Karplus-Strong

karplus.js

/*
  Sort of string instrument simulation. I'm not sure where it's going to.
  http://boxbase.org/sequencer/
*/
var hpi = Math.PI/2;
var pi  = Math.PI;
var tau = Math.PI*2;
var sin = Math.sin;
var cos = Math.cos;

function dsp(t) {
    var sum = 0;
    for(var i = 0; i < midi.length; i++) {
        var vo = midi[i];
        var freq = vo.freq;
        var vel  = vo.vel;
        var y = 0.99;
        var l = Math.floor(sampleRate/vo.freq);
        var cut = 8000;
        if (!vo.ready) {
            vo.ready = true;
            vo.sync = Sync();
            vo.ring = new RingBuffer(l);
            vo.filt = new LowPass();
            
            for (var j = 0; j < l; j++) {
                var a = j / sampleRate;
                var k = noise();
                var q = vo.ring.last;
                k = vo.filt(q*y, cut) + k;
                vo.ring.push(k);
            }
        }
//        var x = /*sin(t*tau*freq)noise()*/ * clamp(1 + vo.t - t, 0.5, 1);
//        var x = sqr(t*tau*freq) * clamp(1 + vo.t - t, 0.5, 1);
        var x = sin(t*tau*freq) * 0.0;
        //var y = vo.ring.reduce(average, x);
        var z = vo.ring.last;
        
        x = vo.filt(z*y, cut) + x;
        //x = vo.filt(x + y, freq/2);
        //x = x + y*(0.5 + 0.4*saw(t*tau*freq));
        vo.ring.push(x);
        
        sum += x;
        //sum += vo.sync(tri(t*tau*freq*(2.0 + 1.95*tri(t*tau/100)) ), sqr(t*tau*freq));
        //sum += tri(freq*t*tau) * sqr((freq/4)*t*tau);
        /*
        if (midi[i].key < 70)
        {
            sum += sqr((freq/8+0.001*usin(freq/8*10.0*t*tau))*t*tau) * 0.5 * vel * Math.exp(z);
        } else if (midi[i].key > 80)
        {
            sum += clamp(tri(freq*t*tau), -0.5, 0.5)*0.1;
        } else
        {
            sum += sqr(freq*t*tau + tri(freq*t*tau/100)) * 0.1;
        }
        */
    }
    return sum / 6;
}

function average(n, x) {
    return (n+x) / 2;
}

function upol(x) {
    return x * 0.5 + 0.5;
}

function bpol(x) {
    return x * 2 - 1;
}

function usin(t) {
    return sin(t) * 0.5 + 0.5;
}
    
function tri(x) {
  return Math.abs(1 - ((x-hpi) % tau) / pi) * 2.0 - 1.0;
}
 
function saw(x) {
  return 1 - ((x-hpi) % tau) / pi;
}
 
function sqr(x) {
  return sin(x) > 0 ? 1 : -1;
}

function arp(ts, x, y, z) {
  return Math.sin(x * Math.exp(-ts * y)) * Math.exp(-ts * z);
}

function clamp(x, mi, ma) {
  return Math.max(mi, Math.min(ma, x));
}

function noise() {
    return Math.random() * 2 - 1;
}

/*
    linear interpolation between samples
 */
function mix(a, b, t) {
  t = clamp(t, 0.0, 1.0);
  var u = 1 - t;
  return a*u + b*t;
}

function LP() {
  var dout=0, din=0;
  return function (x, cutoff) {
    var rc = 1.0/(cutoff*2*tau);
    var dt = 1.0/sampleRate;
    var alpha = dt/(rc+dt);
    dout = dout + alpha*(x - dout);
    din  = x;
    return dout;
  };
}
 
function HP() {
  var dout=0, din=0;
  return function (x, cutoff) {
    var rc = 1.0/(cutoff*2*tau);
    var dt = 1.0/sampleRate;
    var alpha = rc/(rc+dt);
    dout = alpha*(dout + x - din);
    din  = x;
    return dout;
  };
}
 
