DTMF.py

# DTMF.py: Dual Tone Multi-Frquency DTMF encoder and decoder
#	 By running this program, p2.wav is generated from 
#	 DTMF signal encoded from the user-input key
#	 
# 12/8/2003
# Jiwon Hahn

from wave import *
from math import *
from sys import *

PI2 = 6.283185306
scale = 32767 #16-bit unsigned short
FR = 44000 #framerate

keys=   '1','2','3','A',\
	'4','5','6','B',\
	'7','8','9','C',\
	'*','0','#','D'
F1 = [697,770,852,941]
F2 = [1209, 1336, 1477, 1633]


# Encoder takes a symbol X as input and generate a
# corresponding one second long DTMF tone, sampled at 
# 44,000 16-bit samples/sec, and store it in a wav file.

def encoder(symbol):
	for i in range(16):
		if symbol == keys[i]:
			f1 = F1[i/4] #row
			f2 = F2[i%4] #column
	data = range(FR)
	for i in range(FR):
		p = i*1.0/FR
		data[i]=int(scale+(sin(p*f1*PI2)+sin(p*f2*PI2))/2*scale)
	store_wav(data)

# endian inversion for unsigned 8 bit	
def inv_endian(num):
	b=num2bit(num)
	N=len(b)
	sum = 0
	for i in range(N):
		sum += int(b.pop(0))*2**i
	return sum

def num2bit(num): #8bit
	b = []
	for i in range(7,-1,-1):
		if num>= 2**i:
			b.append('1')
			num-=2**i
		else:	b.append('0')
	return b
	
def store_wav(data):
	fout = open('p2.wav', 'w')
	#nchannel,sampwidth,framerate,nframes,comptype, compname
	fout.setparams((1,2,FR,FR,'NONE','not compressed'))	
	for i in range(FR):
		MS8bit = data[i]>>8
		LS8bit = data[i]-(MS8bit<<8)
	#	m,l= inv_endian(MS8bit),inv_endian(LS8bit)
	#	l,m= inv_endian(MS8bit),inv_endian(LS8bit)
	#	fout.writeframes(chr(l)+chr(m)) 
		fout.writeframes(chr(LS8bit)+chr(MS8bit))
	fout.close()

def read_wav():
	fin = open('p2.wav','r')
	n = fin.getnframes()
	d = fin.readframes(n)
	fin.close()
	
	data = []
	for i in range(n):
		#LS8bit = inv_endian(ord(d[2*i]))
		#MS8bit = inv_endian(ord(d[2*i+1]))
		LS8bit, MS8bit = ord(d[2*i]),ord(d[2*i+1])
		data.append((MS8bit<<8)+LS8bit)
	return data 


# Decoder takes a DTMF signal file (.wav), sampled at 44,000
# 16-bit samples per second, and decode the corresponding symbol X.

def decoder():
	data = read_wav()
	temp = []	
	for f1 in F1:
		for f2 in F2:
			diff = 0
			for i in range(FR): #assume phase has not shifted dramatically	
				p = i*1.0/FR
				S=int(scale+scale*(sin(p*f1*PI2)+sin(p*f2*PI2))/2)
				diff += abs(S-data[i])
			temp.append((diff,f1,f2))
	f1,f2 = min(temp)[1:] #retrieve the frequency of minimum signal distortion 
	i, j = F1.index(f1), F2.index(f2)	
	X = keys[4*i+j]
	print 'Decoded key is: ', X
	return X

	
def menu():
	while 1:
		print '**************************'
		print '1\t2\t3\tA'
		print '4\t5\t6\tB'
		print '7\t8\t9\tC'
		print '*\t0\t#\tD'
		print '**************************'
		X = raw_input('Enter a key, or x to exit: ') 
		if X not in keys: 
			if X is 'x': exit(0)
			print 'Invalid key...';
		else: return X


if __name__=='__main__':
	X = menu()
	encoder(X)
	x = decoder()