EktaNashine07
commented
2 years ago Hi @too-ns
To calculate dBSPL, it should be
dBSPL = 130 – (20*LOG(ABS(PCM_VALUE)/524288)); This is only valid for 20-bit system,
It is not recommended to convert from a single PCM value to a dBSPL value. dBSPL is an RMS value so it should be computed over a full waveform. If you are measuring the peak PCM level of a sine signal then you can roughly compute the RMS by subtracting 3dB. Computing for a random waveform you should first window the signal, calculate the RMS value of that signal within the window and then convert that result to dBSPL.
Some other information: https://en.wikipedia.org/wiki/Sound_pressure#Sound_pressure_level
Best Regards Ekta
I'm trying to calculate sound pressure in dBSPL scale.
I extended the example soundPressureLevel to get the dBSPL by using the following conversion formulas: dbFS = 20 * log10(abs(maxSample - minSample) / DIGITAL_MAX) where DIGITAL_MAX is 524288 (for a signed 20 bit integer). The sample width is 20 bits which is configured using I2S.begin(). For dBSPL conversion, dBSPL = AOP + dbFS where AOP is 130 for IM69D130.
My issue being, when checking for the values in serial plotter/monitor with a reference sound level meter, it seems to be off by 10 dB. I'm using the IM69D130-Microphone-Shield2Go with XMC2GO and using Arduino IDE for compilation and serial data monitoring.
Please comment on the validity of the approach that I've used and suggest a way/resource to proceed to calculate dBSPL.