def _setup_freqs(self):
        """Updating frequency borders from channel values
        """

        if self.header[b'foff'] > 0:
            self.f_start = self.f_begin + self.chan_start_idx*abs(self.header[b'foff'])
            self.f_stop = self.f_begin + self.chan_stop_idx*abs(self.header[b'foff'])
        else:
            self.f_start = self.f_end - self.chan_stop_idx*abs(self.header[b'foff'])
            self.f_stop = self.f_end - self.chan_start_idx*abs(self.header[b'foff'])
Updating frequency borders from channel values