Hey Friend,
The Perfect Fifth is an interesting interval because it is very similar to the tonic of the key.
When we look at how sound waves interact and resonate, the perfect fifth is the next closest wavelength to the tonic as that of the octave.
Le’s say the frequency value of your open E string note is 165 Hz (the low E sixth string). That means your guitar string vibrates 165 times every second to produce the sound of E.
An octave is double that value, so when you play an E note 12 frets up the neck, the string vibrates at roughly 330 times every second to produce that sound. You’ve effectively cut the string in half by placing your finger on the twelfth fret.
If you split the string into thirds and cut off the lowest third by placing your finger on the seventh fret, you are now playing a perfect fifth interval. This sound wave vibrates at roughly 247 Hz (or vibrations per second).
This frequency resonates well with the tonic note frequency, so they sound really good together. This is one of the reasons power chords are so effective - the two strongest notes from the scale working together produce an extremely solid sound.
Okay, enough physics.
Here is our major scale chart.
Tonic - we call this the root note most of the time; it’s the first note of the scale. In the key of C major, this note would be C.
Major Second - this is one whole step (tone) above the tonic. In the key of C major, this note would be D.
Major Third - two hole steps above the tonic. In the key of C major, this note would be E.
Perfect Fourth - five half-steps above the tonic. In the key of C major, this note would be F.
Perfect Fifth - seven half-steps above the tonic. In the key of C major, this note would be G.
Major Sixth - nine half-steps above the tonic. In the key of C major, this note would be A.
Major Seventh - eleven half-steps above the tonic. In the key of C major, this note would be B.
Perfect Octave - six whole steps above the tonic. In the key of C major, this note would be C.
In the key of C major, that is the shift from C to G. When we look at the scale pattern, we see it’s three whole steps (tones) and a half step (semitone).
1 2 3 4 5 6 7 (8)
C D E F G A B (C)
| | | | | | |
W W H W W W H
Practice the exercises here to get you ears used to the perfect fifth interval.
I found a cool resource to help you memorize what these various intervals should sound like. Earmaster.com has a listing of songs for each chromatic interval with links to Youtube videos for each. Very handy to help train your ears to recognize every interval.
You’d be surprised at how ear training will help your guitar playing. I wish there had been more focus on it when I was growing up! Check it out.
Peace~
Dave
| 
