Look at the diagram above. The compressions, in which particles are crowded together, appear as upward curves in the line. The rarefactions, in which particles are spread apar
…t, appear as downward curves in the line. Three characteristics are used to describe a sound wave. These are wavelength, frequency, and amplitude. Wavelength; this is the distance from the crest of one wave to the crest of the next. Frequency; this is the number of waves that pass a point in each second. Amplitude; this is the measure of the amount of energy in a sound wave. Pitch This is how high or low a sound seems. A bird makes a high pitch. A lion makes a low pitch. Sounds also are different in how loud and how soft they are. The more energy the sound wave has the louder the sound seems. The intensity of a sound is the amount of energy it has. You hear intensity as loudness. Remember the amplitude, or height of a sound wave is a measure of the amount of energy in the wave. so the greater the intensity of a sound, the greater the amplitude. Pitch and loudness are two ways that sounds are different. Another way is in quality. Some sounds are pleasant and some are a noise. Compare the two waves on the right. A pleasant sound has a regular wave pattern. The pattern is repeated over and over. But the waves of noise are irregular. They do not have a repeated pattern. By the content and style of writing I'd say that was for very early introductions to physics, in schools. It rather over-simplifies things and could be misleading. Intensity is the flow of energy at a point, while power is the rate of energy conversion. You can have considerable power at low intensity or vice-versa: many species of bat can emit ultrasonic hunting echo-location calls at well over 100dB sound pressure-levels, but their power is extremely low. Whilst not disputing the comment, noise is not a measure of aesthetics. It is a random, incoherent jumble of signals of many different frequencies and their harmonics, within a fairly wide band-width. The hiss of gas from an opened bottle of fizz, and the babble of a stream or the ever-chnaging swoosh of small waves breaking on a beach, are all examples of noise that many people would think pleasant! (MORE) 
