sound comes from one side, it reaches the nearer ear slightly earlier than the other ear. The brain compares this tiny time gap and understands the direction of the sound source.
Animal Hearing
Different animals hear in different ways.
- Dogs, cats, bats and dolphins can detect ultrasound.
- Elephants can detect infrasound.
- Snakes and fish sense vibrations through their bodies.
- Some insects have ear-like organs on their body parts.
Important Terms
1. Human Perception of Sound
The way humans hear and experience sound is called human perception of sound.
2. Pitch
Pitch is the perception of frequency of sound.
3. Loudness
Loudness is the perception of amplitude of sound.
4. Audible Range
The range of frequencies that humans can hear is called the audible range.
5. Infrasonic Waves
Sound waves with frequency below \(20\,Hz\) are called infrasonic waves.
6. Ultrasonic Waves
Sound waves with frequency above \(20\,kHz\) are called ultrasonic waves.
7. Noise
Unwanted or harmful sound is called noise.
8. Decibel
Decibel, written as dB, is commonly used to measure sound loudness.
Important Points
- Sound has measurable properties such as frequency, amplitude, wavelength, time period and speed.
- Human perception of sound is subjective and depends on how the ear and brain receive sound.
- Pitch is related to frequency.
- High frequency sounds are generally high-pitched.
- Low frequency sounds are generally low-pitched.
- Loudness is related to amplitude.
- Larger amplitude produces louder sound.
- The human hearing range is from \(20\,Hz\) to \(20,000\,Hz\).
- Sounds below \(20\,Hz\) are infrasonic waves.
- Sounds above \(20\,kHz\) are ultrasonic waves.
- Unwanted or harmful sound is called noise.
- Long exposure to loud sound can damage hearing.
- Two ears help us identify the direction of sound.
Conclusion
Human perception of sound explains how we hear and understand different sounds. The frequency of a sound wave is perceived as pitch, while its amplitude is perceived as loudness. Humans can hear sounds only in the range of about \(20\,Hz\) to \(20,000\,Hz\). Sounds outside this range are not heard by humans, although some animals can detect them. Our ears and brain work together to help us hear, recognise voices, judge loudness and find the direction of sound.
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