Octave and Rill

Rill went first, because a chord has to start moving before it can go anywhere. "Play your rock." He struck the block chord — solid, all at once, thud. "Now don't hit them together. Roll them — bottom, middle, top, one after another." He did, and the chord rippled out, sparkling. "There's your first spread. That's an arpeggio — the same notes un-stacked across time, so instead of a wall it's a stream." She rolled it again, quick and light. "Hear how it moved? It's not a rock — it's walking. But it's walking on level ground. It ripples along, but it doesn't rise. For the rising —" she looked at Octave — "you need floors."

Octave took over, because rising means having somewhere higher to go. "A chord doesn't have to stay on one floor," he rumbled. He played the boy's three notes low, in the basement, then the same three notes an octave higher, up in the attic. "Same chord — I just moved it up an octave, a whole floor, and it stays the same notes because the octave is just a doubling. That's the second spread: not time, register." He played basement, then attic, and the room felt like an elevator going up. "But notice — that's rising in thuds, one block per floor. It goes up, but it doesn't flow."

Then they combined, and the rock became a rising river of light. Rill began rolling the chord — bottom, middle, top — and instead of stopping at the top, Octave nudged the next note into the next octave, so Rill kept walking, note by note, right up the staircase of registers: bottom, middle, top — the same notes a floor higher — bottom, middle, top — a floor higher still — climbing and rippling all at once, until the chord that had been a rock was a shimmering line sparkling to the ceiling. "THAT," said Rill, "is a chord that climbs." "Two spreads at once," rumbled Octave. "Rill spreads it across time so it flows. I spread it across registers so it rises. Alone —" "— I flow, but only on one floor," said Rill. "— and I rise, but only one thud per floor," said Octave. "Together — arpeggiated and climbing octave after octave — we turn a heavy block chord into a river running uphill. Same notes the whole way, spread across time and register."