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Low Frequencies
The sound of drums, thunder and explosions have low-frequency sound vibrations between about 20 Hz and 200 Hz. These sounds are non-directional, meaning, because of the way your hearing works, it is difficult to pinpoint the sound's location. You cannot hear pure sine waves under 20 Hz -- though, if they're powerful enough, you may feel them in your body. You hear more complex waves, such as that of a ticking sound, under 20 Hz, because you hear the high-frequency harmonics of the sound, not the base frequency. When sped up to 20 Hz, you no longer hear the sound as individual "ticks" -- the sound becomes a low buzzing tone.
High Frequencies
Most people under the age of 40 can hear high frequencies ranging from 10,000 Hz to 20,000 Hz. Above this, the sound becomes inaudible to humans. This is true regardless of the complexity of the tone, because any overtones have yet higher frequencies. The recording frequency of data on a compact disc, or CD, is 44,100 Hz; this is sufficient for high-fidelity music. High-frequency tones are highly directional, making the location of their source easy.
Precision
Inside the cochlea of a healthy person, about 20,000 fine hairs vibrate when sounds of different frequencies enter the ear. Each hair responds to a particular frequency, giving you the ability to distinguish between 20,000 different musical pitches. In musical terms, you can detect tuning differences of about 5 cents, or 5/100ths of an octave.
Age-Related Hearing Loss
Beginning in the middle-30s, most people begin to lose hearing for the highest frequencies as some of the cochlear nerves deteriorate. Prolonged exposure to loud sounds, disease and other problems accelerate this hearing loss. As a person ages, high-frequency hearing loss progressively increases.