Hearing, Pitch and Loudness
In 1876, Francis Galton invented a whistle producing 40,000 Hz — far beyond the 20,000 Hz human ceiling, but easily heard by his test dogs.
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Q1 · Why do you think some people lose the ability to hear high-pitched sounds as they get older?
Q2 · A dog whistle makes a sound your dog reacts to but you cannot hear. What does this tell you about the frequency of the whistle compared to your hearing range?
● Know
- Pitch is determined by the frequency of a sound wave.
- Loudness is determined by the amplitude of a sound wave.
- The human ear detects vibrations and converts them into electrical signals sent to the brain.
● Understand
- The structure of the ear is adapted to collect, amplify, and process sound vibrations.
● Can do
- Relate changes in pitch and loudness to changes in frequency and amplitude.
If you have ever been in a room with an old CRT television — even with the sound turned off — you may have heard a faint high-pitched whine around 15,750 Hz that nobody over 40 seemed to notice. That gap in perception is direct evidence of how hearing range changes with age. For healthy young humans, the hearing range spans roughly 20 Hz to 20,000 Hz. As we age, the upper limit drops, often to around 12,000–15,000 Hz by middle age.
Other animals have evolved very different ranges depending on their needs. Dogs hear up to about 45,000 Hz, which is why dog whistles are inaudible to us. Bats and dolphins hear well above 100,000 Hz, using ultrasound for echolocation and navigation. Elephants communicate with infrasound below 20 Hz, allowing them to send messages over distances of several kilometres.
The hearing range depends on the anatomy of the ear. The cochlea contains hair cells of different lengths, each sensitive to a specific frequency range. High-frequency sounds stimulate hair cells near the entrance; low frequencies stimulate cells deeper inside. Damage to these hair cells, from ageing or loud noise, reduces the hearing range.
A 15-year-old might hear a 17,000 Hz tone clearly, while their 50-year-old teacher hears nothing. This is not because the teenager has better concentration; it is because the teacher cochlear hair cells for high frequencies have been damaged or lost over time. The sound wave is identical; the difference is in the detector.
Australian veterinary science: Australian veterinarians use knowledge of animal hearing ranges to design less stressful environments. Kennels avoid high-frequency equipment that distresses dogs. Wildlife researchers use infrasound playback to study elephant communication in African reserves, applying the same principles that apply to Australian native species.
If I cannot hear a sound, it must be too quiet. Inaudibility can mean either too quiet (low amplitude) or too high or low in frequency (outside hearing range). A dog whistle is inaudible not because it is quiet, but because its frequency is above 20,000 Hz. Your ear simply cannot detect it, no matter how loud it becomes.
- Human
- Dog
- Bat
- Elephant
- Dolphin
- 20 Hz to 20 kHz
- Up to 45 kHz
- Up to 150 kHz
- Up to 120 kHz
- Down to 14 Hz
Pitch is the subjective experience of frequency. When more compressions reach your ear each second, your brain interprets the sound as higher in pitch. When fewer compressions arrive, you hear a lower pitch. This relationship is direct and reliable: double the frequency, double the perceived pitch (one octave higher).
The human ear is remarkably sensitive to pitch differences. Trained musicians can distinguish frequencies that differ by less than 1%. This sensitivity arises because the cochlea mechanically separates frequencies along its length, sending precise signals to the brain about which hair cells are stimulated.
Pitch is not loudness. A flute playing a high note softly has high frequency but low amplitude. A tuba playing a low note loudly has low frequency but high amplitude. Your brain processes these two dimensions independently, allowing you to perceive both the note and its volume simultaneously.
When a siren approaches, the pitch sounds higher than when it moves away. This is the Doppler effect: the motion of the source compresses the waves in front and stretches them behind. The frequency reaching your ear increases as the siren approaches and decreases as it recedes. The actual siren frequency has not changed; only your received frequency has.
Australian magpie songs: Australian magpies produce some of the most complex bird songs, with frequency modulations spanning several kilohertz. Researchers at the Australian National University analyse these songs to understand how birds learn and remember complex sound patterns. The pitch variations encode information about the bird identity and territorial claims.
