analyze pitch

1 year ago · d2f38b67b6
parent f433d32cc0
commit d2f38b67b6
2 changed files with 88 additions and 0 deletions
--- a/analyze.js
+++ b/analyze.js
@ -0,0 +1,78 @@
+document.querySelector('#analyze-pitch button').addEventListener('click', startListening);
+
+function startListening() {
+    navigator.mediaDevices.getUserMedia({ audio: true, video: false })
+        .then(stream => {
+            const audioContext = new (window.AudioContext || window.webkitAudioContext)();
+            const analyser = audioContext.createAnalyser();
+            const microphone = audioContext.createMediaStreamSource(stream);
+            const scriptProcessor = audioContext.createScriptProcessor(2048, 1, 1);
+
+            analyser.smoothingTimeConstant = 0.3;
+            analyser.fftSize = 2048;
+
+            microphone.connect(analyser);
+            analyser.connect(scriptProcessor);
+            scriptProcessor.connect(audioContext.destination);
+
+            scriptProcessor.onaudioprocess = () => {
+                const buffer = new Float32Array(analyser.fftSize);
+                analyser.getFloatTimeDomainData(buffer);
+                const pitch = autoCorrelate(buffer, audioContext.sampleRate);
+                document.querySelector('#analyze-pitch dd').textContent = pitch.toFixed(2);
+            };
+        })
+        .catch(err => {
+            console.error('Error accessing microphone: ' + err);
+        });
+}
+
+function autoCorrelate(buffer, sampleRate) {
+    const SIZE = buffer.length;
+    const MAX_SAMPLES = Math.floor(SIZE / 2);
+    const MIN_SAMPLES = 0;
+    const GOOD_ENOUGH_CORRELATION = 0.9;
+
+    let bestOffset = -1;
+    let bestCorrelation = 0;
+    let rms = 0;
+    let foundGoodCorrelation = false;
+    let correlations = new Array(MAX_SAMPLES);
+
+    for (let i = 0; i < SIZE; i++) {
+        const val = buffer[i];
+        rms += val * val;
+    }
+    rms = Math.sqrt(rms / SIZE);
+
+    if (rms < 0.01) // not enough signal
+        return -1;
+
+    let lastCorrelation = 1;
+    for (let offset = MIN_SAMPLES; offset < MAX_SAMPLES; offset++) {
+        let correlation = 0;
+
+        for (let i = 0; i < MAX_SAMPLES; i++) {
+            correlation += Math.abs((buffer[i]) - (buffer[i + offset]));
+        }
+        correlation = 1 - (correlation / MAX_SAMPLES);
+        correlations[offset] = correlation;
+
+        if ((correlation > GOOD_ENOUGH_CORRELATION) && (correlation > lastCorrelation)) {
+            foundGoodCorrelation = true;
+            if (correlation > bestCorrelation) {
+                bestCorrelation = correlation;
+                bestOffset = offset;
+            }
+        } else if (foundGoodCorrelation) {
+            const shift = (correlations[bestOffset + 1] - correlations[bestOffset - 1]) / correlations[bestOffset];
+            return sampleRate / (bestOffset + (8 * shift));
+        }
+        lastCorrelation = correlation;
+    }
+    if (bestCorrelation > 0.01) {
+        return sampleRate / bestOffset;
+    }
+    return -1;
+}
+
--- a/index.html
+++ b/index.html
@ -5,10 +5,12 @@
 	<title></title>
 	<script src="http://unpkg.com/tone"></script>
 	<script src="app.js" defer></script>
+	<script src="analyze.js" defer></script>
 </head>
 <body>
 	<h1>Tuner</h1>
 	<section id="generate-tone">
+		<h2>Tone Generator</h2>
 		<dl>
 			<dt>Tone:</dt>
 			<dd></dd>
@ -17,5 +19,13 @@
 		<button>Play</button>
 		<button>Stop</button>
 	</section>
+	<section id="analyze-pitch">
+		<h2>Pitch Analyzer</h2>
+		<button>Analyze</button>
+		<dl>
+			<dt>Pitch:</dt>
+			<dd></dd>
+		</dl>
+	</section>
 </body>
 </html>