Example 4. Tempo and dynamic curves in Heifetz 1952 (top panel) and Milstein 1956 (bottom panel) recordings of Bach Sonata in A minor, BWV 1003, Andante, mm. 1–12

The black line shows tempo fluctuation, the green (more volatile) line indicates changes in dynamics
(Vertical [y] axis = volume in dB; Horizontal [x] axis = time [measures and beats])

Audio Example 2a. Heifetz

Audio Example 2b. Milstein