A few of these are shown in the figure. Some of these may be familiar to you. Many of these terms refer to the magnitude of the sound wave. These commonly describe the magnitude of pressure variations on a logarithmic scale, the decibel or dB. We often also describe how rapidly the pressure magnitude varies or how many times it rises and falls in a unit of time this is called frequency and is commonly referred to as pitch. When the pressure varies rapidly, high frequencies or high-pitched sounds are produced like a shrill whistle.
Slower variations produce low frequency sounds such as a foghorn.
The magnitude of the pressure variation can be so small that it can not be heard to so loud that it causes pain. The chart at the right provides an indication for this range on the decibel scale. A sound pressure level of 0 decibels is barely audible, while a sound level of 140 decibels is painful and can lead to hearing loss with prolonged exposure. Many sounds are unpleasant or unwanted - these are called noise. However, the level of annoyance depends not only on the quality of the sound, but also our attitude towards it.