audio - Calculate Decibel from amplitude - Android media recorder

Question

How to calculate decibel from maxAmplitude, I wrote an android application to get maxAmplitude at regular interval, I need to show the o/p to the user in decibels.

Answer 1

Decibels are a relative unit, they express the power of your signal relative to some reference power.

If you are working with amplitudes, then the formula is:

power_db = 20 * log10(amp / amp_ref);

(See http://en.wikipedia.org/wiki/Decibel#Field_quantities).

Note also that maximum amplitude is not usually a very good indicator of loudness (or even of power). More typically, you should measure the RMS power of your signal, and convert that to dB instead.