Sound begins with a vibration of an object. Transmitted to ours ears through a medium (usually air.)
relative highness or lowness that we hear in a sound. The pitch of a sound is determined by the frequency of its vibrations. The faster the vibrations, the higher the pitch; the slower the vibrations the lower the pitch. The smaller the vibrating object, the faster its vibrations and the higher its pitch. 
The distance in pitch between any two tones. Two tones will sound different when they have different pitches. 
When tones are separated by the interval called an octave, they sound very much alike. The interval of an octave is important because it is the interval between the first and the last tones of the familiar scale.