docs: def chirp_stimul():
      """ Amplitude modulated chirp signal """
      from scipy.signal import chirp, hilbert
      duration = 1.0
      fs = 256
      samples = int(fs * duration)
      t = np.arange(samples) / fs
      signal = chirp(t, 20.0, t[-1], 100.0)
      signal *= (1.0 + 0.5 * np.sin(2.0 * np.pi * 3.0 * t))
      analytic_signal = hilbert(signal) * 0.5
      ref_abs = np.abs(analytic_signal)
      ref_instantaneous_phase = np.angle(analytic_signal)
      return analytic_signal, ref_abs, ref_instantaneous_phase