Weeks 11-12 · harmony · continuous-frame pitch tracking
Lock onto the guide. Track every frame, not just every note.
The rule
pass: median ≤ 30¢ on 80% of voiced frames
Grey step line is the guide’s pitch over time; emerald is the sung trace; the pale band is ±30¢. Frames inside the band count toward the 80% threshold. The classic failure is note-onset lag — every step drift starts at the moment the guide jumps and your voice is still on the previous pitch.
Hear it first
Listen to the guide melody alone — it’s a Twinkle-Twinkle pattern at 80 BPM, 4 bars. Then hear it doubled by a sung trace that tracks tightly, vs. one that drifts flat at each step. Your goal is the first.
What’s happening.Unison is the cleanest harmony — two voices on identical pitch. But measured frame-by-frame (50 ms windows), even “unison” performances spread 30-80¢ on the average singer. 30¢ is choir-quality alignment, looking at the median so a wobble or two doesn’t blow the trial. The 80% threshold accepts some onset settling without giving away mid-note drift.
Why a 4-bar melody, not isolated notes. Single-note matching tests one closed loop. A moving line tests repeated closing of that loop — every time the guide changes pitch, you have to re-acquire. Twinkle-Twinkle uses small steps and a few leaps, so the test covers both step-tracking and jump-targeting in one phrase.
Why this is the bridge.Choir entries, doubling another singer, recording a guide track — all of it depends on this exact skill. It’s also the warm-up for the harder harmony lessons in this phase: harmony-over-drone (sing a different pitch over a held one) and a-cappella-resolve-tonic (no guide at all). If unison tracking isn’t solid, those are guesswork.
Session ahead
5 trials · 4-bar guide at 80 BPM · sing along on any vowel · median ≤ 30¢ on 80% of voiced frames · 4/5 promotes.