Feature: frequency modulation MVP implemented :loud-sound:

2 files changed, 63 insertions, 31 deletions

diff --git a/klangfarb/main.gd b/klangfarb/main.gd
index 95c0f8f..4397a7e 100644
--- a/klangfarb/main.gd
+++ b/klangfarb/main.gd
@@ -18,11 +18,16 @@ export(float, 0.0, 1.0, 0.1) var sustain = 0.5
 #Cutoff
 export(float, 20, 8000, 5) var cutoff = 6000
 
+# Frequency Modulation
+export(bool) var frequency_modulation = false
+export(float, 0.0, 100.0, 0.1) var fm_frequency = 1.0
+export(float, 0.0, 10.0, 0.1) var fm_amplitude = 0.1
+
 # load the GDNative script connected to the rust lib
 var MonoSynth = preload("res://MonoSynth.gdns")
 
 # make an instance of our one "class" in rust lib
-var wave = MonoSynth.new()
+var synth = MonoSynth.new()
 
 # initialize the Godot stream we fill up with samples
 var playback: AudioStreamPlayback = null
@@ -32,25 +37,28 @@ func _fill_buffer() -> void:
 	var to_fill = playback.get_frames_available()
 	if to_fill > 0:
 		# ask Rust to generate N frames at freq
-		# Array<Vector2> gets pushed to the 
+		# Array<Vector2> gets pushed to the
 		# playback stream buffer
-		playback.push_buffer(wave.frames(to_fill)) 
+		playback.push_buffer(synth.frames(to_fill))
 
 func _check_waveform():
 	if waveform == "square":
-		wave.square()
+		synth.square()
 	elif waveform == "sine":
-		wave.sine()
+		synth.sine()
 	elif waveform == "triangle":
-		wave.triangle()
+		synth.triangle()
 	elif waveform == "sawtooth":
-		wave.sawtooth()
+		synth.sawtooth()
 
 func _process(_delta):
 	if self.is_playing():
-		wave.apply_bend(apply_bend)		
-		wave.frequency(freq)
-		wave.phasor_bend(phasor_bend)
+		synth.apply_bend(apply_bend)
+		synth.frequency(freq) 
+		synth.phasor_bend(phasor_bend)
+		synth.frequency_modulation(frequency_modulation)
+		synth.fm_frequency(fm_frequency)
+		synth.fm_depth(fm_amplitude)
 		_check_waveform()
 		_fill_buffer()
 
@@ -58,7 +66,7 @@ func _ready() -> void:
 	# buffer length of 100ms gives us ~realtime response to input changes
 	self.stream.buffer_length = 0.1
 	# ensure Godot/Sine have the same sample rate
-	wave.set_sample_rate(self.stream.mix_rate)
+	synth.set_sample_rate(self.stream.mix_rate)
 	# get our AudioStreamPlayback object
 	playback = self.get_stream_playback()
 	# prefill the stream's sample buffer (which feeds DAC)
@@ -70,6 +78,6 @@ func _input(event):
 	if event is InputEventMouseButton:
 		print("Mouse Click/Unclick at: ", event.position)
 	elif event is InputEventMouseMotion:
-#		freq = event.position.x
-		phasor_bend.x = event.position.x / 1024
-		phasor_bend.y = event.position.y / 600
+		freq = event.position.x
+#		phasor_bend.x = event.position.x / 1024
+#		phasor_bend.y = event.position.y / 600
diff --git a/klangfarbrs/src/lib.rs b/klangfarbrs/src/lib.rs
index 479885c..07e9cc7 100644
--- a/klangfarbrs/src/lib.rs
+++ b/klangfarbrs/src/lib.rs
@@ -11,14 +11,15 @@ use gdnative::prelude::*;
 use gdnative::core_types::TypedArray;
 use std::f32::consts::TAU;
 
+/// Aliasing some types to distinguish various audio properties.
 type Sample = f32;
-type Samples = f32;
+type SamplesPerSecond = f32;
 type Hz = f32;
 type Phase = f32;
 type Amplitude = f32;
 type Millisecond = u32;
 
