Db Dominant 7

Db Dominant 7, written Db7, is built from Db, F, Ab and Cb: the root, major 3rd, 5th and minor 7th.

Its 3rd and 7th, F and Cb, are its guide tones: they say what kind of chord it is, so voicings are built around them and the root is often left to the bass. G7, a tritone away, has the same two notes the other way up, so it can stand in for Db7 as its tritone substitute.

In the progressions here, Db7 is the V7 of the Major ii-V Progression in Gb, the ♭VII7 of the Backdoor ii-V-I Progression in Eb, the ♭II7 of the Tritone Sub ii-V-I Progression in C, the ♭III7 of the Tritone Sub Turnaround in Bb, the I7 of the Whole-Step ii-V Chain in Db and the ♭VI7 of the Half-Step ii-V Chain in F.