The ratio of the frequencies of two notes is called the musical interval between them. Certain recognized intervals have been given special names. Thus, a ratio of 9: 8 is called a major tone, 10: 9 a minor tone and 16: 15 a semi tone. Those who have studied music will be familiar with other intervals. For example,the interval between the top and bottom notes of the scale, 2: 1, is called an octave. The interval between c’ and g’, 3: 2, is a fifth and so on.