Every chord, broken down to its root, 3rd, and 5th (or 7th). Learn the 3 inversions and see exactly which marimba bars light up for each one.
Shown on a marimba layout — the tonal reference view for a drum kit's mallet percussion.
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The method: a triad has 3 tones (root, 3rd, 5th). Playing it starting from a different chord tone gives you 3 inversions — Root Position, 1st Inversion, 2nd Inversion — depending on which tone is lowest. It's the same triad every time, just reordered low to high.