The Fifth Interval
In music theory, an interval is the difference between two pitches. Therefore this may be described as horizontal, linear, or melodic if it refers to successively sounding tones, such as two adjacent pitches in a melody, and vertical or harmonic if it pertains to simultaneously sounding tones, such as in a chord. Although learning how to find the fifth may seem complex to begin with, and although it relies on your knowledge of scales, as you practice it becomes much easier. Learning this helps with your sight reading and memorization of music. Additionally as with most things in music the best way to get better at identifying intervals is to practice.
The “Fifth Interval” is the “Fifth” note of the Major scale. The fifth is 7 half steps above the key note of the scale. In lettered notation in C-major the fifth is G, in numbered notation in the key of 1 the plus 7 interval is 8.
The fifth interval is 1.5 greater then the key note. So if the frequency of the keynote is 100 Hertz then the fifth would be 150 Hertz. This specific relationship is easy for the human ear to hear and is fundamental to music composition because it has the feeling of “needing to resolve” back to the key note. Thus many songs have this interval arrangement of going from the fifth back to the key note at the end of songs.
This is an advanced music theory lesson for another lesson check out the Circle of Fifths here.