carrier.py 文件源码

def design(self, fs, fc, n_cycles=7.0, bandwidth=None, zero_mean=True):
        """
        Designs a FIR filter that is a band-pass filter centered
        on frequency fc.
        fs         : sampling frequency (Hz)
        fc         : frequency of the carrier (Hz)
        n_cycles   : number of oscillation in the wavelet
        bandwidth  : bandwidth of the FIR wavelet filter
                     (used when: bandwidth is not None and n_cycles is None)
        zero_mean  : if True, we make sure fir.sum() = 0
        """
        # the length of the filter
        if bandwidth is None and n_cycles is not None:
            half_order = int(float(n_cycles) / fc * fs / 2)
            order = 2 * half_order + 1
        elif bandwidth is not None and n_cycles is None:
            half_order = int(1.65 * fs / bandwidth) // 2
            order = half_order * 2 + 1
        else:
            raise ValueError('Carrier.design: n_cycles and order cannot be '
                             'both None or both not None.')

        w = np.blackman(order)
        t = np.linspace(-half_order, half_order, order)
        phase = (2.0 * np.pi * fc / fs) * t

        car = np.cos(phase)
        fir = w * car

        # the filter must be symmetric, in order to be zero-phase
        assert np.all(np.abs(fir - fir[::-1]) < 1e-15)

        # remove the constant component by forcing fir.sum() = 0
        if zero_mean:
            fir -= fir.sum() / order

        gain = np.sum(fir * car)
        self.fir = fir * (1.0 / gain)
        self.fs = fs

        # add the imaginary part to have a complex wavelet
        if self.extract_complex:
            car_imag = np.sin(phase)
            fir_imag = w * car_imag
            self.fir_imag = fir_imag * (1.0 / gain)

        return self