def freqz_resp_list(b,a=np.array([1]),mode = 'dB',fs=1.0,Npts = 1024,fsize=(6,4)):
    """
    A method for displaying digital filter frequency response magnitude,
    phase, and group delay. A plot is produced using matplotlib

    freq_resp(self,mode = 'dB',Npts = 1024)

    A method for displaying the filter frequency response magnitude,
    phase, and group delay. A plot is produced using matplotlib

    freqz_resp(b,a=[1],mode = 'dB',Npts = 1024,fsize=(6,4))

        b = ndarray of numerator coefficients
        a = ndarray of denominator coefficents
     mode = display mode: 'dB' magnitude, 'phase' in radians, or 
            'groupdelay_s' in samples and 'groupdelay_t' in sec, 
            all versus frequency in Hz
     Npts = number of points to plot; default is 1024
    fsize = figure size; defult is (6,4) inches

    Mark Wickert, January 2015
    """
    if type(b) == list:
        # We have a list of filters
        N_filt = len(b)
    f = np.arange(0,Npts)/(2.0*Npts)
    for n in range(N_filt):
        w,H = signal.freqz(b[n],a[n],2*np.pi*f)
        if n == 0:
            plt.figure(figsize=fsize)
        if mode.lower() == 'db':
            plt.plot(f*fs,20*np.log10(np.abs(H)))
            if n == N_filt-1:
                plt.xlabel('Frequency (Hz)')
                plt.ylabel('Gain (dB)')
                plt.title('Frequency Response - Magnitude')

        elif mode.lower() == 'phase':
            plt.plot(f*fs,np.angle(H))
            if n == N_filt-1:
                plt.xlabel('Frequency (Hz)')
                plt.ylabel('Phase (rad)')
                plt.title('Frequency Response - Phase')

        elif (mode.lower() == 'groupdelay_s') or (mode.lower() == 'groupdelay_t'):
            """
            Notes
            -----

            Since this calculation involves finding the derivative of the
            phase response, care must be taken at phase wrapping points 
            and when the phase jumps by +/-pi, which occurs when the 
            amplitude response changes sign. Since the amplitude response
            is zero when the sign changes, the jumps do not alter the group 
            delay results.
            """
            theta = np.unwrap(np.angle(H))
            # Since theta for an FIR filter is likely to have many pi phase
            # jumps too, we unwrap a second time 2*theta and divide by 2
            theta2 = np.unwrap(2*theta)/2.
            theta_dif = np.diff(theta2)
            f_diff = np.diff(f)
            Tg = -np.diff(theta2)/np.diff(w)
            # For gain almost zero set groupdelay = 0
            idx = np.nonzero(np.ravel(20*np.log10(H[:-1]) < -400))[0]
            Tg[idx] = np.zeros(len(idx))
            max_Tg = np.max(Tg)
            #print(max_Tg)
            if mode.lower() == 'groupdelay_t':
                max_Tg /= fs
                plt.plot(f[:-1]*fs,Tg/fs)
                plt.ylim([0,1.2*max_Tg])
            else:
                plt.plot(f[:-1]*fs,Tg)
                plt.ylim([0,1.2*max_Tg])
            if n == N_filt-1:
                plt.xlabel('Frequency (Hz)')
                if mode.lower() == 'groupdelay_t':
                    plt.ylabel('Group Delay (s)')
                else:
                    plt.ylabel('Group Delay (samples)')
                plt.title('Frequency Response - Group Delay')
        else:
            s1 = 'Error, mode must be "dB", "phase, '
            s2 = '"groupdelay_s", or "groupdelay_t"'
            print(s1 + s2)
A method for displaying digital filter frequency response magnitude,
    phase, and group delay. A plot is produced using matplotlib

    freq_resp(self,mode = 'dB',Npts = 1024)

    A method for displaying the filter frequency response magnitude,
    phase, and group delay. A plot is produced using matplotlib

    freqz_resp(b,a=[1],mode = 'dB',Npts = 1024,fsize=(6,4))

        b = ndarray of numerator coefficients
        a = ndarray of denominator coefficents
     mode = display mode: 'dB' magnitude, 'phase' in radians, or 
            'groupdelay_s' in samples and 'groupdelay_t' in sec, 
            all versus frequency in Hz
     Npts = number of points to plot; default is 1024
    fsize = figure size; defult is (6,4) inches

    Mark Wickert, January 2015