code: def generate_with_delta_f_and_max_freq(self, t_num, max_freq, delta_f,
                                             low_frequency_cutoff=None,
                                             cached_mem=None):
          
          approximant = self.approximant(t_num)
          # Don't want to use INTERP waveforms in here
          if approximant.endswith('_INTERP'):
              approximant = approximant.replace('_INTERP', '')
          # Using SPAtmplt here is bad as the stored cbrt and logv get
          # recalculated as we change delta_f values. Fall back to TaylorF2
          # in lalsimulation.
          if approximant == 'SPAtmplt':
              approximant = 'TaylorF2'
          if cached_mem is None:
              wav_len = int(max_freq / delta_f) + 1
              cached_mem = zeros(wav_len, dtype=np.complex64)
          if self.has_compressed_waveforms and self.enable_compressed_waveforms:
              htilde = self.get_decompressed_waveform(cached_mem, t_num,
                                                      f_lower=low_frequency_cutoff,
                                                      approximant=approximant,
                                                      df=delta_f)
          else :
              htilde = pycbc.waveform.get_waveform_filter(
                  cached_mem, self.table[t_num], approximant=approximant,
                  f_lower=low_frequency_cutoff, f_final=max_freq, delta_f=delta_f,
                  distance=1./DYN_RANGE_FAC, delta_t=1./(2.*max_freq))
          return htilde
docs: Generate the template with index t_num using custom length.