import pyfar as pf
signal = pf.signals.impulse(4096)
signal = pf.dsp.filter.bell(signal, 1e3, 20, 1)
soft = pf.dsp.soft_limit_spectrum(signal, limit=10, knee=12)
hard = pf.dsp.soft_limit_spectrum(signal, limit=10, knee=0)
pf.plot.freq(soft, label='soft (knee > 0)')
pf.plot.freq(hard, label='hard (knee = 0)')
ax = pf.plot.freq(signal, ls='--', label='original')
ax.set_ylim(-5, 25)
ax.legend()