Sound is created when something vibrates through a medium. In this case, this medium is air and the vibration comes from the computer's speakers. Your eardrums pick up the vibration and signal your brain, which interprets it as sound. This vibration through the air creates pressure fluctuations. Faster fluctuations create a higher sound wave frequency, leading you to hear a higher pitch. The amount of pressure in each fluctuation is known as its amplitude. Higher amplitude causes you to hear louder sound. In short, sound waves are just changing amplitudes over time, as shown in Screenshot.
Screenshot Sound waves are composed of changing amplitudes over time.
Digital sound, such as that in CD audio and many computer sound formats, contains sound as a series of discrete samples of the sound's amplitudes. The amount of samples stored per second is called the sample rate. CD audio, for example, has a sample rate of 44,100Hz. Of course, higher sample rates result in a more accurate audio representation, and lower sample rates mean poorer quality but a smaller file size. The samples themselves are typically 16 bits, giving 65,536 amplitude possibilities. Many sound formats allow for multichannel sound. CD audio has two channels, one for a left speaker and one for a right speaker.