Sound is a form of energy that travels in waves, and the frequency of these waves determines the pitch a person perceives. Frequency is measured in Hertz (Hz), which represents the number of sound wave cycles that pass a point in one second. A higher frequency registers as a higher pitch. This measurement system is fundamental to understanding how we process auditory information and decode the complex sounds of human language.
The Standard Range of Human Audibility
For a young, healthy human ear, the standard range of hearing spans from approximately 20 Hertz (Hz) to 20,000 Hz (20 kilohertz or kHz). Sounds below 20 Hz are known as infrasound, typically felt as vibration rather than heard. Sounds above 20,000 Hz are classified as ultrasound and are imperceptible to human ears. This extensive range allows us to detect the deep rumble of thunder at the low end and the high-pitched squeak of a bat at the upper limit.
The frequency of a sound directly correlates with its perceived pitch. Low frequencies, such as those produced by a tuba, are perceived as deep, resonant tones. Conversely, high frequencies, like the sounds of a whistle, produce sharp, treble tones. The most significant part of the frequency spectrum is dedicated to speech.
The frequency range most important for human communication is the “speech banana,” a cluster of sounds between roughly 250 Hz and 8,000 Hz. Lower frequencies primarily contain vowel sounds, which contribute to the loudness of speech. Higher frequencies contain most consonants (e.g., ‘s’, ‘f’, and ‘th’), which are necessary for speech clarity and word recognition.
How Age and Noise Exposure Change Frequency Perception
While the 20 Hz to 20,000 Hz range is the theoretical maximum, an individual’s actual hearing ability changes significantly over time due to two primary factors. The first is presbycusis, the gradual hearing loss that occurs as a person ages. This decline is symmetrical and starts by affecting the highest frequencies first.
The ability to hear frequencies above 8,000 Hz may begin to diminish even in young adulthood, and this high-frequency loss progresses to affect lower tones over decades. This age-related change is caused by the deterioration of the hair cells (stereocilia) within the inner ear’s cochlea, which do not regenerate once damaged. The early loss of high-frequency sensitivity means people first struggle with sounds like birdsong before noticing difficulty with speech itself.
The second major cause is Noise-Induced Hearing Loss (NIHL), resulting from acute or prolonged exposure to loud sounds. NIHL physically damages the delicate hair cells in the cochlea, leading to permanent hearing loss. This damage creates a pronounced dip, known as an audiometric notch, centered around the 4,000 Hz frequency.
The ear’s anatomy contributes to this vulnerability at 4,000 Hz because the external ear canal acts as a resonator, amplifying sound energy at this frequency. This amplification causes disproportionate mechanical stress and damage to the basilar membrane in the inner ear. Although the initial loss is localized at 4,000 Hz, continued loud noise exposure causes the damage to deepen and widen, encroaching upon the lower speech frequencies.
Methods Used to Measure Hearing Frequency
To quantify a person’s hearing ability across the frequency spectrum, an audiologist performs a pure-tone hearing test. The results are plotted on a specialized graph called an audiogram. This visual tool uses the horizontal axis to represent frequency, measured at octaves (doublings of sound), such as 250 Hz, 500 Hz, 1,000 Hz, 2,000 Hz, 4,000 Hz, and 8,000 Hz.
The goal is to determine the hearing threshold for each frequency—the softest level of sound a person can detect at least 50% of the time. This threshold is plotted on the audiogram’s vertical axis in decibels (dB), indicating the intensity or loudness of the sound. A person with typical hearing has thresholds that cluster near the top of the graph. A lower position on the chart indicates a reduced ability to hear that pitch. The audiogram maps an individual’s hearing profile, showing where perception deviates from the standard range.