Tones & music

Whether it's your favourite song in your headphones, a ringtone, or the hum of the fridge: everything you hear is vibrations in the air. Once you understand what makes a tone high, low, loud, or quiet, you'll hear music with completely different ears.

Pitch is frequency

How high a tone sounds depends on how fast the air vibrates. The number of vibrations per second is called frequency and is measured in hertz (Hz). Concert pitch A, which orchestras use to tune their instruments, is fixed at 440 Hz: the air vibrates 440 times per second. The higher the frequency, the higher the tone. Double the frequency and you jump exactly one octave up: 880 Hz is an A again, just higher. Halve it and you go one octave down: 220 Hz is the A below.

Loudness is amplitude

How loud a tone is depends on the amplitude: it tells you how strongly the air swings back and forth. Large amplitude means loud, small amplitude means quiet. In everyday life, loudness is measured in decibels (dB): whispering is around 30 dB, a normal conversation 60 dB, a rock concert over 100 dB. From about 85 dB, constant noise can damage your hearing, so it pays not to turn your headphones all the way up.

Why does a guitar sound different from a flute?

If a guitar and a flute play the same note, you still hear the difference immediately. The reason is overtones: an instrument hardly ever vibrates at just one single frequency, but at many quieter, higher frequencies at the same time. This mix is different for every instrument and gives it its timbre. By the way, your ear doesn't hear everything: young people perceive roughly 20 Hz to 20,000 Hz, and the upper limit drops with age. Dogs and bats hear far beyond that.