import pyfar as pf
import matplotlib.pyplot as plt
lower, upper, frequencies = \
    pf.constants.fractional_octave_filter_tolerance(
        exact_center_frequency=1000, num_fractions=1,
        tolerance_class=1)
octave_filter = pf.dsp.filter.fractional_octave_bands(
    pf.signals.impulse(2**12), num_fractions=1,
    frequency_range=(1000, 1000))
ax = pf.plot.freq(octave_filter, color='k', label='Octave filter')
plt.fill_between(
    frequencies, lower, upper,
    facecolor='g', alpha=.25, label='Class 1 Tolerance')
ax.set_ylim(-70, 5)
ax.set_xlim(63, 15_850)
ax.legend()