#!/usr/pkg/bin/python
"transpose WAV to another key by lengthening or shortening"

import sys, os, wave, struct, array
from winsound import *
format = {1: 'b', 2: 'h', 4: 'i'}
amount = 0 # amount to adjust pitch, in semitones

def transpose():
 global format, amount
 if sys.argv[1][0] == '-':
  sys.argv.pop(1)
  amount = sys.argv.pop(1)
  if int(amount) == 0:
   raise SyntaxError, 'transpose factor must be positive or negative integer'
 amount = int(amount)
 for filename in sys.argv[1:]:
  print filename
  infile = wave.open(filename, "rb")
  outfile = wave.open(filename + "%+d.wav" % amount, "wb")
  outfile.setparams(infile.getparams())
  (channels, samplewidth, framerate) = infile.getparams()[0:3]
  while True:
   chunk = infile.readframes(framerate)
   if len(chunk) == 0: break
   data = list(struct.unpack(format[samplewidth] * \
    (len(chunk) / samplewidth), chunk))
   data = array.array(format[samplewidth], data)
   data = modify(data, amount)
   outfile.writeframes(data.tostring())

def modify(data, amount):
 twelfth = 1.0 / 12
 length = len(data)
 # if the adjustment amount is negative (lower pitch) then obviously the
 # sample must be lengthened (more data played back at same speed), so we
 # negate the amount; then the exponent becomes positive
 newlength = int(length * pow(2, twelfth * -amount))
 ratio = float(length) / newlength
 data.append(data[-1]) # duplicate the last so we can average with sample + 1
 modified = array.array(data.typecode, [0] * newlength)
 try:
  for index in range(0, len(modified)):
   # if we're taking four samples and spreading them over 5, you have:
   # old[0]     | old[1]    | old[2]    | old[3]    |
   # new[0]  | new[1]  | new[2]  | new[3]  | new[4] |
   # new[0] will be the about the same as old[0], same with new[4] to old[3]
   # but new[2] will be somewhere between old[1] and old[2]
   # if old is [0, 1, 2, 3] then new is [0, .8, 1.6, 2.4, 3]
   # so the calculation is, in the case of new[1]:
   oldoffset = index * ratio # 4/5 * 1 = .8
   oldindex = int(oldoffset) # int(.8) = 0
   newvalue = data[oldindex] + \
    ((data[oldindex + 1] - data[oldindex]) * (oldoffset - oldindex))
   modified[index] = int(newvalue)
 except:
  raise
 return modified

if __name__ == "__main__":
 transpose()