Merge pull request #6 from woodnx/skotsugi/chapter01

Skotsugi add chapter01

skotsugi/chapter01/q01.py

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+import numpy as np
+import matplotlib.pyplot as plt
+
+A = 1.0    # 振幅
+f0 = 440   # 周波数[Hz]
+sec = 3.0  # 信号の長さ[s]
+fs = 16000 # サンプリング周波数[Hz]
+PI = np.pi # 円周率
+
+n = np.arange(0, fs*sec) / fs  # 間隔（公差）を指定（start: 0, stop: sec, step: 1/sf）
+y = A * np.sin(2 * PI * f0 * n)
+
+plt.plot(n, y)
+
+plt.xlim(0, 1 / f0)
+plt.xlabel("time [sec]")
+plt.ylabel("Amplitude")
+
+plt.savefig("./skotsugi/chapter01/q1.png")

skotsugi/chapter01/q02.py

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+import numpy as np
+import soundfile as sf
+
+def make_sin_wave(A, f, fs, sec):
+  n = np.arange(0, fs*sec) / fs
+  return A * np.sin(2 * np.pi * f * n)
+
+if __name__ == "__main__":
+  fs = 16000 # サンプリング周波数[Hz]
+
+  y = make_sin_wave(1.0, 440, fs, 3.0)
+
+  sf.write("./skotsugi/chapter01/q02.wav", y, fs)

skotsugi/chapter01/q03.py

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+import numpy as np
+import soundfile as sf
+from q02 import make_sin_wave
+
+fs = 16000 # サンプリング周波数[Hz]
+sec = 3.0
+
+y = np.zeros((int(fs*sec), 2), dtype=float)  
+y[:,0] = make_sin_wave(1.0, 440, fs, sec)
+y[:,1] = make_sin_wave(1.0, 660, fs, sec)
+
+sf.write("./skotsugi/chapter01/q03.wav", y, fs)

skotsugi/chapter01/q04.py

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+import numpy as np
+import matplotlib.pyplot as plt
+
+def make_white_noise(length):
+  return np.random.normal(size=int(length))
+
+if __name__ == "__main__":
+  np.random.seed(0)
+
+  fs = 16000 # サンプリング周波数[Hz]
+  sec = 3.0
+
+  y = make_white_noise(fs*sec)
+  n = np.arange(0, 3.0, 1/fs)
+
+  plt.plot(n, y)
+
+  plt.xlim(0)
+  plt.xlabel("time [sec]")
+  plt.ylabel("Amplitude")
+
+  plt.savefig("./skotsugi/chapter01/q4.png")

skotsugi/chapter01/q05.py

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+import numpy as np
+import matplotlib.pyplot as plt
+from q02 import make_sin_wave
+from q04 import make_white_noise
+
+np.random.seed(0)
+
+fs = 16000 # サンプリング周波数[Hz]
+sec = 3.0
+
+y = make_white_noise(fs*sec) + make_sin_wave(1.0, 440, fs, 3.0)
+
+n = np.arange(0, 3.0, 1/fs)
+
+plt.plot(n, y)
+
+plt.xlim(0)
+plt.xlabel("time [sec]")
+plt.ylabel("Amplitude")
+
+plt.savefig("./skotsugi/chapter01/q5.png")

skotsugi/chapter01/q06.py

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+import math
+import numpy as np
+from q02 import make_sin_wave
+from q04 import make_white_noise
+
+def square_mean(x):
+  # return np.sum(x ** 2) # <- これだとうまくいかなかった
+  return np.mean(x ** 2)
+
+def sn_rate(s, x): 
+  if (len(s) != len(x)):
+    return
+
+  s_sum = square_mean(s)
+  x_sum = square_mean(x)
+
+  return 10 * math.log10(s_sum / x_sum)
+
+##### DEBUG #####
+if __name__ == "__main__":
+  np.random.seed(0)
+
+  fs = 16000
+  sec = 3.0
+
+  s = make_sin_wave(1.0, 440, fs, 3.0)
+  x = make_white_noise(fs*sec)
+
+  print(sn_rate(s, x))

skotsugi/chapter01/q07.py

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+import numpy as np
+from q02 import make_sin_wave
+from q04 import make_white_noise
+from q06 import square_mean, sn_rate
+
+def add_noise_to_signal(signal, snr):
+  s_power = square_mean(signal)
+
+  snr_linear = 10.0 ** (snr / 10.0)
+  n_power = s_power / snr_linear
+
+  noise = np.sqrt(n_power) * make_white_noise(len(signal))
+  noisy_signal = signal + noise
+
+  return noisy_signal, noise
+
+##### DEBUG #####
+if __name__ == "__main__":
+  np.random.seed(0)
+
+  fs = 16000
+  sec = 3.0
+
+  signal = make_sin_wave(1.0, 440, fs, sec)
+  noisy_signal, noise = add_noise_to_signal(signal, 20)
+
+  print(sn_rate(signal, noise))

skotsugi/chapter01/q08.py

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+import numpy as np
+import soundfile as sf
+from q02 import make_sin_wave
+from q07 import add_noise_to_signal
+
+np.random.seed(0)
+
+fs = 16000
+sec = 3.0
+
+signal = make_sin_wave(1.0, 440, fs, sec)
+noisy_signal, noise = add_noise_to_signal(signal, 6)
+
+sf.write("./skotsugi/chapter01/q08.wav", noisy_signal, fs)

skotsugi/chapter01/q09.py

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+import soundfile as sf
+
+signal, fs = sf.read('./skotsugi/chapter01/q08.wav')
+
+down_scaled = signal[0:-1:2]
+
+sf.write("./skotsugi/chapter01/q09.wav", down_scaled, 8000)

skotsugi/chapter01/q10.py

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+import numpy as np
+
+def dma(x, k):
+  y = np.zeros(len(x))
+  for i in range(len(x) - k):
+    y[i] = np.mean(x[i:i+k])
+  return y
+
+if __name__ == "__main__":
+  import soundfile as sf
+  signal, fs = sf.read('./skotsugi/chapter01/q09.wav')
+
+  dmaed = dma(signal, 5)
+
+  sf.write("./skotsugi/chapter01/q10.wav", dmaed, 8000)