diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0ce08f5..dee1fba 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -27,6 +27,11 @@ FetchContent_Declare(
     GIT_REPOSITORY  https://github.com/hyperrealm/libconfig.git
     GIT_TAG         v1.8.2
 )
+FetchContent_Declare(
+    eigen
+    GIT_REPOSITORY  git@gitlab.com:libeigen/eigen.git
+    GIT_TAG         5.0
+)
 FetchContent_MakeAvailable(rtaudio)
 FetchContent_MakeAvailable(rtmidi)
 FetchContent_MakeAvailable(libconfig)
diff --git a/README.md b/README.md
index 02fc744..f614f9d 100644
--- a/README.md
+++ b/README.md
@@ -29,7 +29,7 @@ to produce somewhat well-sounding instruments and music performance.
       to external midi controllers/apps (like musescore)
 - [ ] Create a UI scope to visualize the synthesized composite waveform
 - [ ] Check cross-platform combatibility for Windows & Linux, especially MIDI interfacing
-- [ ] Checkpoint at a rudimentary keyboard instrument producing a basic sine output
+- [x] Checkpoint at a rudimentary keyboard instrument producing a basic sine output
 - [ ] Will flesh out future goals when I do the math on how complicated implementing
       state-space modelling in c++ is
 
diff --git a/src/synth/Instrument.cpp b/src/synth/Instrument.cpp
index cd51a0c..09ba614 100644
--- a/src/synth/Instrument.cpp
+++ b/src/synth/Instrument.cpp
@@ -10,11 +10,10 @@ Instrument::Instrument(ConfigService* config, LoggerService* logger) :
 
 void Instrument::noteOn(float frequency, float velocity) {
 
-    // std::string msg = "NoteOn Frequency = " + std::to_string(frequency);
-    // if(logger_ != nullptr) logger_->log("Instrument", LogFlag::Debug, msg);
-
     phaseIncrement_ = 2.0f * pi * frequency / sampleRate_;
 
+    envelope_ += 0.01f; // so it triggers as active
+
     active_ = true;
 }
 
@@ -23,14 +22,18 @@ void Instrument::noteOff() {
 }
 
 bool Instrument::isActive() {
-    return active_;
+    return (envelope_ > 0.0f);
 }
 
 float Instrument::process(bool& scopeTrigger) {
 
+    if(active_ && envelope_ < 1.0f) envelope_ += 0.01f;
+    if(!active_ && envelope_ > 0.0f) envelope_ -= 0.01f;
+
     phase_ += phaseIncrement_;
     if(phase_ > 2.0f * pi) phase_ -= 2.0f * pi;
 
-    return sin(phase_);
+    if(!isActive()) return 0.0f;
+    return sin(phase_) * envelope_;
 
 }
diff --git a/src/synth/Instrument.hpp b/src/synth/Instrument.hpp
index fbb9118..7ccc6a7 100644
--- a/src/synth/Instrument.hpp
+++ b/src/synth/Instrument.hpp
@@ -32,5 +32,6 @@ private:
     static constexpr float pi = 3.14159265358979323846f;
     float phase_ = 0.0f;
     float phaseIncrement_ = 0.0f;
+    float envelope_ = 0.0f;
 
 };
diff --git a/src/synth/Synth.cpp b/src/synth/Synth.cpp
index a5790df..154aa52 100644
--- a/src/synth/Synth.cpp
+++ b/src/synth/Synth.cpp
@@ -45,7 +45,7 @@ void Synth::process(float* out, size_t nFrames) {
         float mix = 0.0f;
         for(size_t j = 0; j < voices_.size(); j++) {
             bool temp = false;
-            if(!voices_[j].isActive()) continue;
+            //if(!voices_[j].isActive()) continue;
             mix += voices_[j].process(temp);
             // if(j == lowestVoice) triggered = temp;
         }