サイン波の重ね合わせ

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import os
import numpy as np
import matplotlib.pyplot as plt
from functools import reduce
from scipy.io import wavfile

A = 0.2
fs = 44100
duration = 2

t = np.arange(0, fs * duration) / fs
num = int(os.environ.get('F0_NUM', '1'))
f0_list = np.arange(1, num + 1) * 261.63
y = reduce(lambda x, f0: x + A * np.sin(2 * np.pi * f0 * t), f0_list, np.zeros_like(t))

fade_ms = 20
fade_size = int(len(y) * fade_ms / (duration * 1000))
fade_filter = np.concatenate([np.linspace(0, 1, fade_size), np.ones(len(y) - fade_size * 2), np.linspace(1, 0, fade_size)])
faded = y * fade_filter

plt.plot(t * 1000, faded)

plt.xlabel('ms')
plt.ylabel('amplitude')

plt.xlim(0, 50)

if os.environ.get('SHOW_PLOT') == '1':
    plt.show()
else:
    plt.savefig(f'output/sine_overtone_{num}.png')

wavfile.write(f'output/sine_overtone_{num}.wav', fs, (faded * 32767).astype(np.int16))