How can I calculate audio dB level?

Question

I want to calculate room noise level with the computer\'s microphone. I record noise as an audio file, but how can I calculate the noise dB level?

I don\'t know how

Answer 1

According to Merchant et al. (section 3.2 in the appendix: "Measuring acoustic habitats", Methods in Ecology and Evolution, 2015), you can actually calculate absolute, calibrated SPL values using manufacturer specifications by subtracting a correction term S to your relative (scaled to maximum) SPL values:

S = M + G + 20*log10(1/Vadc) + 20*log10(2^Nbit-1)

where M is the sensitivity of the transducer (microphone) re 1 V/Pa. G is the gain applied by the user. Vadc is the zero-to-peak voltage, given by multiplying the rms ADC voltage by a conversion factor of squareroot(2). Nbit is the bit sampling depth.

The last term is necessary if your system scales the amplitude by its maximum.

The correction will be more accurate using end-to-end calibration with sound calibrators.

Note that the formula above is dependent on frequency, but you could apply it over a wider frequency range if your microphone has a flat frequency response.