Clip a Sound

# returns a new sound that is the portion of "source" from "start" to "end"
# doesn't alter the original sound.
def clip (source, start, end):
  target = makeEmptySound (end - start, 44100)
  targetIndex = 0
  for sourceIndex in range (start, end):
    sourceValue = getSampleValueAt (source, sourceIndex)
    setSampleValueAt (target, targetIndex, sourceValue)
    targetIndex = targetIndex + 1
  return target