问理解快速傅立叶变换方法的输出

EN

import sqlite3
import struct
import numpy as np
from matplotlib import pyplot as plt
import time
import math

conn = sqlite3.connect(r"C:\my_test_data.sqlite")
c = conn.cursor()

c.execute('SELECT ID, time, data_blob FROM log_tbl')


for row in c:
    data_raw = bytes(row[2])
    data_raw_floats = struct.unpack('f'*1024, data_raw)
    data_np = np.asarray(data_raw_floats)

    data_normalized = (data_np - data_np.mean()) / (data_np.max() - data_np.min())

    fft = np.fft.fft(data_normalized)
    N = data_normalized .size

    plt.figure(1)
    plt.subplot(211)
    plt.plot(data_normalized )

    plt.subplot(212)
    plt.plot(np.abs(fft)[:N // 2] * 1 / N)
    plt.show()

    plt.clf()