Frequency modulation

fm_bang.js

var pi = Math.PI;
var tau = Math.PI*2;
 
function arp(ts, x, y, z) {
  return Math.sin(x * Math.exp(-ts * y)) * Math.exp(-ts * z);
}
 
var sin = Math.sin;
var cos = Math.cos;
 
function tri(x) {
  return Math.abs(1 - (x % tau) / pi) * 2.0 - 1.0;
}
 
function saw(x) {
  return 1 - (x % tau) / pi;
}
 
function sqr(x) {
  return cos(x) > 0 ? 1 : -1;
}

function upol(x) {
  return x*0.5 + 0.5;
}
function bipol(x) {
  return x*2 - 1;
}

function clamp(x, mi, ma) {
  return Math.max(mi, Math.min(ma, x));
}
 
var c0 = 7, c1 = 2, c2 = sqr;
function dsp(t) {
  var dt = 1 / sampleRate;
  var ts = t % 3.0;
  if (ts - dt <= 0) {
    c0 = Math.random() * 2       + 7;
    c1 = Math.random() * 5 - 2.5 + 2;
    if (c1 < 0) c1 = 1 / -c1;
    c2 = [tri, saw, sqr, cos][Math.floor(Math.random()*4)];
  }
  var s = 301.467;
  var i = upol(tri(t*tau*c1))*c0;
  var b = t*tau*s / 7;
  var a = t*tau*s;
  return 0.5 * arp(ts, c2(a + i*cos(b)), tau/4, 0.1);
}