簡單的濾波

fft_filter.py

import numpy as np
import matplotlib.pyplot as plt

t = 2              # 取樣時間
sample_rate = 800  # 取樣率，每秒取幾個樣本

def signal(t, sample_rate):
    f = 10
    x = np.linspace(0, t, int(t * sample_rate), endpoint = False)
    return (np.sin(f * 2 * np.pi * x) +    
            np.sin(3 * f * 2 * np.pi * x) / 2 + 
            np.sin(4 * f * 2 * np.pi * x) / 5 +
            np.sin(8 * f * 2 * np.pi * x) / 3)

samples = signal(t, sample_rate)
sp = np.fft.fft(samples) 
freq = np.fft.fftfreq(samples.size, d = 1 / sample_rate)

sp2 = sp.copy()
# 頻率 10 與 -10 以外的部份設為 0
sp2[np.intersect1d(np.where(freq != 10), np.where(freq != -10))] = 0
# 逆轉換
samples2 = np.fft.ifft(sp2).real

x = np.linspace(0, t, int(t * sample_rate), endpoint = False)
plt.plot(x, samples)
plt.plot(x, samples2)
plt.show()