def _setup_freqs(self, f_start=None, f_stop=None):
<EOL>f0 = self.header[b'<STR_LIT>']<EOL>f_delt = self.header[b'<STR_LIT>']<EOL>i_start, i_stop = <NUM_LIT:0>, self.header[b'<STR_LIT>']<EOL>if f_start:<EOL><INDENT>i_start = int((f_start - f0) / f_delt)<EOL><DEDENT>if f_stop:<EOL><INDENT>i_stop  = int((f_stop - f0)  / f_delt)<EOL><DEDENT>chan_start_idx = np.int(i_start)<EOL>chan_stop_idx  = np.int(i_stop)<EOL>if i_start < i_stop:<EOL><INDENT>i_vals = np.arange(chan_start_idx, chan_stop_idx)<EOL><DEDENT>else:<EOL><INDENT>i_vals = np.arange(chan_stop_idx, chan_start_idx)<EOL><DEDENT>self.freqs = f_delt * i_vals + f0<EOL><INDENT>if f_delt < <NUM_LIT:0>:<EOL><INDENT>self.freqs = self.freqs[::-<NUM_LIT:1>]<EOL><DEDENT><DEDENT>if chan_stop_idx < chan_start_idx:<EOL><INDENT>chan_stop_idx, chan_start_idx = chan_start_idx,chan_stop_idx<EOL><DEDENT>return i_start, i_stop, chan_start_idx, chan_stop_idx<EOL>
Setup frequency axis