For Android smartphones, is it possible to set the loudness in decibel for the headphone jack or internal speaker instead of using the percentage Loudness?
I want to produce a sound which loudness is the exact same across all smartphones.
I don't think that'd be possible because decibels is a measurement of how loud something is, so you'd use your microphone to check how loud your music is playing through your speaker not how loud you want it to be.