/*
    supposed to reset the phase with an another signal
 */
function Sync() {
  var previous = 0;
  var start = 0;
  return function(signal, t) {
    if ((previous < 0) && (signal >= 0)) {
      start = t;
    }
    previous = signal;
    return t - start;
  };
}
 
/*
    butterworth filters, copied from http://basicsynth.com
 */
var sqr2 = 1.414213562;
 
function LowPass() {
  var dlyOut2 = 0, dlyOut1 = 0;
  var dlyIn2  = 0, dlyIn1  = 0;
  return function (x, cutoff_freq) {
    var c  = 1.0 / Math.tan((Math.PI / sampleRate) * cutoff_freq);
    var c2 = c*c;
    var csqr2 = sqr2 * c;
    var d = c2 + csqr2 + 1;
    var In0 = 1 / d;
    var In1 = In0 + In0;
    var In2 = In0;
    var Out1 = (2 * (1 - c2)) / d;
    var Out2 = (c2 - csqr2 + 1) / d;
    
    var out = (In0 * x)
            + (In1 * dlyIn1)
            + (In2 * dlyIn2)
            - (Out1 * dlyOut1)
            - (Out2 * dlyOut2);
    dlyOut2 = dlyOut1; dlyOut1 = out;
    dlyIn2  = dlyIn1;  dlyIn1  = x;
    return out;
  };
}
 
function HighPass() {
  var dlyOut2 = 0, dlyOut1 = 0;
  var dlyIn2  = 0, dlyIn1  = 0;
  return function (x, cutoff_freq) {
    var c  = Math.tan((Math.PI / sampleRate) * cutoff_freq);
    var c2 = c*c;
    var csqr2 = sqr2 * c;
    var d = c2 + csqr2 + 1;
    var In0 = 1 / d;
    var In1 = -(In0 + In0);
    var In2 = In0;
    var Out1 = (2 * (c2 - 1)) / d;
    var Out2 = (1 - csqr2 + c2) / d;
    
    var out = (In0 * x)
            + (In1 * dlyIn1)
            + (In2 * dlyIn2)
            - (Out1 * dlyOut1)
            - (Out2 * dlyOut2);
    dlyOut2 = dlyOut1; dlyOut1 = out;
    dlyIn2  = dlyIn1;  dlyIn1  = x;
    return out;
  };
}
 
function BandPass() {
  var dlyOut2 = 0, dlyOut1 = 0;
  var dlyIn2  = 0, dlyIn1  = 0;
  return function (x, cutoff_freq) {
    var c = 1 / Math.tan((Math.PI / sampleRate) * cutoff_freq);
    var d = 1 + c;
    var In0 = 1 / d;
    var In1 = 0;
    var In2 = -In0;
    var Out1 = (-c*2*Math.cos(2*Math.PI*cutoff_freq/sampleRate)) / d;
    var Out2 = (c - 1) / d;
    
    var out = (In0 * x)
            + (In1 * dlyIn1)
            + (In2 * dlyIn2)
            - (Out1 * dlyOut1)
            - (Out2 * dlyOut2);
    dlyOut2 = dlyOut1; dlyOut1 = out;
    dlyIn2  = dlyIn1;  dlyIn1  = x;
    return out;
  };
}
 
function RingBuffer(length){
  this.array = new Float32Array(length);
  this.length = length;
  this.pos = 0;
  this.last  = 0;
  this.first = 0;
}

RingBuffer.prototype.push = function(el){
  this.last  = this.array[this.pos];
  this.first = el;
  this.array[this.pos++] = el;
  if (this.pos === this.length) {
    this.pos = 0;
  }
};

RingBuffer.prototype.forEach = function(fn){
  var i = this.pos;
  for (; i < this.length; i++) {
    fn(this.array[i]);
  }
  if (this.pos > 0) {
    for (i = 0; i < this.pos; i++) {
      fn(this.array[i]);
    }
  }
};

RingBuffer.prototype.reduce = function(fn, val){
  val = val || 0;
  this.forEach(function(el){
    val = fn(val, el);
  });
  return val;
};