From low-pass to normal and vice-versa?

I want to know (how) can I do on Audacity or FL Studio this effect:

  1. Duplicate the track (Ctrl+D)
  2. Apply Low Pass filter to the duplicate
  3. Apply Fade Out to the first half of the original track and Fade In to the second half.
  4. Apply Fade In to the first half of the duplicate track and Fade Out to the second half.

For more complex changes you can use the “Adjustable Fade” effect or the Envelope Tool

If you want the effect to change differently in the left and right channels of a stereo track, split the stereo track into separate Left and Right tracks, then use the above technique on each track (see:

Thank you, I think it works like it used to work now.