Double Bass Lulu's Back in Town Monk Changes

[sebs_washed]

I've been listening a bit closer to Monk's version of Lulu and he and Gales suggest a different progression in the A section throughout the piece. The original changes are C7 - F7 - Bb7 - Eb7, while it sounds like they're playing something along the lines of Db - Cb - Fb - Eb (I think that's what they're getting at in terms of the key). I'm still learning about substitutions, so I'm unclear on if that's what these are or if they're doing something else entirely. Why does this work?

 

[DoubleMIDI]

The first is a bit more difficult (I explain it in a second), but the second and third chord is a simple tritone substitution.

The first original one is a dominant chord. That could be played with halftone-wholetone scale on C7, but they are the same notes of the wholetone-halftone scale on Db (diminished), which is what he played.
Chord progression is Db dim. - B7 - E7b9 - Eb7, I just renamed the root notes enharmonically, as commonly notated in jazz.

Your naming of the root notes is probably more exact than mine in the classical sense of a harmonic progression and keeping all seven (altered) root notes in each scale.

 

[sebs_washed]

The first is a bit more difficult (I explain it in a second), but the second and third chord is a simple tritone substitution.

The first original one is a dominant chord. That could be played with halftone-wholetone scale on C7, but they are the same notes of the wholetone-halftone scale on Db (diminished), which is what he played.
Chord progression is Db dim. - B7 - E7b9 - Eb7, I just renamed the root notes enharmonically, as commonly notated in jazz.

Your naming of the root notes is probably more exact than mine in the classical sense of a harmonic progression and keeping all seven (altered) root notes in each scale.

Thanks for the explanation, that makes a lot of sense now. Is there a specific name for that kind of substitution, or is it just an alteration?

 

[DoubleMIDI]

Is there a specific name for that kind of substitution, or is it just an alteration?

I have no idea if a special name exists for that kind of substitution. I'm not the best in naming conventions, more about what could be done.
But the first chord is not an alteration (which I don't like as a descriptive term, but it isn't the case here anyway), because the scale is the same, it is just a different selection of notes used. I think reharmonization (inside the original scale) would be a better description than alteration for the first chord.