High-pitched sounds travel faster than low-pitched sounds. In a given medium, all sound waves travel at the same speed regardless of frequency. A high-pitched whistle and a low-pitched drum reach you at the same time if they start together. The difference is in frequency, not speed. If pitch affected speed, orchestras would sound chaotic as different notes arrived at different times.
Loudness is the perceived intensity of a sound, and it is determined by amplitude. A sound wave with large amplitude has compressions that are much more compressed and rarefactions that are much more spread out. These stronger pressure variations push your eardrum further, and your brain interprets this as louder sound.
The relationship between amplitude and loudness is not linear. Because the ear responds logarithmically, doubling the amplitude does not double the perceived loudness. It increases it by a smaller amount. This is why the decibel scale is logarithmic: each 10 dB increase represents a tenfold increase in intensity, but only a doubling of perceived loudness.
Amplitude and frequency are completely independent. You can change one without affecting the other. Shouting a high note increases amplitude but keeps frequency the same. Whispering a low note decreases amplitude but keeps frequency the same. Understanding this independence is essential for music, engineering and hearing protection.
A microphone converts sound waves into electrical signals. When you sing softly, the microphone diaphragm moves a tiny distance and produces a small electrical voltage. When you sing loudly, the diaphragm moves much further and produces a larger voltage. The frequency of the electrical signal matches the frequency of your voice; only the amplitude changes. This is how recording equipment captures both pitch and loudness separately.
Australian aviation noise limits: Airservices Australia monitors aircraft noise around airports using decibel measurements. A jet taking off produces sound at about 140 dB near the engine, enough to cause immediate hearing damage. Regulations require noise-abatement procedures and insulation for homes under flight paths. These rules depend on accurate measurement of sound amplitude.
Louder sounds have higher frequencies. This confusion arises because some high-frequency sounds, like screams, are often loud. But consider a whispered squeak (high frequency, low amplitude) and a shouted bass note (low frequency, high amplitude). Frequency and amplitude are separate dials on the sound mixer, not linked levers.
Pitch and loudness are the two most obvious properties of a sound, but they correspond to completely different physical quantities. Pitch is frequency. Loudness is amplitude. Keeping them separate in your mind is essential for understanding sound, music and hearing.
On a sound mixer or music production software, you control pitch and loudness with separate controls. A graphic equaliser adjusts amplitude at different frequencies independently. You can boost the bass (low frequencies) while cutting the treble (high frequencies), or make everything louder without changing the relative balance of frequencies.
Your ear and brain also process these properties separately. Different neural pathways carry pitch and loudness information from the cochlea to the auditory cortex. This is why hearing loss can affect one property more than the other. Some people lose sensitivity to high frequencies (affecting pitch perception) while maintaining normal loudness perception. Others lose overall sensitivity (affecting loudness) across all frequencies.
When a DJ plays a track, they might turn up the bass using the low-frequency knob. This increases the amplitude of low frequencies without changing their pitch. They might also adjust the tempo, which changes the playback speed and therefore shifts all frequencies up or down. Changing tempo affects pitch; changing the equaliser affects loudness. Good DJs understand the difference.
Australian music education: The Australian Music Examinations Board tests students on their ability to distinguish pitch and loudness changes in recorded excerpts. This aural skill underpins all musical training. Understanding the physics behind these perceptions helps students articulate why a performance sounds different when dynamics or tuning change.
If a sound gets louder, it also gets higher in pitch. This is called the missing fundamental illusion in reverse. Some people conflate loudness and pitch because both are perceived as more intense. But physically and perceptually, they are independent. A note can be loud and low, quiet and high, or any other combination.
Sort each description to the correct property.
Hearing is not static. It changes throughout life, primarily due to two factors: ageing and noise exposure. As we get older, hair cells in the cochlea gradually die and are not replaced. High-frequency hair cells are usually affected first, which is why older people often struggle to hear consonants in speech or high-pitched alarms.
Noise-induced hearing loss is caused by prolonged or intense exposure to loud sounds. Sounds above 85 dB can cause damage with extended exposure. Sounds above 120 dB can cause immediate damage. Concerts, power tools, firearms and even some personal music players at maximum volume can exceed these thresholds.
