Audio frequency is any vibration in the air that the human ear can detect, ranging from 20 Hz to 20,000 Hz (20 kHz). Hertz (Hz) measures how many times a sound wave completes a full cycle per second. A low-pitched hum like a bass guitar vibrates slowly, around 80 to 100 times per second, while a high-pitched whistle might vibrate 4,000 times per second or more. Everything you hear falls somewhere on this spectrum.
How Frequency Relates to Pitch
Frequency and pitch are closely linked but not identical. Frequency is a physical measurement of vibrations per second. Pitch is your brain’s interpretation of those vibrations. When frequency doubles, you perceive the pitch rising by one octave. So a note at 440 Hz (the standard tuning note for orchestras worldwide, known as A4) sounds exactly one octave higher than the same note at 220 Hz.
The relationship between frequency and the physical size of a sound wave is straightforward: speed equals frequency times wavelength. Sound travels through air at roughly 343 meters per second at room temperature. A 20 Hz bass note has a wavelength of about 17 meters, which is why low frequencies can bend around walls and travel through buildings. A 20,000 Hz tone has a wavelength of just 1.7 centimeters, making it highly directional and easy to block.
The Audio Frequency Spectrum
Not all frequencies within the 20–20,000 Hz range sound or behave the same way. Audio engineers and musicians divide the spectrum into distinct bands, each with a recognizable character:
- Sub-bass (20–60 Hz): More felt than heard. These are the deep rumbles in movie theaters and the chest-thumping lows from subwoofers.
- Bass (60–250 Hz): The foundation of music. Kick drums, bass guitars, and the lower notes of a male voice live here.
- Lower midrange (250–500 Hz): Adds warmth and body to vocals and instruments. Too much energy here makes audio sound muddy.
- Midrange (500 Hz–2 kHz): The most important range for understanding speech. Human ears are naturally more sensitive in this region.
- Upper midrange (2–4 kHz): Where the ear is at peak sensitivity. Consonants in speech, the attack of a snare drum, and the bite of an electric guitar sit in this range.
- Presence (4–6 kHz): Gives audio a sense of clarity and closeness.
- Brilliance (6–20 kHz): The shimmer of cymbals, the sibilance in vocals, and the “air” that makes a recording feel open and spacious.
How Your Ear Separates Frequencies
Deep inside your inner ear, a snail-shaped structure called the cochlea does the work of splitting sound into its individual frequencies. It contains a thin strip of tissue called the basilar membrane that vibrates in response to incoming sound. This membrane is not uniform. It’s stiff and narrow at the base (near the entrance) and wide and flexible at the tip.
High-frequency sounds cause the greatest vibration near the base of the cochlea, while low-frequency sounds travel further along and produce the largest vibrations near the tip. This physical sorting system, first demonstrated by Nobel Prize-winning physicist Georg von Békésy in experiments during the 1940s, means that each spot along the membrane responds best to a specific frequency. Tiny hair cells sitting on the membrane convert those vibrations into electrical signals that travel to the brain, where you perceive them as distinct pitches.
Why You Lose High Frequencies With Age
The 20–20,000 Hz range describes the theoretical maximum for human hearing. In practice, most adults can’t hear anywhere near 20,000 Hz. Infants can detect frequencies slightly above 20 kHz, but the upper limit drops steadily with age. The average adult tops out around 15,000 to 17,000 Hz.
The decline is steepest at the highest frequencies. Research measuring hearing thresholds across age groups shows the difference clearly. Adults under 30 can typically hear 16,000 Hz at very soft volumes. By the 40s, it takes a significantly louder signal to detect that same 16,000 Hz tone. By the late 50s and into the 60s, 16,000 Hz requires the sound to be cranked up to roughly 65 decibels, about the volume of a normal conversation, before it’s even detectable. Frequencies above 12,500 Hz become increasingly difficult to hear past age 50, with thresholds climbing steeply.
This gradual loss, called presbycusis, happens because the delicate hair cells in the cochlea wear out over a lifetime. The cells responsible for high frequencies sit near the base of the cochlea, where sound enters first, so they take the most cumulative damage from noise exposure.
Audio Frequency in Digital Sound
When sound is recorded digitally, a microphone captures the analog sound wave and a converter measures (samples) its amplitude thousands of times per second. The standard sampling rate for CDs and most digital music is 44,100 samples per second (44.1 kHz). That number isn’t arbitrary.
A principle called the Nyquist theorem states that to accurately capture a given frequency, you need to sample at least twice per cycle. So a 44.1 kHz sampling rate can faithfully reproduce frequencies up to 22,050 Hz, comfortably above the 20,000 Hz ceiling of human hearing. Higher sampling rates like 48 kHz (standard for video) and 96 kHz (used in some studio recordings) provide extra headroom that helps with audio processing, but they don’t capture sounds that human ears can actually hear.
Frequencies Beyond Human Hearing
Sound doesn’t stop existing below 20 Hz or above 20 kHz. It simply falls outside what humans can perceive. Sounds below 20 Hz are called infrasound, and sounds above 20 kHz are called ultrasound. Many animals operate comfortably in these ranges.
Dogs can hear up to about 46 kHz, which is why a dog whistle (typically pitched around 23–35 kHz) is inaudible to you but perfectly clear to your pet. Mice hear up to 100 kHz. Rats detect frequencies up to 76 kHz. Even nonhuman primates like rhesus monkeys hear up to 45 kHz, more than double the human ceiling.
Infrasound is produced by earthquakes, ocean waves, wind turbines, and large industrial equipment. At low intensities, it’s simply imperceptible. At high intensities (above 100 decibels), infrasound can produce real physiological effects. Reported symptoms from chronic exposure include headaches, fatigue, dizziness, difficulty concentrating, and mood changes. Lab research has shown that exposure to high-level infrasound above 100 decibels can interfere with heart muscle contractility, reducing the force of contraction by roughly 11% at 110 decibels and 18% at 120 decibels. The frequency of 10 Hz appears to produce the most pronounced cardiac effects.
Musical Tuning and Reference Frequencies
The most famous single audio frequency is probably 440 Hz, the international standard pitch for tuning musical instruments, formalized by the International Organization for Standardization as ISO 16. When an orchestra tunes up before a concert, the oboe plays an A at 440 Hz and every other instrument matches it.
This standard wasn’t always universal. Before 440 Hz was adopted, many countries followed the French standard of 435 Hz, established in the 1860s. Even today, the standard flexes. European orchestras commonly tune between 440 and 444 Hz for a brighter sound. Leonard Bernstein regularly tuned the New York Philharmonic to 442 Hz, which reportedly drew complaints from piano tuners. Musicians playing historical instruments on period-accurate terms often tune to 415 Hz for baroque music or as high as 466 Hz for certain German church compositions from Bach’s era.