Sing the major arpeggio on a hum.
Why this matters: the 1-3-5 arpeggio outlines the tonic chord. If you can sing it cleanly without an instrument, you’ve internalized the home triad — the anchor every melody returns to.
10 trials. Each: hear the arpeggio (1-3-5-3-1), then sing 1, 3, and 5 in order on a hum. Each note within ±50¢ for 2.0s. Hit 8 of 10 to pass.