Since there is no link to a video, I'm just going to talk some theory on the circle of fifths, which is usually what guitar dudes are talking about when they say "cycle of fourths." Circle of fifths and circle of fourths fundamentally the same material, just one moves through the keys one way the other goes the other way around.
While the circles of fifths and fourths aren't advanced music theory lessons, it is necessary to know, the fundamentals of pitch in music first. You need to understand what a half step and a whole step are, and note names and where those notes are on your fingerboard (fretboard).
Every fret on the neck of a bass guitar is a half step, therefore every two frets are a whole step.
Having said that, one must also know that the major scale is produced by playing a fixed set of steps. A Whole step, followed by a whole step, then a half step, whole step, whole step, whole step, half step. In the key of C Major, this would be C-D-E-F-G-A-B-C. Whole, whole, half, whole, whole, whole, half.
The circle of fifths (or fourths if you'd rather go the other way), is more of a learning tool for learning your key signatures and how they relate to one another more than anything else.
Starting at C Major (the natural key signature with no flats or sharps) and going through by fifths, every subsequent key will add a sharp.
C Major - Natural
G Major - One sharp
D Major - Two sharps
A Major - Three sharps
E Major - Four sharps
B Major/Cb Major - Five sharps/Seven flats
F# Major/Gb Major - Six sharps/Six flats
C# Major/Db Major - Seven sharps/Five flats
Ab Major - Four flats
Eb Major - Three flats
Bb Major - Two flats
F Major - One flat
C Major - Natural
Most theory books actually have a circle diagram that looks like a clock face with twelve places on it for the twelve keys. This really helps visualize the abstract concept I'm trying to explain in a web forum.
The placement of the # in the key signature is on the scale degree directly below (the seventh scale degree). In G Major, place the sharp on the F: G-A-B-C-D-E-F#-G. Moving forward, keep the previous sharp and place the next sharp on the scale degree directly below again: D-E-F#-G-A-B-C#-D.
If starting on C and going through the circle of fourths (the opposite way of the circle of fifths, or starting at the bottom of the chart I made and working up) flats are added on the fourth scale degree. F-G-A-Bb-C-D-E-F. Bb-C-D-Eb-F-G-A-Bb. And if you know your fingerboard, you'll see that this holds to the whole, whole, half, whole, whole, whole, half pattern that started the lesson.
The circle of fourths would be going through the circle of fifths backwards, but the relationships remain the same.
Because there are only so many notes to augment or diminish, you can only have up to seven flats or sharps in a key signature. Sometimes you hear people talking about playing in A#, but that Major key would have ten sharps and no practical application, therefore, it's actually Bb.
Now, you can do the same thing with minor keys, because the sixth scale degree of the Major scale is the starting point of the relative minor scale. The steps of a minor scale are whole, half, whole, whole, half, whole, whole. Which, if you noticed, is the major scale steps out of cycle, starting on the sixth scale degree.
Once again starting in C Major:
C-D-E-F-G-A-B-C, A is the sixth scale degree, and is therefore the starting point of the relative minor scale of C. A-B-C-D-E-F-G-A, is the A minor scale, which contains no sharps or flats, just like C Major. A minor is the relative minor scale to C Major, and C Major is the relative Major scale to A minor. And, once again, holds true for every key we've discussed.
When I say "minor" scale, I'm only talking about the natural minor scale, because you'll learn about other minor scales later on in your studies.
I hope this helps, because it's a lot to take in if you're starting from scratch. Don't give up and keep at it.
Last edited by White Beard : 10-29-2013 at 03:09 AM.