Hi there. I read your question with interest.
Music needs the sense of movement. To modulate is to “move” either inside the same key or to another key, otherwise music would be very boring. Modulation is how we call this movement; “to modulate” is to move the harmony (chords) and the melody to another key, simple as that.
The cycle of fifths is the main and most important tool to study and apply the art of modulation (among other tings). So, it is of paramount importance to learn “at exhaustion” the movement of the keys and notes in the cycle. Without this knowledge one can easily get lost and misunderstand the written music in a lead sheet, for example.
I downloaded How High the Moon lead sheet in GMj key and tried to understand its harmonic structure. One very important thing when studing a sheet of music, is to “
MAP its harmony”. In occidental music, specially in jazz, the most important movement is from ii to V7 to I (2 5 1 the movement from the supertonic (2nd degree), to the dominant (5th degree) and than to the tonic (1st degree). This is called a perfect cadence, it can be used throughout the music, and generally the music ends like this, with a perfect cadence.
I Maped it as you can see in the figure. The music starts with a pickup in the GMj key. Than it modulates to FMj, to EbMj, to GMj again, and, by means of a “turn around’ (Am7 to D7) returns to its main key center of GMj. By doing this the composer could fit its moving melodic line in a consistent way and with a sense of an agreeable harmonic-melodic sound to the ear.
Mike, this is te secret:
MAP ITfind the sequences of ii V I (2 5 1) to have a general idea of the harmony (doing this it makes easier to internalize the sounds and learn the music by heart (Obs.: learning the lyrics, helps the brain in this process). But than, suddenly appears some imprecise movements, in this music (Am7 to D7 without going to the I, the tonic). This is called a Deceptive Cadence, or half cadence on incomplete cadence. The composer uses it (as passages?) to be in accordance with its melodic line, for example, in the passage Am7 D7 and than to Gm7 (instead of GMj). Why he did this? Observe, he just used another musical concept by means of the use of the relative parallel minor Gm7 (of GMj). This parallel Gm7 has in its signature Bb and Eb. This allowed him to borrow from the harmonic minor Gm7, both Am7b5 and D7b9, giving an extra flavor to the sound to end in GMj, in a perfect cadence. Observe tat te dominant7 D7 is altered by the presence of the b9 (Eb), wich continues nicely with the previous Eb, the flat 5 alredy present in the Am7b5.
The other Am7 D7, is also a defective cadence. It continues with a Bm7 (that is the 3rd diatonic degree of GMj wich than goes to a Bb7 (just a passing note) to land a half step bellow Am7, than goes to D7, in a perfect turn around to GMj tonic key.
That is it Mike. I hope this helps.
A few ideas for you:
MODULATION:
MINOR MODES
CYCLE 5