73.5Level 2 — two common tones

Cmaj7:

C-E-G-B.

Am7:

A-C-E-G.

Common tones:

C-E-G.

That transition can be nearly frictionless.

Now compare:

Cmaj7→D♭maj7.

Almost everything shifts.

Much stronger contrast.

The number of common tones strongly affects perceived smoothness.