test_plan.md

1. Analyze Requirements:

   • Goal: Add a "Vocal Formant Envelope" specifically for formants.
   • Purpose: Create plucky or sweeping vocal filter effects on every note by modifying the formant shifting over time (Attack/Decay).
   • Task mentioned in agent_plan.md: [ ] **Vocal Formant Envelope:** Add a dedicated Attack/Decay envelope specifically for formants to create plucky or sweeping vocal filter effects on every note.
   • Need to add properties to control Formant Envelope (e.g. Formant Attack, Formant Decay, Formant Envelope Amount).

2. Check Current Formant Control:

   • FormantShifter.ts handles formant shifting using a chain of Biquad filters.
   • Currently, it sets static shift values, or linear ramps (updateFilterChain), or LFO (lfo, lfoGain).
   • We need an envelope to modulate f1Shift, f2Shift, f3Shift or simply the detune / frequency of the peaking filters over time, triggered on Note On.

3. Where to implement Formant Envelope?

   • The formant filters are standard BiquadFilterNode created in FormantShifter.ts.
   • In SingingVoice.ts, we trigger note on. When a note is triggered, we can schedule an envelope on the Formant Filters' detune or frequency parameters, similar to how an amplitude or filter envelope works.
   • To do this, we need formantEnvAttack, formantEnvDecay, formantEnvAmount properties.
   • Let's add these to Note parameters (if it's per-step) or global sampler params. Wait, the backlog says "Add a dedicated Attack/Decay envelope specifically for formants to create plucky or sweeping vocal filter effects on every note."
   • We should add global controls for Formant Envelope to SamplerBankParams or similar, and map them in SamplerPanel.tsx UI. We might also want per-step overrides.

4. Investigate Data Structures (types.ts):