I have a relative pitch and I'm a beginner of jazz improvisation. I have a problem in improvisation.
I used to follow the key when chord progression of key changed. (like 'all the things you are' and other modulation chord progression)
so in your case, how do you recognize notes when key changed or in modulation?
and what should I do to fix this problem?
I personally use your second option of thinking of the modulated section in the new key. Modulations happen very frequently in jazz standards and it is much easier to think in the modulated key than to think of the notes and chords as part of the original key. Using the first melody note as an example, thinking of Fa in Ab is much more logical than Te in Eb when you are already in Ab at that point (the ii chord, Bbm7).
Your example of “All the Things You Are” is in Ab, C, Eb, G and E. It’s much easier to just change the key temporarily than think in the original key. Classical music also has many modulations and they are approached and analyzed as such.
In measure we 16 are in Eb. The whole note is Do. As we modulate to Ab I interchange Do to Sol: So la ti re mi fa fa fa (your 2nd version makes more sense to me: Db after the double barline becomes Fa.
But the greater challenge is the next line when the tune modulates to Gm:
I sing sol la do re mi fe (still in Ab) and here I
reinterpret fe = mi (dominante of Gm) mi mi mi re sol mi re do (Bb = do in Gm becomes sol of Eb).
The whole of Misty is in key Eb. That's clear from the key signature - it stays at 3♭ all through. What does happen is modulation - as occurs in so many songs, including many classic ones - and indeed, classical music.
By thinking it 'changes' key, you're not going to improvise, or jazz your way through this, or many other standards. It's probably better to consider two or three bars at a time, where you'll inevitably discover ii-V-I going on. With that information, you can play through the changes, making the whole thing sound more cohesive. True, you'll be changing the set of notes (scales, if you like) more often that if yyou just 'changed key', but it's not going to work just 'changing key' for a middle eight, when several of those changes are only vaguely related to that 'change of key' - too many avoid notes are avaiable!
