python3でAM復調

概要

python3で、AM復調やってみた。
AM信号は、5000Hzの搬送波、wavファイル。
復調アルゴリズムは、IQ復調。

AM信号

復調後の音声

サンプルコード

import numpy as np
import scipy.signal as sg
import wave
from scipy import fromstring, int16
from struct import pack

wavfile = "sHlM0.wav"
wr = wave.open(wavfile, "rb")
print (wr.getparams())
sample_rate = wr.getframerate()
para = wr.getparams()
wlen = wr.getnframes()
data = wr.readframes(wr.getnframes())
num_data = fromstring(data, dtype = int16)
left = num_data[::2]
right = num_data[1::2]
wr.close()
left = left
right = right
t = np.arange(wlen) / sample_rate
F_4KHz = 4000.
i1 = left * np.cos(t * 2 * np.pi * F_4KHz)
q1 = left * np.sin(t * 2 * np.pi * F_4KHz)
nyq_rate = sample_rate / 2.
cutoff_hz = 1000.0
lpf = sg.firwin(29, cutoff_hz / nyq_rate)
i2 = sg.lfilter(lpf, 1, i1)
q2 = sg.lfilter(lpf, 1, q1)
o = np.sqrt(i2 * i2 + q2 * q2) * 30
write_wave = wave.Wave_write("am7.wav")
write_wave.setparams(para)
for i in range(0, wlen):
    wvData = pack('h', int(o[i]))
    write_wave.writeframes(wvData)
    wvData = pack('h', int(o[i]))
    write_wave.writeframes(wvData)
write_wave.close()
print ("ok")