library("audio")
 
# gen_sin(): generate sine signal
#
# sample rate=44100 Hz
# f:    frquency in Hz
# ms:   duration in milliseconds
gen_sin<-function(f, ms)
{
  x<-NULL
  k=44100/(2*pi*f)
  x<-sin(0:(44100*(ms/1000))/k)
  return(x)
}
 
# Check
gen_sin(440,10)
 
# envelope(): generate simple linear AD envelope
#
# x:            signal returned by gen_sin
# attack_ms:    attack time in milliseconds
# decay:        decay time in milliseconds
# max_vol:      maximum volume should not exceed 1 
#               to avoid clipping
envelope<-function(x, attack_ms, decay_ms, max_vol)
{
  length=length(x)
 
  attack_start=1
  attack_end=44100*(attack_ms/1000)
  attack_slope=max_vol/(attack_end-attack_start)
 
  decay_end=length(x)
  decay_start=decay_end-44100*(decay_ms/1000)
  decay_slope=max_vol/(decay_end-decay_start)
 
  env<-rep(max_vol, length)
 
  volume_attack=0
  for(i in attack_start:attack_end)
  { 
    env[i]=volume_attack
    volume_attack=volume_attack+attack_slope
  }
  volume_decay=max_vol
  for(i in (decay_start):decay_end)
  {
    env[i]=volume_decay
    volume_decay=volume_decay-decay_slope
  }
  return(env)  
}
 
# Checks
x<-gen_sin(440,100)
length(x)
plot(x)
env<-envelope(x,50,50,0.5)
length(env)
plot(env)
 
# gen note(): generate note
#
# f:          frequency in Hertz
# ms:         duration in milliseconds
# attack_ms:    attack time in milliseconds
# decay:        decay time in milliseconds
# max_vol:      maximum volume should not exceed 1 
#               to avoid clipping
gen_note<-function(f, ms, attack_ms, decay_ms, max_vol)
{
  x<-gen_sin(f,ms)
  env<-envelope(x,attack_ms, decay_ms, max_vol)
  env_signal<-x*env
  return(env_signal)
}
 
x<-gen_note(440,1000,100,500,1)
play(x)
plot(x)
 
# gen_triad(): generate frequencies of a triad
# note:        base note of triad
# freq_scale:  scale frequencies
gen_triad<-function(note, freq_scale)
{
  chord<-NULL
  for(i in 1:3)
  {
    index=((note-1)%%16)+1 # R starts counting with 1
    note=note+2
    chord<-c(chord, gen_note(freq_scale[index], 400,40,200,0.8))
  }
    return(chord)
}
 
# Frequencies of the C major scale
freq_scale<-c(261.63, 293.66,  # C4 D4 
              329.63, 349.23,  # E4 F4
              392.00, 440.00,  # G4 A4
              493.88, 523.25,  # B4 C5
              587.33, 659.25,  # D5 E5
              698.46, 783.99)  # F5 G5  
 
# Check
plot(freq_scale)
# Play C Major chord
x<-gen_triad(1, freq_scale)
play(x)
 
### Generate piece ###
# Source of the alogrithm:
# Spiegel, L. (1982). Sonic Set Theory: A Tonal Music Theory for Computers. 
# In Proceedings of the Second Annual Symposium on Small Computers and the Arts.
#     
stages<-matrix(c(0, 0, 1, 0, 0, 0, 0,
                 0.5, 0, 0, 0, 0, 0.5, 0,
                 0, 0.5, 0, 0.5, 0, 0, 0,
                 0, 0, 0, 0, 0.5, 0, 0.5,
                 0.5, 0, 0, 0, 0, 0.5, 0), byrow=TRUE, ncol=7)
 
# Base notes of chords
base_notes<-rep(1:7) 
 
piece<-NULL
cycles=0
start=1
max_cycles=4
 
while(cycles<max_cycles)
{
  for(i in start:5)
  {
    index<-sample(base_notes,1, p=stages[i,])    
    piece<-c(piece, gen_triad(index, freq_scale))
    cat(index)
  }
  start=sample(2:5,1)
  cycles=cycles+1
}
 
play(piece)