gibberish-dsp/js/fx/freeverb.js

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

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

module.exports = function( Gibberish ) {
  
const allPass = Gibberish.filters.genish.AllPass
const combFilter = Gibberish.filters.genish.Comb

const tuning = {
  combCount:	  	8,
  combTuning: 		[ 1116, 1188, 1277, 1356, 1422, 1491, 1557, 1617 ],                    
  allPassCount: 	4,
  allPassTuning:	[ 225, 556, 441, 341 ],
  allPassFeedback:0.5,
  fixedGain: 		  0.015,
  scaleDamping: 	0.4,
  scaleRoom: 		  0.28,
  offsetRoom: 	  0.7,
  stereoSpread:   23
}

const Freeverb = inputProps => {
  const props = Object.assign( {}, effect.defaults, Freeverb.defaults, inputProps ),
        reverb = Object.create( effect ) 

  let out 
  reverb.__createGraph = function() {
    let isStereo = false
    if( out === undefined ) {
      isStereo = typeof props.input.isStereo !== 'undefined' ? props.input.isStereo : false 
    }else{
      isStereo = out.input.isStereo
    }    

    const combsL = [], combsR = []

    const input = g.in( 'input' ),
          inputGain = g.in( 'inputGain' ),
          wet1 = g.in( 'wet1'),
          wet2 = g.in( 'wet2' ),  
          dry = g.in( 'dry' ), 
          roomSize = g.in( 'roomSize' ), 
          damping = g.in( 'damping' )
    
    const __summedInput = isStereo === true ? g.add( input[0], input[1] ) : input,
          summedInput = g.mul( __summedInput, inputGain ),
          attenuatedInput = g.memo( g.mul( summedInput, tuning.fixedGain ) )
    
    // create comb filters in parallel...
    for( let i = 0; i < 8; i++ ) { 
      combsL.push( 
        combFilter( 
          attenuatedInput, 
          tuning.combTuning[i], 
          g.mul(damping,.4),
          g.mul( tuning.scaleRoom + tuning.offsetRoom, roomSize ) 
        ) 
      )
      combsR.push( 
        combFilter( 
          attenuatedInput, 
          tuning.combTuning[i] + tuning.stereoSpread, 
          g.mul(damping,.4), 
          g.mul( tuning.scaleRoom + tuning.offsetRoom, roomSize ) 
        ) 
      )
    }
    
    // ... and sum them with attenuated input, use of let is deliberate here
    let outL = g.add( attenuatedInput, ...combsL )
    let outR = g.add( attenuatedInput, ...combsR )
    
    // run through allpass filters in series
    for( let i = 0; i < 4; i++ ) { 
      outL = allPass( outL, tuning.allPassTuning[ i ] + tuning.stereoSpread )
      outR = allPass( outR, tuning.allPassTuning[ i ] + tuning.stereoSpread )
    }
    
    const outputL = g.add( g.mul( outL, wet1 ), g.mul( outR, wet2 ), g.mul( isStereo === true ? input[0] : input, dry ) ),
          outputR = g.add( g.mul( outR, wet1 ), g.mul( outL, wet2 ), g.mul( isStereo === true ? input[1] : input, dry ) )

    reverb.graph = [ outputL, outputR ]
  }

  reverb.__createGraph()
  reverb.__requiresRecompilation = [ 'input' ]

  out = Gibberish.factory( reverb, reverb.graph, ['fx','freeverb'], props )

  return out
}


Freeverb.defaults = {
  input: 0,
  wet1: 1,
  wet2: 0,
  dry: .5,
  roomSize: .925,
  damping:  .5,
}

return Freeverb 

}