Trigger the track env (which trigger the instrument)

pros:
* same env on each track
* instrument can be drone, but can also react to trig

cons:
* instrument can only shorten the decay, its limited by the track env

src/main_perkons.cc

@@ -293,7 +293,7 @@ namespace Heck {
         switch (msg.type) {
             case ld::MidiMessageType::NoteOn: {
                 if (msg.channel >= 0 && msg.channel < Constants::TRACK_COUNT) {
-                    tracks[msg.channel].instrument->trigger();
+                    tracks[msg.channel].trigger();
                 }
             } break;
             case ld::MidiMessageType::ControlChange: {
@@ -312,7 +312,7 @@ namespace Heck {
                         tracks[cc.channel].instrument->ctl(2, val_normalized);
                         break;
                     case Constants::MIDI_Mapping::TRACK_PARAM2:
-                        tracks[cc.channel].instrument->ctl(3, val_normalized);
+                        tracks[cc.channel].decay(val_normalized);
                         break;
                     case Constants::MIDI_Mapping::TRACK_FILTER:
                         tracks[cc.channel].filter(val_normalized);

src/track.hh

@@ -11,26 +11,52 @@ namespace Heck {
     public:
         void init(Instrument::AbstractInstrument& instr)
         {
+            // Instr
             instrument.reset(&instr);
+
+            // Env
+            decay_.Init(Constants::SAMPLERATE);
+            decay_.SetTime(dsp::ADENV_SEG_ATTACK, .0001);
+            decay_.SetTime(dsp::ADENV_SEG_DECAY, 0.1);
+            decay_.SetMax(1);
+            decay_.SetMin(0);
+            decay_.SetCurve(-18);
+
+            // Vol
             ctl_volume_ = 0.;
 
+            // Filter
             ladder_.Init(Constants::SAMPLERATE);
             ladder_.SetFilterMode(daisysp::LadderFilter::FilterMode::LP24);
             ladder_.SetRes(0.7);
             ladder_.SetInputDrive(1.3);
 
+            // Drive
             od_.Init();
         }
 
         float nextsample()
         {
             float sig = instrument->nextsample();
+            float vol_env_sig = decay_.Process();
+            sig *= vol_env_sig;
             sig = ladder_.Process(sig);
             sig = od_.Process(sig);
             sig = vca_(sig, ctl_volume_);
             return sig;
         }
 
+        void trigger()
+        {
+            decay_.Trigger();
+            instrument->trigger();
+        }
+
+        void decay(float val)
+        {
+            decay_.SetTime(dsp::ADENV_SEG_DECAY, 0.01 + val * 8.);
+        }
+
         void volume(float vol)
         {
             ctl_volume_ = vol;
@@ -69,6 +95,7 @@ namespace Heck {
         std::shared_ptr<Instrument::AbstractInstrument> instrument{};
 
     private:
+        dsp::AdEnv decay_{};
         dsp::LinearVCA vca_{};
         dsp::LadderFilter ladder_{};
         dsp::Overdrive od_{};