Merge pull request #50 from 223230/feature-peak-buffer-decay

Peak Buffer decay

examples/visualizers/src/lib.rs

@@ -36,7 +36,7 @@ impl Default for VisualizersDemo {
         Self {
             params: Arc::new(DemoParams::default()),
             oscilloscope_buffer: Arc::new(Mutex::new(WaveformBuffer::new(800, 44100.0, 5.0))),
-            peak_buffer: Arc::new(Mutex::new(PeakBuffer::new(800, 44100.0, 10.0))),
+            peak_buffer: Arc::new(Mutex::new(PeakBuffer::new(800, 10.0, 50.))),
             lissajous_buffer: Arc::new(Mutex::new(RingBuffer::new(2048))),
 
             spectrum_input,

src/utils/buffers/peak_buffer.rs

@@ -14,35 +14,56 @@ pub struct PeakBuffer {
     duration: f32,
     // The current time, counts down from sample_delta to 0
     t: f32,
+    /// The decay time for the peak amplitude to halve.
+    decay: f32,
+    // This is set `set_sample_rate()` based on the sample_delta
+    decay_weight: f32,
 }
 
 impl PeakBuffer {
-    pub fn new(size: usize, sample_rate: f32, duration: f32) -> Self {
-        let sample_delta = Self::sample_delta(size, sample_rate as f32, duration as f32);
+    pub fn new(size: usize, duration: f32, decay: f32) -> Self {
+        let decay_weight = Self::decay_weight(decay, size, duration);
         Self {
             buffer: RingBuffer::<f32>::new(size),
             max_acc: 0.,
-            sample_delta,
-            sample_rate,
+            sample_delta: 0.,
+            sample_rate: 0.,
             duration,
-            t: sample_delta,
+            t: 0.,
+            decay,
+            decay_weight,
         }
     }
 
+    pub fn set_decay(self: &mut Self, decay: f32) {
+        self.decay = decay;
+        self.update();
+    }
+
     pub fn set_sample_rate(self: &mut Self, sample_rate: f32) {
         self.sample_rate = sample_rate;
-        self.sample_delta = Self::sample_delta(self.buffer.len(), sample_rate, self.duration);
+        self.update();
         self.buffer.clear();
     }
 
     pub fn set_duration(self: &mut Self, duration: f32) {
         self.duration = duration;
-        self.sample_delta = Self::sample_delta(self.buffer.len(), self.sample_rate, duration);
+        self.update();
         self.buffer.clear();
     }
 
     fn sample_delta(size: usize, sample_rate: f32, duration: f32) -> f32 {
-        (sample_rate * duration) / size as f32
+        ((sample_rate as f64 * duration as f64) / size as f64) as f32
+    }
+
+    fn decay_weight(decay: f32, size: usize, duration: f32) -> f32 {
+        0.25f64.powf((decay as f64 / 1000. * (size as f64 / duration as f64)).recip()) as f32
+    }
+
+    fn update(self: &mut Self) {
+        self.decay_weight = Self::decay_weight(self.decay, self.buffer.len(), self.duration);
+        self.sample_delta = Self::sample_delta(self.buffer.len(), self.sample_rate, self.duration);
+        self.t = self.sample_delta;
     }
 }
 
@@ -51,7 +72,17 @@ impl VisualizerBuffer<f32> for PeakBuffer {
         let value = value.abs();
         self.t -= 1.0;
         if self.t < 0.0 {
-            self.buffer.enqueue(self.max_acc);
+            let last_peak = self.buffer.peek();
+            let mut peak = self.max_acc;
+
+            // If the current peak is greater than the last one, we immediately enqueue it. If it's less than
+            // the last one, we weigh the previous into the current one, analogous to how peak meters work.
+            self.buffer.enqueue(if peak >= last_peak {
+                peak
+            } else {
+                (last_peak * self.decay_weight) + (peak * (1.0 - self.decay_weight))
+            });
+
             self.t += self.sample_delta;
             self.max_acc = 0.;
         }
@@ -95,7 +126,7 @@ impl VisualizerBuffer<f32> for PeakBuffer {
             return;
         };
         self.buffer.grow(size);
-        self.sample_delta = Self::sample_delta(size, self.sample_rate, self.duration);
+        self.update();
         self.buffer.clear();
     }
 
@@ -105,7 +136,7 @@ impl VisualizerBuffer<f32> for PeakBuffer {
             return;
         };
         self.buffer.shrink(size);
-        self.sample_delta = Self::sample_delta(size, self.sample_rate, self.duration);
+        self.update();
         self.buffer.clear();
     }
 }
@@ -122,22 +153,3 @@ impl IndexMut<usize> for PeakBuffer {
         self.buffer.index_mut(index)
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use crate::utils::VisualizerBuffer;
-
-    use super::PeakBuffer;
-
-    #[test]
-    fn enqueue() {
-        let mut rb = PeakBuffer::new(16, 4.0, 8.0);
-
-        rb.enqueue(2.);
-        rb.enqueue(9.);
-        rb.enqueue(19.);
-        rb.enqueue(-10.);
-        rb.enqueue(4.);
-        rb.enqueue(6.);
-    }
-}

src/utils/buffers/ring_buffer.rs

@@ -96,6 +96,10 @@ impl<T: Default + Copy> RingBuffer<T> {
         self.head = (self.head + 1) % self.size;
     }
 
+    pub fn peek(self: &Self) -> T {
+        self.data[(self.size + self.head - 1) % self.size]
+    }
+
     /// Clears the entire buffer, filling it with default values (usually 0)
     pub fn clear(self: &mut Self) {
         self.data.iter_mut().for_each(|x| *x = T::default());
@@ -271,4 +275,20 @@ mod tests {
 
         rb[4];
     }
+
+    #[test]
+    fn peek() {
+        let mut rb = RingBuffer::<i32>::new(4);
+
+        rb.enqueue(1);
+        assert_eq!(rb.peek(), 1);
+        rb.enqueue(2);
+        rb.enqueue(3);
+        assert_eq!(rb.peek(), 3);
+        rb.enqueue(4);
+        rb.enqueue(5);
+        rb.enqueue(6);
+        rb.enqueue(7);
+        assert_eq!(rb.peek(), 7);
+    }
 }