Hi,
We will be learning more about tritone substitute in this lesson.
In key of C, ii V I is Dm7 G7 Cmaj7
Tritone substitute also known as flat 5 substitute, will replace the dominant chord,
in this case, the G7 and replace it with Db7.
The new progression will be Dm7 Db7 Cmaj7.
The notes in a Db7 are Db, F, Ab and B
It is actually a G7 alter chord - G7(b9)#11 (with G as the root)
This is the reason why we could use a Db7 instead of G7.
Hope its clear.
Cheers
