S-VIEW-9: velocity->amp transfer curve (pure velocity_curve module + zones-payload v7 + Voice::start apply)

Default flat y=1 (R10-F1 Option A) replaces the linear velocity/127 at note-on — a deliberate, non-back-compat behavior change; v1-v6 blobs lift to the flat default.

tests/test_sampler_core.cpp

@@ -422,6 +422,10 @@ static void testNoteOffReleasesNewestSameNote() {
     sd.play.adsr = flatAdsr();
     sd.play.adsr.releaseFrames = 10;   // short but non-zero so voice stays active through release
     Keymap km = Keymap::singleSampleChromatic(sd);
+    // A LINEAR velocity curve keeps the two velocities distinguishable (velocity/127). The default
+    // flat y=1 curve (S-VIEW-9 R10-F1) would render both at unity, collapsing the distinction this
+    // note-off-selection test relies on — so we opt this zone back to the linear response.
+    km.zones[0].velocityCurve = vst::VelocityCurve::linear();
     VoiceEngine eng(8, km);
 
     std::size_t first  = eng.noteOn(60, velOld);  // older voice, lower gain
@@ -728,33 +732,60 @@ static void testStartAfterLoopEndWrapsIntoLoop() {
 // velocity -> volume.
 // ---------------------------------------------------------------------------
 
-static void testVelocityToVolume() {
+// S-VIEW-9 BEHAVIOR CHANGE (R10-F1 Option A): the DEFAULT velocity curve on a KeyZone is now flat
+// y=1, so EVERY velocity plays at unity — NOT the old linear velocity/127. singleSampleChromatic
+// builds a zone with the flat default, so the DC-1 sample renders 1.0 at any velocity.
+static void testVelocityDefaultCurveIsFlatUnity() {
+    Keymap km = Keymap::singleSampleChromatic(dcSample(100, 60));  // DC 1.0, flat default curve
+    for (int vel : {1, 64, 100, 127}) {
+        VoiceEngine eng(1, km);
+        eng.noteOn(60, vel);
+        std::vector<AudioSample> out;
+        eng.render(out, 1);
+        CHECK(approx(out[0], 1.0, 1e-4));  // flat y=1: any velocity -> unity gain
+    }
+}
+
+// A LINEAR curve on the zone reproduces the pre-r10 velocity/127 ramp exactly — proving the curve
+// (not a hardcoded map) drives the gain, and that eval is applied at note-on.
+static void testVelocityLinearCurveReproducesRamp() {
     Keymap km = Keymap::singleSampleChromatic(dcSample(100, 60));  // DC 1.0
-    // Full velocity -> full gain; half velocity -> ~half gain (flat envelope so the
-    // rendered value is exactly velocity/127 on a DC-1 sample).
+    km.zones[0].velocityCurve = vst::VelocityCurve::linear();
     {
         VoiceEngine eng(1, km);
         eng.noteOn(60, 127);
-        std::vector<AudioSample> out;
-        eng.render(out, 1);
+        std::vector<AudioSample> out; eng.render(out, 1);
         CHECK(approx(out[0], 1.0, 1e-4));
     }
     {
         VoiceEngine eng(1, km);
         eng.noteOn(60, 64);
-        std::vector<AudioSample> out;
-        eng.render(out, 1);
+        std::vector<AudioSample> out; eng.render(out, 1);
         CHECK(approx(out[0], 64.0 / 127.0, 1e-4));
     }
     {
         VoiceEngine eng(1, km);
         eng.noteOn(60, 1);
-        std::vector<AudioSample> out;
-        eng.render(out, 1);
+        std::vector<AudioSample> out; eng.render(out, 1);
         CHECK(approx(out[0], 1.0 / 127.0, 1e-4));
     }
 }
 
+// A shaped curve (a single interior knot) drives the gain through eval — a mid velocity reads the
+// curve's shaped value, not the linear one. Proves the whole curve, not just the endpoints, applies.
+static void testVelocityShapedCurveDrivesGain() {
+    Keymap km = Keymap::singleSampleChromatic(dcSample(100, 60));  // DC 1.0
+    vst::VelocityCurve curve = vst::VelocityCurve::linear();
+    curve.addPoint(64.0, 0.9);  // pull the mid-velocity response UP to 0.9
+    km.zones[0].velocityCurve = curve;
+    VoiceEngine eng(1, km);
+    eng.noteOn(60, 64);
+    std::vector<AudioSample> out; eng.render(out, 1);
+    // At exactly velocity 64 the curve passes through the knot -> gain 0.9 (well above the linear
+    // 64/127 ~= 0.504), so the rendered DC value is the shaped 0.9.
+    CHECK(approx(out[0], 0.9, 1e-4));
+}
+
 // Two voices summed: polyphony mixes additively.
 static void testPolyphonyMixesAdditively() {
     Keymap km = Keymap::singleSampleChromatic(dcSample(100, 60));  // DC 1.0
@@ -1348,7 +1379,9 @@ int main() {
     testStartFrameOutOfRangeClampsToZero();
     testStartFrameWithLoop();
     testStartAfterLoopEndWrapsIntoLoop();
-    testVelocityToVolume();
+    testVelocityDefaultCurveIsFlatUnity();
+    testVelocityLinearCurveReproducesRamp();
+    testVelocityShapedCurveDrivesGain();
     testPolyphonyMixesAdditively();
     testChannelCount();
     testStereoRenderKeepsChannelsDistinct();