Plot Frequency Response of FIR

FIRSpectrumSimple.py

# -*- coding: utf-8 -*-

# Sampling frequency
fs = 44100
# FFT size
N = 32768
# use Log freq response ? (False: Linear)
logFreq = False
# normalize peak to 0dB ?
peakAtZero = False

import numpy as np
import matplotlib.pyplot as plt
np.set_printoptions(precision=15, suppress=True)


def fir_freqz(b):
    X = np.fft.fft(b, N)
    Xm = np.abs(X)
    if peakAtZero:
        Xdb = 20*np.log10(Xm/Xm.max())
    else:
        Xdb = 20*np.log10(Xm)
    f = np.arange(N)*fs/N
    return Xdb, f
       
if __name__ == "__main__":

    # FIR filter coefficients
    
    b = np.array([-1, 
     2.847, -4.685,  6.214,
	-7.184, 6.639, -5.032,
	3.263, -1.632, 0.4191
      ])
                  
    Xdb, f = fir_freqz(b)       
    plt.clf()

    # Plot the frequency response
    if logFreq:
        plt.semilogx(f, Xdb, 'b')
    else:
        plt.plot(f, Xdb, 'b')
    
    plt.grid(True)
    plt.hold(True)
    plt.title('Frequency reponse')
    plt.xlabel('Frequency [Hz]')
    plt.ylabel('Amplitude [dB]')
    plt.xlim((0, fs/2))
    plt.legend()
    plt.savefig('e:\\t\\foo.png', bbox_inches='tight')
    plt.show()