Tonal Center Modulation

Tonal center may be simply defined as the scale that the letters and tones of the harmony come from or belong to. Any scale may be the tonal center. For this lesson, we’ll use the major scale.

Any given harmony (arpeggio or chord) may belong to several different scales or keys. For example, a C major chord may be the I chord in the key of C major, the IV in G major or the V in F major. The key in which a particular harmony is in at any given moment is known as the tonal center.

The following illustrates a harmony progression in the tonal center of C major (scale or key). Even though the harmony changes, the C major scale tonal center does not. In other words, the C major scale is played with all the changing harmonies.



Transpose means to play the same song in a different key or tonal center. Modulation means a change from one tonal center key to another within a song. Generally speaking, modulation is used to “break-up” the tonal monotony that is created when harmonies of only one tonal center are used. See page 81 of Bass EncycloMedia for more about Tonal Center Modulation.

Modulation expands the tonal harmony of a song and there can be many key changes (modulations) before the song ends. To identify the key of these tonal center modulations you must be able to recognize the dominant seven harmony(V⁷, "five-seven") of each newly modulated key.

The reason why the dominant seven harmony is so useful in determining the tonal center (scale and key) is because there is only one V⁷ harmony in the major scale. Therefore, the ⁷ harmony immediately reveals the tonal center key with absolute certainty. For example, if the harmony is A⁷ the tonal center is D major, if the harmony is D⁷ the tonal center is G major, and if the harmony is G⁷ the tonal center is C major. It is essential to identify key change modulations in order to know which tonal center scale to play as the harmony changes.



Next time we’ll introduce modes and discover how they may be used to solo with an even greater sense of harmonic motion.
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