music - string.go

     1  package music
     2  
     3  import "math/rand"
     4  
     5  // https://uk.mathworks.com/help/signal/examples/generating-guitar-chords-using-the-karplus-strong-algorithm.html
     6  // http://www.cs.princeton.edu/courses/archive/fall07/cos126/assignments/guitar.html
     7  
     8  type String struct {
     9  	data  []float64
    10  	pos   int
    11  	decay float64
    12  }
    13  
    14  const StringDecay = 0.4998
    15  
    16  func NewString(n Note, rate, decay float64) *String {
    17  	return &String{
    18  		data:  make([]float64, int(rate/float64(n))),
    19  		decay: decay,
    20  	}
    21  }
    22  
    23  func (s *String) Pluck() {
    24  	for i := range s.data {
    25  		s.data[i] = rand.Float64()*2 - 1
    26  	}
    27  	s.pos = 0
    28  }
    29  
    30  func (s *String) Next(_ float64) float64 {
    31  	p := s.pos
    32  	f := s.data[p]
    33  	s.pos++
    34  	if s.pos == len(s.data) {
    35  		s.pos = 0
    36  	}
    37  	s.data[p] = s.decay * (f + s.data[s.pos])
    38  	return f
    39  }