-/// The various waveforms the `Synth` can generate.
+/// The various waveforms the `MonoSynth` can generate.
 pub enum Waveform {
     Sine,
     Square,
@@ -32,30 +33,25 @@ pub enum Waveform {
 pub struct MonoSynth {
     pub phasor: Phasor,
     pub waveform: Waveform,
-    #[property]
-    pub sample_rate: Samples,
-    #[property]
+    pub sample_rate: SamplesPerSecond,
     pub frequency: Hz,
-    #[property]
     pub apply_bend: bool,
-    #[property]
     pub phasor_bend: Vector2,
-    #[property]
     pub continuous: bool,
-    #[property]
     pub duration: Millisecond,
-    #[property]
+    // ADSR amplifier
     pub attack: Millisecond,
-    #[property]
     pub decay: Millisecond,
-    #[property]
     pub sustain: Amplitude,
-    #[property]
     pub release: Millisecond,
-    #[property]
+    // filter
     pub cutoff: Hz,
     // pub resonance:
     // pub modulator:
+    pub frequency_modulation: bool,
+    pub fm_frequency: Hz,
+    pub fm_depth: Amplitude,
+    fm_phasor: Phasor,
 }
 
 pub struct Osc {}
@@ -101,7 +97,7 @@ impl Phasor {
     /// for a given wave form. Since audio signals are periodic, we can just calculate
     /// the first cycle of a wave repeatedly. This also prevents pitch drift caused by
     /// floating point errors over time.
-    pub fn next_phase(&self, frequency: Hz, sample_rate: Samples ) -> Phase {
+    pub fn next_phase(&self, frequency: Hz, sample_rate: SamplesPerSecond ) -> Phase {
         (self.phase + (frequency / sample_rate)) % 1.0
     }
 }
@@ -160,6 +156,10 @@ impl MonoSynth {
             sustain: 0.0,
             release: 0,
             cutoff: 0.0,
+            frequency_modulation: false,
+            fm_frequency: 30000.0,
+            fm_depth: 0.1,
+            fm_phasor: Phasor { phase: 0.0 }
         }
     }
 
@@ -209,19 +209,43 @@ impl MonoSynth {
     }
 
     #[export]
+    fn frequency_modulation(&mut self, _owner: &Node, frequency_modulation: bool) {
+        self.frequency_modulation = frequency_modulation
+    }
+
+    #[export]
+    fn fm_frequency(&mut self, _owner: &Node, fm_frequency: f32) {
+        self.fm_frequency = fm_frequency
+    }
+
+    #[export]
+    fn fm_depth(&mut self, _owner: &Node, fm_depth: f32) {
+        self.fm_depth = fm_depth
+    }
+
+    #[export]
     pub fn frames(&mut self, _owner: &Node, samples: i32) -> TypedArray<Vector2> {
         let mut frames = TypedArray::new();
 
         for _i in 0..samples {
             let sample = Osc::generate_sample(&self.waveform, self.phasor.phase);
-            frames.push(Vector2::new(sample, sample));
+            let next_phase : f32;
+
+            if self.frequency_modulation {
+                let modulation_value = Osc::generate_sample(&Waveform::Sine, self.fm_phasor.phase) * self.fm_depth;
+                self.fm_phasor.phase = self.fm_phasor.next_phase(self.fm_frequency, self.sample_rate);
+                next_phase = self.phasor.next_phase(self.frequency * modulation_value, self.sample_rate);
+            } else {
+                next_phase = self.phasor.next_phase(self.frequency, self.sample_rate);
+            }
 
-            let next_phase = self.phasor.next_phase(self.frequency, self.sample_rate);
             if self.apply_bend {
                 self.phasor.phase = Bender::bend(next_phase, self.phasor_bend);
             } else {
                 self.phasor.phase = next_phase;
             }
+
+            frames.push(Vector2::new(sample, sample));
         }
 
         return frames