La Campanella
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Third densest in the library, and famous for something else entirely
La Campanella is 4,064 notes over 4:21, peaking at 28.0 notes per second. Only Un Sospiro at 31.4 and Hungarian Rhapsody No. 2 at 29.6 are denser, and all three are Liszt.
So the reputation is earned. But it is earned for the wrong reason, and this is the clearest place in the library to say so plainly: what makes La Campanella famous is the jumps, and note density cannot see a jump.
The piece is named for a bell, and the bell is a single repeated high note that the right hand has to hit accurately while leaping more than an octave to reach it, again and again, at speed. Our measure counts how many notes arrive per second. It does not count how far your hand travelled to get to each one. On this piece, the distance is the difficulty.
What the chart does show
Look at the piano roll and the leaps are visible even though the number cannot express them: the cyan right-hand notes sit in two separated bands, a melody in the middle and a thin line of repeated notes far above it, with nothing between. That gap is the hand travelling. A piece of comparable density with the notes packed into one band, like Flight of the Bumblebee, is a genuinely different physical problem.
This is why we publish the measure with its limits attached. It is one axis, honestly labelled, and La Campanella is the piece that proves one axis is not enough.
Playing it here
Take the right hand alone first, in Practice mode, while Klaviero plays the left. The leaps are the whole job and there is no point rehearsing them against a moving target. Rhythm mode judges every note PERFECT to MISS, and a missed bell note breaks the combo like any other.