docs(TODO-1.0): fold in Daniel's answers — radio none-state, knot curve-drag, Filter ranges/label, dual-state Spline EGs

TODO-1.0.md

@@ -9,6 +9,12 @@ post-Q layout at execution time. Each item preserves Daniel's raw ask verbatim
 as the source of truth, then breaks it into behavior, open questions, and an
 observable acceptance gate.
 
+A follow-up answer round from Daniel (2026-07-28) settled most of the open
+questions. Each item now carries his follow-up verbatim alongside the original
+ask; settled answers are folded into **Behavior** (marked *settled by
+follow-up*), and only the genuinely unresolved remainder stays under **Open
+questions**.
+
 Ordering note: item 1's curve/overlay treatment explicitly anticipates item 2's
 filter envelope ("filter to be added"), and item 3 layers on both. They can land
 in sequence or together, but 1 and 2 are prerequisites for 3's full surface.
@@ -34,6 +40,12 @@ in sequence or together, but 1 and 2 are prerequisites for 3's full surface.
 > contrasts poorly against the primary green waveform display. Change those to
 > tertiary purple.
 
+**Daniel's follow-up (verbatim, 2026-07-28).**
+
+> yes, one overlay (or none). Everything besides Hold and Sustain, right? "is
+> 1.0 the linear neutral" CLAUDE, y=x^1.0 is linear!! of course! yes dragging
+> on the segment (add a round knot midsegment) adjusts the curve.
+
 **Intent.** Grow the envelope-overlay editor from an amp-only fixture into the
 shared graphical surface for every envelope in the instrument, and give every
 envelope shapeable (non-linear) segments — while fixing the blue-on-green
@@ -46,11 +58,22 @@ contrast failure.
   gains a radio switch in the corner of its deck. Selecting a deck's radio
   makes *that* envelope the one displayed and editable in the graphic waveform
   overlay — replacing today's behavior where the Amp AHDSR is always the
-  displayed envelope.
+  displayed envelope. The switch is exclusive: **one overlay-active envelope at
+  a time, or none** — no-envelope-shown is a valid state, not an error.
+  *(Settled by follow-up.)*
 - **Segment curve values on all envelopes.** Amp AHDSR, Pitch AD, and Filter
   AHDSR all gain an editable curve value per *sloped* segment. The curve is an
   exponential function; the per-segment parameter is the exponent scalar,
   range **0.1 to 10**.
+- **Which segments are sloped.** **Every stage except Hold and Sustain** — for
+  an AHDSR that is Attack, Decay, and Release; for the Pitch AD, both stages.
+  *(Settled by follow-up.)*
+- **Linear neutral.** Exponent **1.0 is the linear neutral** (y = x^1.0 is
+  linear). *(Settled by follow-up — emphatically.)*
+- **Curve editing in the overlay.** Dragging on a segment in the overlay
+  **adds a round mid-segment knot** whose drag adjusts that segment's curve —
+  the overlay is a curve-edit surface in its own right, alongside (not instead
+  of) the inner dial. *(Settled by follow-up.)*
 - **Inner dial on curvable-segment knobs.** Every knob-deck radial knob that
   controls a sloped, curvable segment gains an **inner dial**: its own inner
   arc, its own hover accent (tertiary purple), its own needle, and its own
@@ -63,30 +86,28 @@ contrast failure.
 
 **Open questions.**
 
-- **Radio exclusivity + default.** "Radio" implies exactly one envelope is
+- **Default overlay selection on open.** Exclusivity and the none-state are
-  overlay-active at a time across all decks — confirm that reading, and
+  settled; what is the default when the editor opens — the Amp AHDSR (today's
-  confirm the Amp AHDSR remains the default selection on open.
+  behavior) or none?
-- **Which segments are "sloped."** Per envelope type, which segments carry a
+- **Pre-existing instances.** Should saved instances from before this change
-  curve dial? (E.g. Attack/Decay/Release obviously slope; Hold and Sustain
+  load with every curve at the linear equivalent (exponent 1.0) so their sound
-  presumably do not — needs Daniel's confirmation per stage.)
+  is unchanged? (The neutral point itself is settled; this is only the
-- **Curve default and neutral point.** Is exponent 1.0 the linear/neutral
+  load-behavior half. The product requirement is "old instances sound
-  default, and should existing saved instances load with all curves at the
+  identical.")
-  linear-equivalent so their sound is unchanged? (Persistence extension is
-  implied; the product requirement is only "old instances sound identical.")
-- **Curve editing in the overlay.** Is the curve exponent editable *from the
-  overlay itself* (e.g. dragging a segment's belly), or is the inner dial the
-  sole curve-edit affordance and the overlay edits node positions only?
-  Daniel's ask specifies the dial; overlay curve-drag is not stated either way.
 
