audio-eq: flatten frequency response

2021-06-15 21:06:00 +02:00
parent cd52dea488
commit cf2d6650ac
4 changed files with 199 additions and 19 deletions
--- a/docs/biquad.html
+++ b/docs/biquad.html
@@ -0,0 +1,95 @@
+<!DOCTYPE html><html><head></head><body><script>
+
+setTimeout(location.reload.bind(location), 700);
+document.documentElement.scrollLeft = 0;
+
+var can = document.createElement('canvas'),
+    cc = can.getContext('2d'),
+    w = 2048,
+    h = 1024;
+
+w = 2048;
+
+can.width = w;
+can.height = h;
+document.body.appendChild(can);
+can.style.cssText = 'width:' + w + 'px;height:' + h + 'px';
+
+cc.fillStyle = '#000';
+cc.fillRect(0, 0, w, h);
+
+var cfg = [ // hz, q, g
+    [31.25 * 0.88, 0, 1.4],  // shelf
+    [31.25 * 1.04, 0.7, 0.96],  // peak
+    [62.5, 0.7, 1],
+    [125, 0.8, 1],
+    [250, 0.9, 1.03],
+    [500, 0.9, 1.1],
+    [1000, 0.9, 1.1],
+    [2000, 0.9, 1.105],
+    [4000, 0.88, 1.05],
+    [8000 * 1.006, 0.73, 1.24],
+    //[16000 * 1.00, 0.5, 1.75],  // peak.v1
+    //[16000 * 1.19, 0, 1.8]  // shelf.v1
+    [16000 * 0.89, 0.7, 1.26],  // peak
+    [16000 * 1.13, 0.82, 1.09],  // peak
+    [16000 * 1.205, 0, 1.9]  // shelf
+];
+
+var freqs = new Float32Array(22000),
+    sum = new Float32Array(freqs.length),
+    ac = new AudioContext(),
+    step = w / freqs.length,
+    colors = [
+        'rgba(255, 0, 0, 0.7)',
+        'rgba(0, 224, 0, 0.7)',
+        'rgba(0, 64, 255, 0.7)'
+    ];
+
+var order = [];
+
+for (var a = 0; a < cfg.length; a += 2)
+    order.push(a);
+
+for (var a = 1; a < cfg.length; a += 2)
+    order.push(a);
+
+for (var ia = 0; ia < order.length; ia++) {
+    var a = order[ia],
+        fi = ac.createBiquadFilter(),
+        mag = new Float32Array(freqs.length),
+        phase = new Float32Array(freqs.length);
+
+    for (var b = 0; b < freqs.length; b++)
+        freqs[b] = b;
+
+    fi.type = a == 0 ? 'lowshelf' : a == cfg.length - 1 ? 'highshelf' : 'peaking';
+    fi.frequency.value = cfg[a][0];
+    fi.Q.value = cfg[a][1];
+    fi.gain.value = 1;
+
+    fi.getFrequencyResponse(freqs, mag, phase);
+    cc.fillStyle = colors[a % colors.length];
+    for (var b = 0; b < sum.length; b++) {
+        mag[b] -= 1;
+        sum[b] += mag[b] * cfg[a][2];
+        var y = h - (mag[b] * h * 3);
+        cc.fillRect(b * step, y, step, h - y);
+        cc.fillRect(b * step - 1, y - 1, 3, 3);
+    }
+}
+
+var min = 999999, max = 0;
+for (var a = 0; a < sum.length; a++) {
+    min = Math.min(min, sum[a]);
+    max = Math.max(max, sum[a]);
+}
+cc.fillStyle = 'rgba(255,255,255,1)';
+for (var a = 0; a < sum.length; a++) {
+    var v = (sum[a] - min) / (max - min);
+    cc.fillRect(a * step, 0, step, v * h / 2);
+}
+
+cc.fillRect(0, 460, w, 1);
+
+</script></body></html>