Watch the Dim 7 as 7b9 No Root online guitar lesson by Brad Carlton from Guitar Lab: Diminished Moves Vol. 1
Many times a dim 7 chord is a (dom) 7b9 chord in disguise. One must consider the bassline because the added fifth note completes the total harmonic picture. The formula for a 7b9 chord is: 1, 3, 5, b7, b9. If we apply this formula to a C root, it would yield the notes C, E, G, Bb, Db. If you analyze the notes E, G, Bb, Db in the key of E, the resulting scale degrees would be 1, b3, b5, bb7 which are the notes in a dim7 chord. This results in a formula which allows you to view a 7b9 chord as a slash chord. View the 7b9 chord as a iii dim7, v dim7, bvii dim7, or bix dim7 over the root. For example: G7b9 = Bdim7, Ddim7, F dim7, or Ab dim7 over a G bass note. This concept will be used in the following lessons which examine this 7b9 chord resolving to either a minor or major harmony.