Export to Frequency, Time, Amplitude file.
        Frequency is double, Time (nanosecond) is uint32, Amplitude is float32

        :return:

def export_to_fta(self, sample_rate, filename: str, include_amplitude=False):
        """
        Export to Frequency, Time, Amplitude file.
        Frequency is double, Time (nanosecond) is uint32, Amplitude is float32

        :return:
        """
        spectrogram = self.__calculate_spectrogram(self.samples)
        spectrogram = np.flipud(spectrogram.T)
        if include_amplitude:
            result = np.empty((spectrogram.shape[0], spectrogram.shape[1], 3),
                              dtype=[('f', np.float64), ('t', np.uint32), ('a', np.float32)])
        else:
            result = np.empty((spectrogram.shape[0], spectrogram.shape[1], 2),
                              dtype=[('f', np.float64), ('t', np.uint32)])

        fft_freqs = np.fft.fftshift(np.fft.fftfreq(spectrogram.shape[0], 1/sample_rate))
        time_width = 1e9 * ((len(self.samples) / sample_rate) / spectrogram.shape[1])

        for i in range(spectrogram.shape[0]):
            for j in range(spectrogram.shape[1]):
                if include_amplitude:
                    result[i, j] = (fft_freqs[i], int(j*time_width), spectrogram[i, j])
                else:
                    result[i, j] = (fft_freqs[i], int(j * time_width))

        result.tofile(filename)