docs: def _enhance_bass(self):
          """Update best span choices with bass enhancement as requested by user (Eq. 11)."""
          if not self._bass_enhancement:
              # like in supsmu, skip if alpha=0
              return
          bass_span = DEFAULT_SPANS[BASS_INDEX]
          enhanced_spans = []
          for i, best_span_here in enumerate(self._best_span_at_each_point):
              best_smooth_index = DEFAULT_SPANS.index(best_span_here)
              best_span = DEFAULT_SPANS[best_smooth_index]
              best_span_residual = self._residual_smooths[best_smooth_index][i]
              bass_span_residual = self._residual_smooths[BASS_INDEX][i]
              if 0 < best_span_residual < bass_span_residual:
                  ri = best_span_residual / bass_span_residual
                  bass_factor = ri ** (10.0 - self._bass_enhancement)
                  enhanced_spans.append(best_span + (bass_span - best_span) * bass_factor)
              else:
                  enhanced_spans.append(best_span)
          self._best_span_at_each_point = enhanced_spans