This app needs root! If you don't know what root is, don't even try this app
***The app works by editing a system file, mixer_paths.xml, that is different between devices, and many devices don't even have (and that's where all these bad reviews come from), so every device can have different results, and some values may not show up or the app may not work at all.
I tested on Nexus 5 and OnePlus 5, I am always available for refund, contact me by e-mail in that case***
Your speaker or headphones* aren't loud enough? (or are too loud)
You want to record gigs or any loud event but your microphone* crackles destroying every audio detail?
Or you have to shout during calls because microphones* aren't sensitive enough?
In any of these cases, this app may be exactly what you search for.
*features of pro version, the free one lets you tweak speaker only.
**I'm not responsible of any damage made to your device or your ears, tweak values progressively**