Piano: Make decay more accurate

1. Make decay sample-granular rather than buffer-granular
You only have ~43 buffers per second which can make a jagged signal.

2. Calculate decay in milliseconds
Decay is supposed to be a time value.

3 files changed, 21 insertions, 12 deletions

diff --git a/Applications/Piano/AudioEngine.cpp b/Applications/Piano/AudioEngine.cpp
index 15fe0ac609..3378ebaf07 100644
--- a/Applications/Piano/AudioEngine.cpp
+++ b/Applications/Piano/AudioEngine.cpp
@@ -31,6 +31,7 @@
 
 AudioEngine::AudioEngine()
 {
+    set_decay(0);
 }
 
 AudioEngine::~AudioEngine()
@@ -45,6 +46,11 @@ void AudioEngine::fill_buffer(FixedArray<Sample>& buffer)
         for (size_t note = 0; note < note_count; ++note) {
             if (!m_note_on[note])
                 continue;
+
+            m_power[note] -= m_decay_step;
+            if (m_power[note] < 0)
+                m_power[note] = 0;
+
             double val = 0;
             switch (m_wave) {
             case Wave::Sine:
@@ -70,16 +76,6 @@ void AudioEngine::fill_buffer(FixedArray<Sample>& buffer)
         buffer[i].right = buffer[i].left;
     }
 
-    if (m_decay) {
-        for (size_t note = 0; note < note_count; ++note) {
-            if (m_note_on[note]) {
-                m_power[note] -= m_decay / 100.0;
-                if (m_power[note] < 0)
-                    m_power[note] = 0;
-            }
-        }
-    }
-
     if (m_delay) {
         if (m_delay_buffers.size() >= m_delay) {
             auto to_blend = m_delay_buffers.dequeue();
@@ -201,10 +197,22 @@ void AudioEngine::set_wave(Direction direction)
     }
 }
 
+static inline double calculate_step(double distance, int milliseconds)
+{
+    if (milliseconds == 0)
+        return distance;
+
+    constexpr double samples_per_millisecond = sample_rate / 1000.0;
+    double samples = milliseconds * samples_per_millisecond;
+    double step = distance / samples;
+    return step;
+}
+
 void AudioEngine::set_decay(int decay)
 {
     ASSERT(decay >= 0);
     m_decay = decay;
+    m_decay_step = calculate_step(1, m_decay);
 }
 
 void AudioEngine::set_delay(int delay)
diff --git a/Applications/Piano/AudioEngine.h b/Applications/Piano/AudioEngine.h
index 14280a716f..4f5bdc1585 100644
--- a/Applications/Piano/AudioEngine.h
+++ b/Applications/Piano/AudioEngine.h
@@ -77,7 +77,8 @@ private:
 
     int m_octave { 4 };
     int m_wave { first_wave };
-    int m_decay { 0 };
+    int m_decay;
+    double m_decay_step;
     int m_delay { 0 };
 
     int m_time { 0 };
diff --git a/Applications/Piano/KnobsWidget.cpp b/Applications/Piano/KnobsWidget.cpp
index 4ec786ebad..caa9c40cec 100644
--- a/Applications/Piano/KnobsWidget.cpp
+++ b/Applications/Piano/KnobsWidget.cpp
@@ -91,7 +91,7 @@ KnobsWidget::KnobsWidget(GUI::Widget* parent, AudioEngine& audio_engine, MainWid
         m_wave_value->set_text(wave_strings[new_wave]);
     };
 
-    constexpr int max_decay = 20;
+    constexpr int max_decay = 1000;
     m_decay_knob = GUI::Slider::construct(Orientation::Vertical, m_knobs_container);
     m_decay_knob->set_range(0, max_decay);
     m_decay_knob->set_value(max_decay - m_audio_engine.decay());