[英]Calculate energy for each frequency band around frequency F of interest in Python
我是信號處理的新手,在這個問題中,我想問一下如何為感興趣的頻率F周圍的每個頻段獲取能量。我找到了一個公式,但我不知道如何在Python中實現它。 這是公式和我的傅里葉變換圖:
x = np.linspace(0,5,100)
y = np.sin(2*np.pi*x)
## fourier transform
f = np.fft.fft(y)
## sample frequencies
freq = np.fft.fftfreq(len(y), d=x[1]-x[0])
plt.plot(freq, abs(f)**2) ## will show a peak at a frequency of 1 as it should.
你幾乎就像麥克指出的那樣,但是這里有一個不同的方法,它更容易理解。你可以設置一個變量來保存濾波后的信號並返回一個Af的1d數組,然后應用上面的公式很簡單(平方和這些幅度)
過濾掉這樣的信號
from scipy.signal import butter, lfilter
def butter_bandpass(lowcut, highcut, fs, order=5):
nyq = 0.5 * fs
low = lowcut / nyq
high = highcut / nyq
b, a = butter(order, [low, high], btype='band')
return b, a
def butter_bandpass_filter(data, lowcut, highcut, fs, order=5):
b, a = butter_bandpass(lowcut, highcut, fs, order=order)
y = lfilter(b, a, data)
return y
現在假設y
是你的原始信號,你需要信號中5Hz分量的能量,
#let fs = 250
#let order = 5
oneD_array_of_amps_of_fiveHz_component = butter_bandpass_filter(y, 4, 6, 250, 5)
#calculate energy like this
energy_of_fiveHz_comp = sum([x*2 for x in oneD_array_of_amps_of_fiveHz_component])
使用在1D numpy數組中使用Numpy查找局部最大值/最小值的信號處理模塊,您將執行以下操作:
from scipy.signal import argrelextrema
import numpy as np
delta = 0.1
F = 1
X_delta = abs(freq - F) < delta
A_f_delta = abs(f[X_delta])**2
maximum_ix = argrelextrema(A_f, np.greater)
E_F_delta = np.sum(A_f[maximum_ix])/2
E_F_delta
2453.8235776144866
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