A Different Kind of Modal Use

Sometimes, improvising over a backing track that changes keys can be difficult if not prepared correctly. Let's explore different option we have when facing that situation. Let's start by talking a look at the chords of the backing track: B7 and A7.
Those are dominant chords over which we can play a Mixolydian mode.

That means that we could in theory use a B Mixolydian shape over the B7 chord, then switch to A Mixolydian when playing over the A7 chord. That would sound great, but will not be the most interesting approach as it will encourage you to play the same kind of licks as you are using the same scale shape over both keys.

The approach we'll take is slightly different. Let's start by trying to find a common note to both of the B and A Mixolydian. Let's see if the B note can be found in A Mixolydian:

B Mixolydian
B-C#-D#-E-F#-G#-A

A Mixolydian
A-B-C#-D_E-F#-G

As you can see, A Mixolydian does include a B note. Now the question we need to ask ourselves is what scale starting with B shares the same notes as A Mixolydian? The answer is B Aeolian.
We now brought both keys to a common starting note which will help your improvisation sound more melodic as the notes you will play will be all close together.

Make sure you are comfortable with the scales below and experiment!

Have fun!