I'm trying to find a completely free app to increase the volume of a previously recorded voice recor

[Android Central Question]

I have tried and installed dozens of applications that claim to raise the volume of a voice or other recorded sound that is virtually inaudible after being recorded with a highly recommended voice recorder app., but none actually have a function to increase the volume of the previously recorded sound. Can anyone recommend a completely free app that will perform this function so that I can add the voice/sound to a video I wish to upload?

 

[pkcable]

This is what I have used on low sounding devices.....

https://play.google.com/store/apps/details?id=us.doda.volume.booster&hl=en_US