The Circle of Fifths in ChordLab is displayed via menu command cmd-shift-c or by using the Circle of Fifths toolbar button. It then opens into an auxilliary window as seen below. There are several levels of usability in this window that we will explain below. There are two basic control objects in the Circle of Fifths window. A segmented control at the very bottom of the window and the circle itself. To turn the circle place the mouse inside it and drag vertically up and down OR horizontally left and right. To show the current root chord in ChordLab's main window, click the arrow button in the top left corner of the Circle of Fifths window.
In each position the circle of fifths highlights a root note with the yellow rectangle, seven scale tones in white and updates the associated roman numerals in the orange half circle. The letters in white also give us the roots of the 7 base chords and the roman numerals in the inner circle give us the degree and designation. This entire association is referred to as scale degrees, an important concept since we are associating scales with chords. The inner orange circle has 3 different kind of chord types: upper-case numeral for major, lower-case for minor and lower-case numeral plus 'º' for diminished. If we now string out these chords not sorted in fifths, but in seconds like a scale, we get: Ci, Diiº, EbIII, Fiv, Gv, AbVI, BbVII. Clicking a the highlighted root names will sound the associated chord. Try playing these chords in scalar order.
So why is this scale degree thing important? Good question. The answer is that 90% of all songs ever written use nothing but the chords in this association and probably less. So for a song in C minor our goto chords are: Cm, Ddim, Ebmaj, Fm, Gm, Abmaj, Bbmaj. If you ever wondered how some guitar or piano players can accompany a soloist although they have never heard the song, this is what they use. A harmonic domain and its associated base chords.
Key signatures are typically in either major or minor modes. These designations are however somewhat inaccurate. In church mode terms major corresponds to the ionian and minor to aeolian modes respectively. These modes are indicated with a label stating major and another one stating minor just above the segmented control above.
We have then set the display to the right to give us the key signature for Eb major and see 3 flats in the center. On the right side the segmented control has been set to minor (aeo) to look up the key signature for Eb minor and we find it to be 6 flats. Here we are also given an enharmonic equivalent which is D# minor with 6 sharps.
Note: ChordLab's Circle of Fifths is not limites to the classic major/minor key signatures. So to find out how many flats or sharps are given in the Lydian mode for example, jsut set the mode control to "lyd" and then rotate the circle to the desired root.
In order to look up the notes of any of the 7 church modes simply select the desired mode and then rotate the circle to the desired root. In the example above to the left we can now read off all the scale for C major very simply by reading the noted adjacent to the roman numerals:
I C - ii D - iii E - IV F - V G - vi A - vii B
Repeating the same for the graphic on the right side where we are looking up the notes for the D Phrygian scale we get:
I D - ii Eb - iii F - IV G - V A - vi Bb - vii C