Rolls and Tremolo

Use a-m-i (ring-middle-index) to pluck the same set of high strings rapidly in turn, like droplets rolling down one after another, producing an unbroken stream of notes. The key is even spacing between the three fingers and consistent force, usually paired with the thumb walking a beat on the bass.

On a single string, use a-m-i (or p plus a-m-i) to pluck repeatedly, extremely fast and extremely even, creating the effect of “one long note shimmering continuously,” as in the latter section of “Romance de Amor” or “Recuerdos de la Alhambra.”

First play the three notes a-m-i clearly, slowly and evenly spaced (with the metronome, one triplet per beat), then speed up bit by bit. Always put “even” ahead of “fast.”

The trouble is almost always the ring finger a — it's the weakest and the most likely to throw off the rhythm; the key is the independence of m and a. First practice p-a-m-i slowly on a single string, slow enough that all four notes are perfectly even in rhythm and perfectly equal in volume — that's the foundation.

Then do “accent rotation”: at slow-to-medium tempo, take turns accenting different fingers, focusing on accenting m (highly recommended); only drill a briefly at slow / medium tempo, don't force it at high speed. You can also alternate p-m-p-m to specifically work on m-a independence.