What is frequency? Definition and examples
In relation to sound, frequency is a measure of how many sound waves pass a point during a particular span of time (usually one second).
Frequency is expressed in hertz (Hz), a unit of measurement named for Heinrich Hertz, a German physicist who proved the existence of electromagnetic waves – which had previously only been theorized. One hertz is “equal to one cycle per second”.
Though closely related to pitch, where frequency is a physical measurement, pitch is a subjective perception of a sound’s high- or lowness. However, the pitch of a sound is determined by the frequency of the soundwaves producing it. As a result, “a higher frequency produces a higher pitch, and a lower frequency produces a lower pitch”. The quicker the vibrations, the higher the pitch; the slower the vibrations, the lower the pitch.
The frequency range audible to humans is between 20 and 20,000 Hz (though “[this] range tends to contract” with age).
Different frequencies of sound have different physiological effects on the body. Low-frequency sounds like a bass note “activate the parasympathetic nervous system”, leading to a state of calm and an accompanying decrease of heart rate and blood pressure and the untensing of muscles. On the other hand, high-frequency sounds – for example, a sharp whistle – activate the sympathetic nervous symptom, activating the fight-or-flight response to possible danger, increases heart rate and causes “stress hormones like cortisol [to be] released into the bloodstream”. This physiological response prepares our body for potential danger or heightened awareness.
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