genish.js/playground/examples/biquad.dsp.js

gen~ in js

in1 = noise()

x1 = ssd(); x2 = ssd(); y1 = ssd(); y2 = ssd();
 
// define our coefficients
a0 = param( 'a0', .001453 ); a1 = param( 'a1', .002906 ); a2 = param( 'a2', .001453 )
b1 = param( 'b1', -1.888279 ); b2 = param( 'b2', .894091 );


/***** begin sample processing ******/
{
  'use jsdsp'

  in1a0 = x1.in( in1 ) * a0
  x1a1  = x2.in( x1.out ) * a1
  x2a2  = x2.out * a2
   
  sumLeft = in1a0 + x1a1 + x2a2
   
  y1b1 = y2.in( y1.out ) * b1
  y2b2 = y2.out * b2
   
  sumRight = y1b1 + y2b2
   
  diff = sumLeft - sumRight
   
  y1.in( diff )
   
  /****** end sample processsing ******/
   
  cb = play( diff, true )
}
 
// setup an object to store our filter parmaeters for use with a GUI
biquad = {
  frequency: 550,
  Q: .7,
  mode: 'LP'
}
 
// get coefficients and map them to the param() ugens we declared earlier
changeCoeffs = () => {
  [ cb.a0, cb.a1, cb.a2, cb.b1, cb.b2 ] = getCoeffs( biquad.frequency, biquad.Q, biquad.mode )
}
 
// create our GUI using dat.GUI
gui = new dat.GUI({ width:500 })
gui.add( biquad, 'frequency', 100, 10000 ).onChange( changeCoeffs )
gui.add( biquad, 'Q', 0, 20 ).onChange( changeCoeffs )
gui.add( biquad, 'mode', ['LP','BP','HP'] ).onChange( changeCoeffs )
 
// a function to generate coefficients based on cutoff, Q and filter mode
// no operator overloading (jsdsp) is used
getCoeffs = ( cutoff=330, Q=.7, mode='LP' ) => {
  let c,a1,a2,b0,b1,b2,w0,sinw0,cosw0,alpha
  c = a1 = a2 = b0 = b1 = b2 = 0
   
  switch ( mode ) {
    case 'LP':
     w0 = 2 * Math.PI * cutoff / gen.samplerate,
     sinw0 = Math.sin( w0 ),
     cosw0 = Math.cos( w0 ),
     alpha = sinw0 / (2 * Q);
 
     a0 = (1 - cosw0) / 2,
     a1 = 1 - cosw0,
     a2 = a0,
     c  = 1 + alpha,
     b1 = -2 * cosw0,
     b2 = 1 - alpha
 
     break;
    case "HP":
     w0 = 2 * Math.PI * cutoff / gen.samplerate,
     sinw0 = Math.sin( w0 ),
     cosw0 = Math.cos( w0 ),
     alpha = sinw0 / (2 * Q)
       
     a0 = (1 + cosw0) / 2,
     a1 = -(1 + cosw0),
     a2 = a0,
     c  = 1 + alpha,
     b1 = -2 * cosw0,
     b2 = 1 - alpha;
     break;
   case "BP":
     w0 = 2 * Math.PI * cutoff / gen.samplerate
     cosw0  = Math.cos( w0 ),
     sinw0  = Math.sin( w0 ),
     alpha  = sinw0 / ( 2 * Q )
     
     a0 = Q * alpha,
     a1 = 0,
     a2 = -Q * alpha,
     c  = 1 + alpha,
     b1 = -2 * cosw0,
     b2 = 1 - alpha
     break;
   default:
     break;
  }
 
  a0 = a0 / c;
  a1 = a1 / c;
  a2 = a2 / c;
  b1 = b1 / c;
  b2 = b2 / c;
  
  return [ a0, a1, a2, b1, b2 ]
}