How to calculate dBSPL from sound level

[riyolu]

Hello all,

I have a question regarding the MEMS audio sensor MP23DB01HP. I managed to read out the Soundlevel of the sensor. But I don't know how to interpret this value. My question is, how can I convert the soundlevel to obtain a corresponding value in dB? Is the datasheet needed for that conversion?

Thank you in advance for your replies

[AG.8]

Hi @riyolu​ , usually the microphone full scale is calculated starting from the AOP (acoustic overload point). Ideally, it refers to a saturated (square) wave. For the MP23DB01HP the value is 135dBSPL, so the PCM value you get from the PDM has to be scaled according to this value.

This documentation might help you:

https://www.st.com/resource/en/user_manual/um2372-stm32cube-pdm2pcm-software-library-for-the-stm32f4f7h7-series-stmicroelectronics.pdf

https://www.youtube.com/watch?v=_YQSJJQUp-g

AG

[riyolu]

Hi @AG.8​ , thank you for your answer. I recently found out, that I can calculate the dBFS value with the formula:

20 * log10 (x / fs)

with 'x' being the measured soundlevel and 'fs' being the maximal possible soundlevel, i.e. 20 * log10(fs) = AOP. Hence, the formula given above returns the difference of the AOP to the currently measured soundlevel. My question is, how can I find out 'fs'? With that knowledge, it should be possible to calculate the current soundlevel in dBSPL.