Protection is simple but effective. Earplugs reduce sound intensity by 15-30 dB. Limiting exposure time gives hair cells a chance to recover. Regular hearing tests, especially for musicians and industrial workers, catch problems early before they become permanent. Once hair cells are destroyed, they do not regenerate.
A construction worker uses a jackhammer producing 110 dB. Without protection, they exceed safe daily exposure in under two minutes. With earmuffs rated at 25 dB reduction, the effective level is 85 dB, allowing about eight hours of safe exposure. The earmuffs do not block all sound; they reduce amplitude enough to prevent damage while still allowing communication.
Australian hearing standards: Safe Work Australia mandates hearing conservation programs for noisy workplaces. The National Acoustic Laboratories in Sydney research hearing loss prevention and develop testing protocols. Australian standards for ear protection are among the strictest in the world, reflecting the high prevalence of industrial and recreational noise exposure.
Only very loud sounds damage hearing. Prolonged exposure to moderately loud sounds (85-95 dB) causes cumulative damage over years. A nightclub at 95 dB damages hearing in about one hour. Riding a motorbike at 90 dB for a full day causes significant stress to hair cells. Damage is about both level and duration.
As people , they often lose the ability to hear frequencies. This is why some can hear high-pitched ringtones that adults cannot.
The distinction between pitch and loudness is not just academic; it is essential for music, communication and technology. Musicians must control both properties simultaneously. Engineers must design systems that reproduce both accurately. Doctors must diagnose hearing problems that affect one property but not the other.
In music, dynamics refer to loudness (piano for soft, forte for loud). Melody and harmony refer to pitch relationships. A composer might write a passage that is both high in pitch and soft in loudness, or low in pitch and loud. These combinations create the emotional texture of music.
In speech, pitch variations carry meaning (intonation). Loudness variations carry emphasis. A whispered warning and a shouted warning have the same words but completely different communicative effects. Understanding that these are controlled by independent wave properties helps us analyse how speech conveys information beyond the literal meaning of words.
A hearing aid must amplify sounds without distorting pitch. If it boosted amplitude unevenly across frequencies, some notes would become disproportionately loud, making music sound harsh and speech hard to understand. Modern digital hearing aids use multiple frequency bands, adjusting loudness independently for each band to preserve the natural pitch relationships the wearer needs to understand speech in noisy environments.
Cochlear implants in Australia: Australian researchers at the Bionics Institute in Melbourne developed early cochlear implant technology. These devices bypass damaged parts of the ear and directly stimulate the auditory nerve with electrical signals. Engineers must carefully encode both frequency (pitch) and intensity (loudness) information into these signals so that users can understand speech and appreciate music.
Pitch and loudness are just two ways of saying the same thing. They are as different as colour and brightness for light. A red light can be bright or dim; a high note can be loud or soft. Just as you would never confuse colour with brightness, you should never confuse pitch with loudness. They are independent dimensions of sound.
You learned that pitch depends on frequency and loudness depends on amplitude, and how the ear detects sound.
Why can some animals (like dogs) hear sounds that humans cannot? What does this tell you about the frequency range of dog hearing compared to humans?
The hook described how dogs hear up to 65 000 Hz — well beyond your 20 000 Hz limit — which is why a dog whistle is completely silent to you yet sends your dog running.
Now that you've studied pitch, loudness, frequency and amplitude properly, how would you explain what your brain is actually doing when you perceive a high-pitched sound versus a loud one? Did the dog whistle example change how you thought about hearing?
1. What property of a sound wave determines its pitch?
2. What happens to the loudness of a sound if its amplitude is doubled?
3. Which part of the ear converts vibrations into electrical signals?
4. The typical human hearing range is:
5. A singer sings a note and then sings the same note more loudly. Which wave property has changed?
Describe the journey of a sound wave from the air to the brain, naming the main parts of the ear involved. (3 marks)
Hint: Include the outer ear, eardrum, ossicles, cochlea, and auditory nerve.
Explain the difference between pitch and loudness, and identify which wave property is responsible for each. (3 marks)
Hint: Use the terms frequency and amplitude in your answer.
A student claims that a high-pitched sound must also be loud. Explain why this statement is incorrect, using examples. (3 marks)
Hint: Think of examples where pitch and loudness do not match the student's claim.