There are free recording programs/websites I've found that will let you record and manipulate your voice - slow/speed up, change pitch, volume, etc. In one such presentation that had to be recorded due to time zone differences, I recorded the audio for each slide, and used this website to save, and embed the revised clip in each PPT slide. I spoke very slowly & dliberately into the mic, and then sped up the saved audio file 2x to make it sound more natural. [https://online-voice-recorder.com/](https://online-voice-recorder.com/)