How it is used · Tritone substitution · Music theory
The substitute resolves down a half step: D♭7 goes to C. Instead of leaping a fifth, the bass falls by step, so II – subV – I has a very characteristic…
How it is used
The substitute resolves down a half step: D♭7 goes to C. Instead of leaping a fifth, the bass falls by step, so II – subV – I has a very characteristic chromatic line: D, D♭, C. It keeps the tension of the dominant and sounds softer and more sophisticated.
Any secondary dominant can be replaced, not just V⁷. And it can be preceded by its own related II: A♭m7 – D♭7 – C. Take care with the melody: the note that sat over G7 must also work over D♭7. A G in the melody, for example, is the ♯11 of D♭7: it works, but with color.