gibberish-dsp/js/filters/svf.js

Gibberish is designed to be an optimized API for audio synthesis using per-sample techniques.

const g = require( 'genish.js' ),
      filter = require( './filter.js' )

module.exports = function( Gibberish ) {
  Gibberish.genish.svf = ( input, cutoff, Q, mode, isStereo=false, shouldConvertFreqQ=false ) => {
    let d1 = g.data([0,0], 1, { meta:true }), d2 = g.data([0,0], 1, { meta:true }),
        peekProps = { mode:'simple', interp:'none' }

    if( shouldConvertFreqQ === true ) {
      //Q = g.min( g.add(.01 , __Q), 1 ) 
      cutoff = g.mul( g.max( .005, g.min( cutoff,.995 ) ), g.div( g.gen.samplerate, 4 ) )
    }

    let f1 = g.memo( g.mul( 2 * Math.PI, g.div( cutoff, g.gen.samplerate ) ) )
    let oneOverQ = g.memo( g.div( 1, Q ) )
    let l = g.memo( g.add( d2[0], g.mul( f1, d1[0] ) ) ),
        h = g.memo( g.sub( g.sub( isStereo ? input[0] : input, l ), g.mul( Q, d1[0] ) ) ),
        b = g.memo( g.add( g.mul( f1, h ), d1[0] ) ),
        n = g.memo( g.add( h, l ) )

    d1[0] = b
    d2[0] = l

    let out = g.selector( mode, l, h, b, n )

    let returnValue
    if( isStereo ) {
      let d12 = g.data([0,0], 1, { meta:true }), d22 = g.data([0,0], 1, { meta:true })
      let l2 = g.memo( g.add( d22[0], g.mul( f1, d12[0] ) ) ),
          h2 = g.memo( g.sub( g.sub( input[1], l2 ), g.mul( Q, d12[0] ) ) ),
          b2 = g.memo( g.add( g.mul( f1, h2 ), d12[0] ) ),
          n2 = g.memo( g.add( h2, l2 ) )

      d12[0] = b2
      d22[0] = l2

      let out2 = g.selector( mode, l2, h2, b2, n2 )

      returnValue = [ out, out2 ]
    }else{
      returnValue = out
    }

    return returnValue
  }

  let SVF = inputProps => {
    const svf = Object.create( filter )
    const props = Object.assign( {}, SVF.defaults, filter.defaults, inputProps ) 

    const isStereo = props.input.isStereo
    
    // XXX NEEDS REFACTORING
    const __out = Gibberish.factory( 
      svf,
      //Gibberish.genish.svf( g.in('input'), g.mul( g.in('cutoff'), g.gen.samplerate / 5 ), g.sub( 1, g.in('Q') ), g.in('mode'), isStereo ), 
      Gibberish.genish.svf( g.in('input'), g.mul( g.in('cutoff'), g.gen.samplerate / 5 ), g.sub( 1, g.in('Q') ), g.in('mode'), isStereo, true ), 
      ['filters','Filter12SVF'], 
      props
    )

    return __out
  }


  SVF.defaults = {
    input:0,
    Q: .65,
    cutoff:.25,
    mode:0
  }

  return SVF

}