问题:

Please help me calculate decibels from phone microphone. The microphone has a getMaxAmplitude() function. How I can I use it to calculate decibels? I read in some forums that the decibel calculation formula is power_db = 20 * log10(amplitude / reference_amplitude). But I don't understand how to find the reference_amplitude.

回答1:

Decibels are a unit widely used to define some quantity relative to something else. There are a number of different types of decibel measurements, depending on what you're trying to describe about the signal you're receiving.

Read this link to get you started, it explains everything you need to know much better than I can!

回答2:

In sound, decibel values are referenced to a sound pressure level of 20µPa (20 micro Pascal). So in your case the reference_amplitude would be the amplitude generated by your microphone in the presence of a sound field with a level of 20µPa.

In practice, to find this level, microphones are often calibrated (using a microphone calibrator) with a signal of some precisely known level (often around 94dB). The amplitude resulting from this calibration signal can then be used to calculate the amplitude for the reference signal (assuming the response of the microphone is linear).