title: How to remove frequency from signal
body: <p>I want to remove one frequency (one peak) from signal and plot my function without it. After fft I found frequency and amplitude and I am not sure what I need to do now. For example I want to remove my highest peak (marked with red dot on plot).</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  
  # create data
  N = 4097
  T = 100.0
  t = np.linspace(-T/2,T/2,N)
  f = np.sin(50.0 * 2.0*np.pi*t) + 0.5*np.sin(80.0 * 2.0*np.pi*t)
  
  #plot function
  plt.plot(t,f,'r')
  plt.show()
  
  # perform FT and multiply by dt
  dt = t[1]-t[0]
  ft = np.fft.fft(f) * dt      
  freq = np.fft.fftfreq(N, dt)
  freq = freq[:N/2+1]
  amplitude = np.abs(ft[:N/2+1])
  # plot results
  plt.plot(freq, amplitude,'o-')
  plt.legend(('numpy fft * dt'), loc='upper right')
  plt.xlabel('f')
  plt.ylabel('amplitude')
  #plt.xlim([0, 1.4])
  
  
  plt.plot(freq[np.argmax(amplitude)], max(amplitude), 'ro')
  print "Amplitude: " + str(max(amplitude)) + "  Frequency: " + str(freq[np.argmax(amplitude)])
  
  plt.show()
  </code></pre>