Volume Booster Pro uses your built-in Android eQ to adjusts the frequencies of your device and makes it louder.
We use the new loudness module on device above Android 4.3 which is running behind the Boost button.
Listen the song and spot the difference. Make sure to tap a few times the play/stop button to spot the best results.
Older version should use the slider only.
For maximum results use external speakers or headsets.
Ringtone: https://goo.gl/A5SU6B

Listening music too loud is bad for your ears.