text: import collections
  
  from supriya import CalculationRate
  from supriya.synthdefs import UGen
  
  
  class ZeroCrossing(UGen):
      """
      A zero-crossing frequency follower.
  
      ::
  
          >>> source = supriya.ugens.In.ar(bus=0)
          >>> zero_crossing = supriya.ugens.ZeroCrossing.ar(
          ...     source=source,
          ...     )
          >>> zero_crossing
          ZeroCrossing.ar()
  
      """
  
      ### CLASS VARIABLES ###
  
      __documentation_section__ = "Analysis UGens"
  
      _ordered_input_names = collections.OrderedDict([("source", None)])
  
      _valid_calculation_rates = (CalculationRate.AUDIO, CalculationRate.CONTROL)
  