The essence of sound
(INTRODUCTION TO SYNTHESIZERS
by Thomas Kolb)

In order to fully understand how synthesizers work, we must first understand the physics behind the phenomena we perceive as "sound". So, what is a sound?

The air surrounding us consists of gas-particles. If you force a number of these particles to move, they will create a wave traveling from one particle through the next, in all directions away from the source. It's just like when you throw a stone into a pond - the water particles will create ripples or waves, moving away from the center.

Sound-waves are also initiated from a source, like a car engine, a slamming door or a finger plucking a guitar string. These ripples, or vibrations travel through the air and reach our ears, where they will set our eardrums into motion. This motion is in turn perceived by our brains and interpreted as a "sound".