tonek — A first-order recursive low-pass filter with variable frequency response.
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.
kres -- the output signal at control-rate.
ksig -- the input signal at control-rate.
khp -- the response curve's half-power point, in Hertz. Half power is defined as peak power / root 2.
tonek is like tone except its output is at control-rate rather than audio rate.