 **Acceptance criteria.**
 
 - Each envelope deck shows a corner radio switch; activating one puts that
   envelope in the overlay, editable there, and the overlay tracks the switch
-  immediately.
+  immediately. At most one envelope is overlay-active; with none active, the
+  overlay draws no envelope.
 - Every curvable-segment knob shows the inner dial (inner arc, tertiary-purple
   hover accent, needle, numeric label); sweeping it through 0.1 → 10 visibly
   reshapes the overlay segment and audibly reshapes the envelope on played
-  notes.
+  notes. Hold and Sustain knobs carry no inner dial.
+- Dragging on an overlay segment adds a round mid-segment knot; dragging the
+  knot adjusts that segment's curve, and the segment's inner dial reflects the
+  same value.
 - Overlay envelope segments render in tertiary purple and are clearly legible
   against the primary green waveform.
 - A project saved before this change reopens with unchanged audible envelope
@@ -105,6 +126,13 @@ contrast failure.
 > mod amt, then the AHDSR controls as described above. The knob deck row will
 > then be relaid out in signal flow order: pitch -> filter -> amp
 
+**Daniel's follow-up (verbatim, 2026-07-28).**
+
+> modes beyond the pass filters will be added later. cutoff range full audio
+> spectrum, log scaled, fully open to fully closed, Q should go from 0.1 to 10
+> again, scaled around root 2 at the center. mod amt targets cutoff, -100% -
+> +100% to cover full range from either end. per-voice. label it "Filter"
+
 **Intent.** Add the instrument's first filter stage — resonant high-pass and
 low-pass — as a new fixed point in the per-voice signal path, with its own
 AHDSR envelope, and make the knob-deck row read in signal-flow order.
@@ -120,28 +148,35 @@ AHDSR envelope, and make the knob-deck row read in signal-flow order.
 - **Parameters.** Mode, cutoff, Q, and mod amt — then the AHDSR controls,
   treated exactly as item 1 specifies (curvable sloped segments with inner
   dials, overlay editability via the filter deck's radio switch).
+  *(Ranges settled by follow-up:)*
+  - **Mode:** high-pass and low-pass now; **modes beyond the pass filters are
+    explicitly deferred to later.**
+  - **Cutoff:** the **full audio spectrum, log scaled**, from fully open to
+    fully closed.
+  - **Q:** **0.1 to 10** (the curve-exponent range again), scaled so **√2 sits
+    at the center** of the control.
+  - **Mod amt:** **bipolar, −100% to +100%**, targeting **cutoff** — covering
+    the full range from either end.
+- **Per-voice.** The filter processes **per voice** — each sounding voice runs
+  its own filter with its own envelope state. *(Settled by follow-up.)*
+- **Label.** The user-facing deck-group label is **"Filter"**. "MM preamp" is
+  working shorthand for the DSP lineage, not UI text. *(Settled by
+  follow-up.)*
 - **Deck reorder.** The knob deck row is relaid out in signal-flow order:
   **pitch → filter → amp**.
 
