What metric modulation means here
Metric modulation is the feeling of a new pulse relationship appearing without changing the underlying barline. In these studies, the A section stays grounded, then the B section implies a new pulse: 3 over 4, half-note triplets, dotted quarter notes, 2 over 3, or a mixed-meter modulation inside a standard form.
The drums are muted by default so the piano and bass make the pulse shift easier to hear. Each page loops the full study four times by default, so you can stay inside the transition long enough for it to settle.