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Sustain

# Take a sound and two numbers, representing the lengths of the attack
# phase of the sound, and the desired length of the sustain phase respectively.
# It returns a sustained sound.
# This function emulates a sustain effect on a guitar and works best with a 
# plucked/struck instrument with well-defined attack phase, short or
# non-existent sustain, and long decay.
def sustain(sound, attLength, susLength):
  length = getLength(sound)
  attLength = min(attLength, length) # Input error checking and correction

  # Create sustainSound, the sound "canvas"
  numSamples = length + susLength
  seconds = (numSamples / getSamplingRate(sound)) + 1
  sustainSound = makeEmptySound(int(seconds))

  #Copy attack phase
  for sampleNum in range(1, attLength):
    value = getSampleValueAt(sound, sampleNum)
    setSampleValueAt(sustainSound, sampleNum, value)

  #Copy sustain, starting immediately after the attack phase
  start = attLength+1
  repeatLength = 300 # Magic number, seems to work ok for the B4 note
  for sampleNum in range(start, start+susLength):
    value = getSampleValueAt(sound, start+(sampleNum%repeatLength))
    setSampleValueAt(sustainSound, sampleNum, value)

  #Copy rest of sound
  start = start + susLength
  for sampleNum in range(attLength+repeatLength+1, getLength(sound)+1):
    value = getSampleValueAt(sound, sampleNum)
    setSampleValueAt(sustainSound, sampleNum + start, value) 

  return sustainSound

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• Slides and Code- Spring 2008 last edited on 23 April 2008 at 11:00 am by lawn-128-61-23-153.lawn.gatech.edu