Without knowing the specific headphones you're using, your phone can't really tell you loud it is because it depends on the impedance and sensitivity of the headphones.
I assume this is an app for a specific set of (Bluetooth) headphones.
Without knowing the specific headphones you're using, your phone can't really tell you loud it is because it depends on the impedance and sensitivity of the headphones.
I assume this is an app for a specific set of (Bluetooth) headphones.