执行fft时获取矩阵而不是数组

Question

我想了解为什么在执行fft时我没有获得数组。我想为每个频率获得一个幅度，但是得到两个幅度。

sample_rate, recording = wav.read("Sample_747.wav") 
fft = np.fft.fft(recording) 
#print sample_rate,recording

def calculate_normalized_power_spectrum(recording, sample_rate):

    fft = np.fft.fft(recording) 
    number_of_samples = len(recording)        
    # sample_length is the length of each sample in seconds
    sample_length = 1./sample_rate 

     frequencies = np.fft.fftfreq(number_of_samples, sample_length)  
     positive_frequency_indices = np.where(frequencies>0) 
     # positive frequences returned by the fft
     frequencies = frequencies[positive_frequency_indices]
     # magnitudes of each positive frequency in the recording
     magnitudes =abs (fft[positive_frequency_indices])

   return frequencies, magnitudes

当我做fft时我得到了

   print fft
    [[ 1644.+0.j  1642.+0.j]
    [ 1642.+0.j  1644.+0.j]
    [ 1639.+0.j  1639.+0.j]
        ..., 
    [ 1704.+0.j  1702.+0.j]
    [ 1703.+0.j  1703.+0.j]
    [ 1701.+0.j  1701.+0.j]]

当我用我的函数显示幅度时，我为每个频率获得两个幅度

      frq,mag =calculate_normalized_power_spectrum(recording, sample_rate)
       print mag
        [[ 1642.  1644.]
        [ 1639.  1639.]
        [ 1638.  1640.]
              ..., 
        [ 2676.  2676.]
        [ 2674.  2676.]
        [ 2671.  2671.]]