From Sound to Tone

The cat meows, the phone rings, the plastic bag rustles, the popcorn crackles, and the car honks. We're all familiar with these sounds. But how does the act of "making noise" happen, and how can we perceive it? It's not as simple as we might imagine because tones don't emerge out of nowhere and then travel into our ears.

Instead, it has more to do with the concept of sound. Sound is the vibration of matter like air. When air is set in motion, we can perceive sounds. Where there is no matter, such as in a vacuum, we can't hear anything.

For example, if a water bottle falls on the desk, the air is displaced at that spot. It becomes compressed and quickly spreads out in all directions. You can feel this air pressure, for instance, when a large bus passes by, or you stand close to the speakers at a concert.

Sound moves through the air in waves, known as sound waves. These waves can also be measured. For example, if the sound waves follow a pure sine curve, it's referred to as a tone. However, pure tones are rare in nature. Most auditory events are composed and not sinusoidal vibrations.

A note is a composition of different tones, while noise consists of infinitely many individual vibrations.

But that's not all. We can not only hear things but also perceive how loud they are or in what pitch they occur. We derive loudness from sound pressure because sound waves are nothing more than pressure waves. The higher the pressure, the louder we perceive the noise.

Through the number of vibrations, we perceive pitch. If more vibrations occur in the same time as with another tone, we perceive the auditory event as higher. That is, more vibrations mean a higher auditory event.

The human ear is sensitive to pressure changes and can precisely recognize sound pressure and the number of vibrations. How the ear accomplishes this will be explained in the next article, "The Ear."

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