The dominant seventh is the engine of tonal music — the note that makes a V chord pull home. You can’t filter it out: it appears in 1,272 of MAESTRO’s 1,276 pieces, so removing the pieces that contain it would delete the corpus. So you edit it out, note by note, and keep every piece.
The edit you can hear
A close relative of this experiment is the modalization: flatten the leading tone everywhere, and major collapses into Mixolydian. Here is Bach, then Bach with every leading tone flattened — the same kind of transform the models were raised on. Listen to the cadences go slack.
Bach, then Bach with the leading tone flattened
In the edited version the pull toward the tonic goes slack and the piece drifts modal. Over the corpus this transform moved 499,965 notes — 7.1% of MAESTRO.
The two models, composing: control vs a model that never saw a leading tone. The modal model leans on the flat seventh and reaches for minor — yet still plays the leading tone about two-thirds as often as control. It was never shown one.
The two models, composing from the same seed
Same architecture, same steps, same seed phrase — the only difference is whether the leading tone was in the training data.
Subtonic / leading-tone mass in generations: control 0.049 / 0.052 (ratio 1.06); modal seeds 0.042 / 0.060 (1.43) and 0.033 / 0.072 (2.17). 400 clips per model, scored by the same detector.
The probe on the seventh itself
Edit the seventh out of every dominant chord, train, and probe. The dominant-seventh model still expects the seventh at roughly 90% of the control’s rate — reconstructed from the root, the third, and the resolution that surround it, none of which the edit touched.
The verdict
The seventh is a foregone conclusion given the harmony around the hole. A model rebuilds it because the grammar entails it. This is the tonal-music version of the result; the surprise came later, when the same thing happened in metal, which has no functional harmony at all.
Researcher notes
- Sonority ablation. Removing struck sevenths exposes new sonorities, so the transform iterates to a fixed point — a single pass leaves residual dominant sevenths behind.
- Two knobs. Flattening degree 7 everywhere (modalize) versus only inside dominant chords gives two different models; both reconstruct, and both feed the playground.