 **Open questions.**
 
-- **Mode list.** Is mode a discrete selector, and over exactly which entries?
+- **Other mod sources.** Mod amt targeting cutoff is settled; whether any
-  "Resonant high and lowpass" confirms HP and LP; whether band-pass/notch or
+  other mod sources (velocity, key-tracking) are in scope now or deferred is
-  multiple slopes exist depends on the Cortex-M4 source and Daniel's intent.
+  unstated.
-- **Ranges and units.** Cutoff range (Hz), Q range, and mod-amt range/polarity
+- **Parameter storage: per-zone or per-instance.** Per-voice *processing* is
-  (unipolar or bipolar?) are unstated — likely settled by the Cortex-M4 code
+  settled, but it is compatible with either storage side. Existing playback
-  plus a Daniel call at implementation time.
+  parameters live per-zone with Sample/Zone panel parity; VOICE and MASTER are
-- **Mod routing.** "Mod amt" presumably scales the filter AHDSR's modulation of
+  per-instance exceptions. Which side do the filter *parameters* fall on?
-  cutoff — confirm the target is cutoff and whether any other mod sources
-  (velocity, key-tracking) are in scope now or deferred.
-- **Scope: per-zone or per-instance.** Existing playback parameters live
-  per-zone with Sample/Zone panel parity; VOICE and MASTER are per-instance
-  exceptions. Which side does the filter fall on?
 - **Neutral default.** Should the filter default to a bypass/neutral state so
   pre-existing saved instances (and freshly loaded captures) sound unchanged
   until the user engages it?
-- **Display name.** Is "MM Preamp Filter" the user-facing label for the deck
-  group, or working shorthand?
 
 **Acceptance criteria.**
 
@@ -149,11 +184,18 @@ AHDSR envelope, and make the knob-deck row read in signal-flow order.
   pipeline point: the filter acts on pitched (post-pitch-envelope) signal, and
   the amp envelope still shapes the filtered result (audible ordering:
   pitch → filter → amp).
-- Mode, cutoff, Q, and mod-amt controls appear in a filter deck group; the
+- Mode, cutoff, Q, and mod-amt controls appear in a deck group labeled
-  filter AHDSR gets the full item-1 treatment (curve inner dials, corner radio
+  **"Filter"**; the filter AHDSR gets the full item-1 treatment (curve inner
-  switch, tertiary-purple overlay editing).
+  dials, corner radio switch, tertiary-purple overlay editing).
+- Cutoff sweeps the full audio spectrum on a log scale, from fully open to
+  fully closed; Q spans 0.1 → 10 with √2 at the control's center; mod amt at
+  −100% and at +100% each drive cutoff across the full range, from opposite
+  ends.
 - High Q audibly emphasizes the cutoff region (resonance) in both HP and LP
   modes.
+- Two simultaneously sounding voices at different envelope phases are filtered
+  independently (per-voice processing is audible, not a shared instance-wide
+  filter).
 - The deck row reads pitch → filter → amp left-to-right.
 - A project saved before this change reopens sounding identical (pending the
   neutral-default confirmation above).
@@ -180,6 +222,15 @@ AHDSR envelope, and make the knob-deck row read in signal-flow order.
 > for the velocity-amp transfer curve as well as the pitch, filter, and amp EGs
 > (if they are in spline mode).
 
+**Daniel's follow-up (verbatim, 2026-07-28).**
+
+> dual state, save but inactive. Default Curve Spline is a smooth y=1-x. Gate
+> mode is not available when the Spline is used, spline always covers the full
+> sample length. The spline curves don't have to rise AND fall, they also
+> aren't globally monotone, the default curve is a smooth downward slope over
+> the length. all the soft points between any hard points will be
+> smooth/monotone.
+
 **Intent.** Offer a free-drawn alternative to every staged envelope: the user
 switches any EG from Staged to Spline mode and draws the contour directly, with
 the monotonic-spline machinery already proven by the velocity curve — enhanced
@@ -189,6 +240,22 @@ so sharp corners are possible, not everything smoothed.
 
