fix(synth): Implement peak meter with decay for smooth visuals

The graphics appeared static because the audio peak value was transient, only lasting for a single audio buffer. The main graphics loop, running much faster, would mostly read a zero value.

This fix implements a simple peak meter with an exponential decay. The peak value now rises instantly to the maximum sample value but fades out smoothly over several frames, providing a persistent and smooth value for the visualizer.

1 files changed, 6 insertions, 5 deletions

diff --git a/src/audio/synth.cc b/src/audio/synth.cc
index 98c12d9..77a0d05 100644
--- a/src/audio/synth.cc
+++ b/src/audio/synth.cc
@@ -26,7 +26,7 @@ static struct {
 } g_synth_data;
 
 static Voice g_voices[MAX_VOICES];
-static float g_current_output_peak = 0.0f; // Global peak for visualization
+static volatile float g_current_output_peak = 0.0f; // Global peak for visualization
 
 void synth_init() {
   memset(&g_synth_data, 0, sizeof(g_synth_data));
@@ -125,7 +125,8 @@ void synth_render(float *output_buffer, int num_frames) {
   float window[WINDOW_SIZE];
   hamming_window_512(window);
 
-  float current_peak_in_frame = 0.0f;
+  // Apply a decay to the peak value for smooth visuals
+  g_current_output_peak *= 0.95f;
 
   for (int i = 0; i < num_frames; ++i) {
     float left_sample = 0.0f;
@@ -170,10 +171,10 @@ void synth_render(float *output_buffer, int num_frames) {
     output_buffer[i * 2] = left_sample;
     output_buffer[i * 2 + 1] = right_sample;
 
-    current_peak_in_frame =
-        fmaxf(current_peak_in_frame, fmaxf(fabsf(left_sample), fabsf(right_sample)));
+    // Update the peak with the new max (attack)
+    g_current_output_peak =
+        fmaxf(g_current_output_peak, fmaxf(fabsf(left_sample), fabsf(right_sample)));
   }
-  g_current_output_peak = current_peak_in_frame;
 }
 
 int synth_get_active_voice_count() {