Increase realtime display transport rate

scripts/test_websocket_runtime.mjs

@@ -37,5 +37,5 @@ metrics.addEventListener('message', (event) => {
 await new Promise((resolve) => setTimeout(resolve, 1100));
 sockets.forEach((socket) => socket.close());
 assert.equal(invalidPayload, false, 'metrics must be ordered and contain no large visual payloads');
-assert.ok(count >= 50 && count <= 75, `expected about 60 metrics/s, received ${count}`);
+assert.ok(count >= 110 && count <= 145, `expected about 120 metrics/s, received ${count}`);
 console.log(`runtime websocket test passed (${count} metrics in 1.1 s; max frame age ${maxFrameAgeMs} ms; all three streams opened)`);

src/audio.rs

@@ -40,8 +40,12 @@ use crate::{
     model::{InputSource, MeterFrame, PhoenixRtaConfig},
 };
 
-#[cfg(target_os = "linux")]
+// Keep transport sampling safely above the 60 Hz display cadence. ALSA only
-const METRICS_TARGET_UPDATES_PER_SECOND: u32 = 60;
+// exposes complete capture periods, so a 60 Hz target with 128-frame periods
+// alternates between roughly 16.0 and 18.7 ms at 48 kHz. A 120 Hz snapshot
+// clock guarantees at least one fresh native state per display frame without
+// changing any detector or ballistic calculation.
+const METRICS_TARGET_UPDATES_PER_SECOND: u32 = 120;
 
 #[derive(Clone, Copy, Debug, Default)]
 struct TransportPeaks {
@@ -415,7 +419,8 @@ pub fn spawn_audio_capture_worker(deps: AudioWorkerDeps) {
 pub fn spawn_audio_capture_worker(deps: AudioWorkerDeps) {
     tokio::spawn(async move {
         warn!("Phoenix ALSA capture is only available on Linux; emitting placeholder frames on this host");
-        let mut ticker = tokio::time::interval(Duration::from_millis(16));
+        let tick_ns = 1_000_000_000u64 / u64::from(METRICS_TARGET_UPDATES_PER_SECOND);
+        let mut ticker = tokio::time::interval(Duration::from_nanos(tick_ns));
         deps.actual_sample_rate
             .store(deps.config.sample_rate as u64, Ordering::SeqCst);
         loop {

src/goniometer.rs

@@ -58,6 +58,31 @@ mod tests {
         }
     }
 
+    #[test]
+    fn double_rate_transport_never_leaves_a_sixty_hz_display_interval_empty() {
+        let sample_rate = 48_000u32;
+        let period = 128usize;
+        let mut clock = GoniometerClock::default();
+        let mut processed = 0usize;
+        let mut previous_emission = None;
+        let mut largest_gap = 0usize;
+
+        while processed < sample_rate as usize * 10 {
+            processed += period;
+            if clock.advance(period, sample_rate, 120) {
+                if let Some(previous) = previous_emission {
+                    largest_gap = largest_gap.max(processed - previous);
+                }
+                previous_emission = Some(processed);
+            }
+        }
+
+        assert!(
+            largest_gap <= sample_rate as usize / 60,
+            "largest transport gap was {largest_gap} samples"
+        );
+    }
+
     #[test]
     fn selection_never_upsamples_and_keeps_endpoints() {
         assert_eq!(selected_sample_indices(3, 1024), vec![0, 1, 2]);