 - **Mode toggle per EG.** Every processor that has an envelope (pitch, filter,
   amp) can switch its Staged EG to a **Spline EG**.
+- **Dual state — save but inactive.** Both the Staged and the Spline state are
+  persisted; switching modes keeps the inactive one **saved but inactive**. No
+  conversion, no discard — round-tripping Staged↔Spline restores the other
+  mode's shape untouched. *(Settled by follow-up.)*
+- **Gate unavailable in Spline mode.** Gate mode is **not available while a
+  Spline EG is active**; the spline **always covers the full sample length** —
+  a pure time function over the sample, i.e. the Trigger/one-shot playback
+  model. *(Settled by follow-up.)*
+- **Not globally monotone.** Spline contours **don't have to rise and fall and
+  are not globally monotone**; the monotone guarantee is per-segment — **all
+  soft points between any hard points are smooth/monotone** (no overshoot
+  between adjacent points). *(Settled by follow-up.)*
+- **Default contour.** A new Spline EG defaults to a **smooth y = 1 − x** — a
+  smooth downward slope over the full sample length. (Read as the Spline-EG
+  default contour; not a change to the velocity→amp transfer curve's existing
+  default.) *(Settled by follow-up.)*
 - **Spline foundation.** The Spline EG is based on the monotonic splines used
   for the velocity curve. The spline algorithm is singly implemented and
   multi-referenced; the enhancement below applies to that one implementation
@@ -210,30 +277,17 @@ so sharp corners are possible, not everything smoothed.
 
 **Open questions.**
 
-- **Staged↔Spline toggle semantics.** What happens to a Staged EG's values
+- **Time-axis storage.** Full-sample coverage is settled ("spline always
-  when toggling to Spline mode and back? (Convert the staged shape into an
+  covers the full sample length"); what remains is only whether the stored
-  initial spline? Keep two independent per-mode states? Discard?) Daniel has
+  contour is normalized to the sample length (so it rescales when a
-  not said — this materially shapes both UX and persistence and needs his
+  different-length capture loads) or anchored some other way.
-  call.
-- **Gate-mode sustain/release.** A Staged Gate envelope holds at Sustain and
-  releases on note-off; a spline contour drawn "over the full sample length"
-  is a pure time function. How do note-off, sustain, and looped playback map
-  onto a Spline EG in Gate mode? (Trigger/one-shot is the natural fit; Gate
-  needs a stated rule.)
-- **Time axis.** Is the contour's time axis normalized to the sample length
-  (so it rescales with the sample) or absolute seconds? "Over the full sample
-  length" suggests sample-relative — confirm, especially for looped sustain.
-- **Monotonicity meaning.** The velocity spline is monotone to prevent
-  overshoot on a transfer curve. An EG contour must rise and fall; presumably
-  "monotonic" here means the per-segment no-overshoot property (values never
-  exceed the segment's endpoints), not a globally monotone function — confirm
-  the intended guarantee.
 - **Point-editing grammar.** Point add/delete gestures and any point-count
   bound are unstated. The velocity-curve popup already established right-click
   node delete — reuse of that grammar seems natural but is Daniel's call.
-- **Interaction with item-1 curve dials.** In Spline mode, do the staged
+- **Staged controls while Spline is active.** Sound-wise the staged EG is
-  segment knobs/inner dials go inert (shape comes wholly from the spline), or
+  inactive in Spline mode (settled by dual-state). Still open at the UI level:
-  is some hybrid intended? Presumably the former — confirm.
+  do the staged segment knobs/inner dials stay editable (editing the dormant
+  staged state) or go inert/greyed until the user switches back?
 
 **Acceptance criteria.**
 
@@ -245,8 +299,14 @@ so sharp corners are possible, not everything smoothed.
   adjacent segment, and the discontinuous slope is audible where the
   modulation target makes it so (e.g. a pitch EG corner).
 - A contour of several segments joined at hard points plays back over the full
-  sample length exactly as drawn.
+  sample length exactly as drawn — including contours that rise and fall
+  freely (no globally-monotone restriction), with no overshoot between any
+  adjacent pair of points.
+- A freshly created Spline EG shows the smooth y = 1 − x default contour.
+- While a Spline EG is active, Gate mode is not selectable; the spline plays
+  as a pure time function over the full sample length.
+- Staged↔Spline round-trip preserves both states: switch to Spline, draw,
+  switch back — the staged values are exactly as left; switch forward again —
+  the spline contour is exactly as drawn. Both survive save/reload.
 - The velocity→amp transfer-curve editor supports the same control-click
   hard/smooth toggle with identical rendering behavior.
-- Staged↔Spline toggling behaves per the answered open question above (that
-  answer gates this item's completion definition).