Animate mugshot party identification

src/audio.ts

@@ -21,6 +21,22 @@ function noise(context: AudioContext) {
   return noiseBuffer
 }
 
+let markerNoiseBuffer:AudioBuffer | null=null
+function markerNoise(context:AudioContext) {
+  if (!markerNoiseBuffer) {
+    const length=Math.floor(context.sampleRate * .31)
+    markerNoiseBuffer=context.createBuffer(1,length,context.sampleRate)
+    const data=markerNoiseBuffer.getChannelData(0)
+    let previous=0
+    for (let index=0;index < length;index++) {
+      const white=Math.random() * 2 - 1
+      previous=previous * .66 + white * .34
+      data[index]=previous * (.72 + Math.sin(index / 37) * .18)
+    }
+  }
+  return markerNoiseBuffer
+}
+
 const music = typeof Audio !== 'undefined' ? new Audio() : null
 if (music) music.loop = true
 let currentUrl: string | null = null
@@ -100,6 +116,28 @@ export const audio = {
     src.connect(filter).connect(gain).connect(context.destination)
     src.start(now); src.stop(now + 0.04)
   },
+  // A restrained felt-tip-on-paper scratch. The caller supplies the handwriting
+  // duration so the sound ends with the incremental letter reveal.
+  sharpie(durationMs:number) {
+    if (muted) return undefined
+    const context=audioContext()
+    if (!context) return undefined
+    if (context.state === 'suspended') void context.resume()
+    const duration=Math.max(.12,Math.min(3,durationMs / 1000))
+    const source=context.createBufferSource();source.buffer=markerNoise(context);source.loop=true
+    const filter=context.createBiquadFilter();filter.type='bandpass';filter.frequency.value=1180;filter.Q.value=.62
+    const gain=context.createGain()
+    const now=context.currentTime + .012,end=now + duration
+    gain.gain.setValueAtTime(.0001,now)
+    gain.gain.linearRampToValueAtTime(.032,now + .035)
+    for (let at=now + .055;at < end - .04;at += .045) gain.gain.setValueAtTime(.018 + Math.random() * .026,at)
+    gain.gain.exponentialRampToValueAtTime(.0001,end)
+    source.connect(filter).connect(gain).connect(context.destination)
+    let ended=false
+    source.onended=() => { ended=true }
+    source.start(now);source.stop(end + .02)
+    return () => { if (!ended) { try { source.stop() } catch { /* already stopped */ } } }
+  },
   // Resume the context and retry pending music on a user gesture.
   resume() {
     void audioContext()?.resume?.()