I need help analysing weird chord progression

Question

Here is the progression, bar-by-bar (newline after each 4 bar phrase):

Verse:

D | Bm7 | Gmaj7 | Em9

D | Bm7 | Gmaj7 | Fmaj7

Chorus:

Abmaj7 | Abmaj7 | Abm7 | Abm6

Ebmaj7/G | Ebmaj7 | F7 | F7

Fm7 | Fm7 | Fm7b5 | Bo7 Bb7

The chorus is specifically what I'm looking at. My best guess, as somebody still learning harmonic analysis, is the key center is Eb? Looking at the Bb7 at the end of the chorus. I honestly am pretty lost-- I know there's lots of odd modal interchange and stuff.

Answer 1

Yes, the chorus is in Eb, and it starts on the IV chord:

Chorus

IV7 | IV7 | iv7 | iv***

I6/5 | I7 | V/V | V/V

ii7 | ii7 | iiø7 | viio4/3 ** V7

**Here the Bo7 is operating as an approach from above to the Bb7, as well as arguably adding a tinge of diminished to the Bb7 sound itself (could be construed as a Bb7b9, which actually has all the notes of a Bo7 chord built-in). The reason it is notated as a chord built on degree vii (instead of #V, as B is the #5th note of Eb) is because the notes in Bo7 are also in Do7: B D F Ab -> D F Ab B. Do7 is the fully-diminished leading tone chord in Eb, so I just took it from there and indicated it was in inversion (the 4/3), which gives the correct "layout" of the chord to make Bo7.

*** The Abm6 could be construed as an inversion of F-7b5 (iiø7) for analysis purposes but I'm leaving it as a minor iv chord for simplicity/practicality.

And for the verse (D major):

I | vi7 | IV | ii9

I | vi7 | IV7 | bIII7

The Fmaj7 (bIII7) chord is indeed a modal mixture chord (arguably borrowed from D minor).