def _plot_filter(b, a, sampling_rate=1000., nfreqs=4096, ax=None):
"""Compute and plot the frequency response of a digital filter.
Parameters
----------
b : array
Numerator coefficients.
a : array
Denominator coefficients.
sampling_rate : int, float, optional
Sampling frequency (Hz).
nfreqs : int, optional
Number of frequency points to compute.
ax : axis, optional
Plot Axis to use.
Returns
-------
fig : Figure
Figure object.
"""
# compute frequency response
freqs, resp = st._filter_resp(b,
a,
sampling_rate=sampling_rate,
nfreqs=nfreqs)
# plot
if ax is None:
fig = plt.figure()
ax = fig.add_subplot(111)
else:
fig = ax.figure
# amplitude
pwr = 20. * np.log10(np.abs(resp))
ax.semilogx(freqs, pwr, 'b', linewidth=MAJOR_LW)
ax.set_ylabel('Amplitude (dB)', color='b')
ax.set_xlabel('Frequency (Hz)')
# phase
angles = np.unwrap(np.angle(resp))
ax2 = ax.twinx()
ax2.semilogx(freqs, angles, 'g', linewidth=MAJOR_LW)
ax2.set_ylabel('Angle (radians)', color='g')
ax.grid()
return fig
def _plot_filter(b, a, sampling_rate=1000., nfreqs=512, ax=None):
"""Compute and plot the frequency response of a digital filter.
Parameters
----------
b : array
Numerator coefficients.
a : array
Denominator coefficients.
sampling_rate : int, float, optional
Sampling frequency (Hz).
nfreqs : int, optional
Number of frequency points to compute.
ax : axis, optional
Plot Axis to use.
Returns
-------
fig : Figure
Figure object.
"""
# compute frequency response
freqs, resp = st._filter_resp(b, a,
sampling_rate=sampling_rate,
nfreqs=nfreqs)
# plot
if ax is None:
fig = plt.figure()
ax = fig.add_subplot(111)
else:
fig = ax.figure
# amplitude
ax.semilogy(freqs, np.abs(resp), 'b', linewidth=MAJOR_LW)
ax.set_ylabel('Amplitude (dB)', color='b')
ax.set_xlabel('Frequency (Hz)')
# phase
angles = np.unwrap(np.angle(resp))
ax2 = ax.twinx()
ax2.plot(freqs, angles, 'g', linewidth=MAJOR_LW)
ax2.set_ylabel('Angle (radians)', color='g')
ax.grid()
return fig