how to distort soundtrack without affecting timeline

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Of all the video editing software I tried on my old Pentium 4 PC, Corel Video Studio had the snappiest performance but it was still quite slow and choppy when working with 720p/60fps MP4s and I didn't really get a chance to explore its features in much detail before the trial expired. I'm getting a new faster PC. But in the meantime, I have a question.

Here's what I'm hoping to do: I have videos of my son's high school soccer games, and some of the other parents have asked me for copies. I would like to find a way to garble the conversations and remarks of people who were standing near me as I filmed, so what they are saying cannot be understood. It also has to be done in a way that the original conversations could not be easily reverse-engineered by removing a filter. I really don't want these "overheard" conversations and remarks to be intelligible. Some of the things being said would not have been said had the speakers been aware that they were being recorded for posterity! My camera is about the size of a cell phone and is inconspicuous.

However, in distorting the sounds of speech I'd hope that the cheering of the crowd could remain at least recognizable as the sound of cheering, even if it too has been distorted. I also don't want to screw up the timing: the cheering should occur at the right times. I don't want to replace the soundtrack with music or silence, and there won't be enough time to edit the footage piecemeal, editing out the conversations. Hoping to run the entire soundtrack through this process.

Is there any audio processing plug-in for Video Studio that could permanently create this garbled-speech distortion effect? Or would I have to search for a standalone audio-effects package, edit the MP4 soundtrack with it, and then bring the edited MP4 into the Video Studio library? If there's a name for this sort of thing, please tell me.

Thanks