genish.js
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JavaScript
/**********************************************
****** Comb Filter (filtered-feedback) ********
***********************************************
A comb filter plays sums an input signal with a delayed version of
itself, creating 'notches' in the resulting frequency response. A common
DSP technique is to introduce a lowpass filtering stage into the feedback
loop for feedback dampening, which is what this demo implements.
The Filtered-Feedback Comb Filter has many applications in both artificial
reverberation and physical modeling. For more information see:
https://ccrma.stanford.edu/~jos/pasp/Filtered_Feedback_Comb_Filters.html
*/
// for each example, load the amen break first and then create our
// graph. We need to know the length of the file before we cna set
// all our parameters
data( './resources/audiofiles/amen.wav' ).then( amenData => {
// comb filter parameters
combLength = 1200
feedbackCoeff = param( 'feedback', .84 )
damping = param( 'damping', .2 )
// read samples from our data buffer
amenSignal = peek( amenData, accum( 1,0,{max:amenData.buffer.length} ), { interp:'none', mode:'samples' } )
// where in our delayed signal we will read / write to
readWriteIdx = counter( 1,0,combLength )
// create our delay buffer
combBuffer = data( combLength )
// store the last sample for our lowpass filtering
lastSample = ssd()
// read from the delay buffer; this is our final output signal
out = peek( combBuffer, readWriteIdx, { interp:'none', mode:'samples' })
// for our lowpass flitering, combine the current sample and the last sample, with damping
storeInput = add( mul( out, sub( 1, damping)), mul( lastSample.out, damping ) )
lastSample.in( storeInput )
// write sum of input signal and feedback signal to delay buffer
poke( combBuffer, add( amenSignal, mul( storeInput, feedbackCoeff ) ), readWriteIdx )
play( out ).then( node => {
gui = new dat.GUI()
gui.add( node, 'damping', 0,.995 )
gui.add( node, 'feedback', 0,.995 )
})
})