iskip (optional, default=0) -- initial disposition of internal data space. Since filtering incorporates a feedback loop of previous output, the initial status of the storage space used is significant. A zero value will clear the space; a non-zero value will allow previous information to remain. The default value is 0.
ar -- the output audio signal.
asig -- the input audio signal.
khp -- the response curve's half-power point, in Hertz. Half power is defined as peak power / root 2.
tone implements a first-order recursive low-pass filter in which the variable khp (in Hz) determines the response curve's half-power point. Half power is defined as peak power / root 2.