SPL Meter 0.4.0: a dead input must not look like a quiet room

AB's meter appeared to halt for a day and a half. Nothing had halted: the
capture child had run continuously since the machine was restarted, never
stalled, never exited, and was delivering twenty frames a second. Every one
of them was digital silence, because Dante Via stopped passing audio after
the reboot — the Timers module's LTC listener, on channel 16 of the same
device, had been reporting no signal for exactly as long.

The module's part in that was reporting "ok" through all of it and drawing
a steady -83, which is the -200 floor plus the +117 calibration offset. A
plausible number on a wall is believed, and a green dot beside it says the
number is worth believing. That is worse than showing nothing.

So silence is now a state the module names. Below -150 dBFS unweighted the
input is not quiet, it is absent: a microphone in a silent room still reads
about -83, and even a muted converter dithers. Five seconds of that on every
channel and health() goes to error naming the device and how long it has
been dead, the tiles stop drawing a level and say "No audio" with how long,
and the status dot goes red.

Verified both directions, which is the half that matters: BlackHole with
nothing routed into it is caught in five seconds, and a real microphone in a
quiet room at -49 dBFS is never flagged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

modules/spl-meter/client.js

@@ -17,6 +17,21 @@
 
 const FLOOR = -200;
 
+/**
+ * A dead input reads as a number, and a number on a wall is believed. Every
+ * tile therefore refuses to draw a level while the server says the input is
+ * digitally silent, and says why instead.
+ */
+function silentFor(payload) {
+  return payload && payload.silentSec ? payload.silentSec : 0;
+}
+
+function silentText(sec) {
+  if (sec < 90) return `No audio — ${sec} s`;
+  const m = Math.round(sec / 60);
+  return m < 90 ? `No audio — ${m} min` : `No audio — ${(m / 60).toFixed(1)} hours`;
+}
+
 /** Retention per frame for the RTA's smoothing setting. */
 const SMOOTHING = { off: 0, light: 0.45, medium: 0.72, heavy: 0.9 };
 
@@ -37,6 +52,9 @@ export default function create({ root, moduleApi }) {
       moduleApi.setStatus('error', payload.error);
     } else if (!payload.frame) {
       moduleApi.setStatus('connecting', 'waiting for the first reading');
+    } else if (silentFor(payload)) {
+      moduleApi.setStatus('error',
+        `No audio on the chosen input — digital silence for ${silentText(silentFor(payload)).replace('No audio — ', '')}`);
     } else if (!payload.calibrated) {
       moduleApi.setStatus('ok', 'Measuring, but uncalibrated — these are dBFS, not dB SPL');
     } else {
@@ -233,6 +251,16 @@ function readoutView(root, moduleApi) {
     render(payload) {
       const s = moduleApi.instanceSettings;
       const ch = pickChannel(payload, s);
+      const quiet = silentFor(payload);
+      if (quiet && ch) {
+        num.textContent = '––.–';
+        unit.textContent = '';
+        sub.hidden = false;
+        sub.textContent = silentText(quiet);
+        box.dataset.level = 'dead';
+        fit();
+        return;
+      }
       if (!payload || payload.error || !ch) {
         num.textContent = '––.–';
         sub.textContent = payload && payload.error ? payload.error : '';
@@ -286,6 +314,7 @@ function barsView(root, moduleApi) {
           </div>`).join('');
       }
       const s = moduleApi.instanceSettings;
+      const quiet = silentFor(payload);
       const warn = Number(s.warnAt), alarm = Number(s.alarmAt);
       const showPeak = s.peakHold !== false;
       const lo = payload.calibrated ? 40 : -80;
@@ -295,12 +324,12 @@ function barsView(root, moduleApi) {
         if (!el) continue;
         const value = readValue(c, { averaging: s.averaging });
         const pct = (v) => Math.max(0, Math.min(100, ((v - lo) / (hi - lo)) * 100));
-        el.querySelector('.spl-bar-fill').style.width = `${pct(value)}%`;
+        el.querySelector('.spl-bar-fill').style.width = quiet ? '0%' : `${pct(value)}%`;
         const peak = el.querySelector('.spl-bar-peak');
         peak.style.display = showPeak ? '' : 'none';
         if (showPeak) peak.style.left = `${pct(c.peakC)}%`;
-        el.querySelector('.spl-bar-value').textContent = fmt(value);
-        el.dataset.level = !payload.calibrated ? 'idle'
+        el.querySelector('.spl-bar-value').textContent = quiet ? '––.–' : fmt(value);
+        el.dataset.level = quiet ? 'dead' : !payload.calibrated ? 'idle'
           : value >= alarm ? 'alarm' : value >= warn ? 'warn' : 'ok';
         el.classList.toggle('clip', !!c.clip);
       }
@@ -389,10 +418,12 @@ function spectrumView(root, moduleApi, scrolling) {
       const muted = themeColor(root, '--muted', '#888');
       const border = themeColor(root, '--border', '#333');
 
-      if (!payload || !payload.frame || !payload.frame.bands) {
+      const quiet = silentFor(payload);
+      if (quiet || !payload || !payload.frame || !payload.frame.bands) {
         ctx.fillStyle = bg; ctx.fillRect(0, 0, w, h);
         ctx.fillStyle = muted; ctx.font = '12px system-ui'; ctx.textAlign = 'center';
-        ctx.fillText(payload?.error || 'Spectrum analysis is off', w / 2, h / 2);
+        ctx.fillText(quiet ? silentText(quiet)
+                     : (payload?.error || 'Spectrum analysis is off'), w / 2, h / 2);
         painted = false;
         return;
       }