voltage to decibel

[Disaster_prevention]

Hi

I want to know how to convert the measured sound pressure signal into decibels.

I built an algorithm to convert from voltage to decibel as shown below, but I don't know if it is the right way.

How should the algorithm be modified?

[altenbach]

Decibel  is a relative unit. Where is the reference?

[rolfk]

Assuming that your input signal is in Volts you are currently calculating dBV.  Sound pressure Level is usually defined in Neper and calculated as ln(p/p0) or in dB (re 20uPa) calculated as 20 * log10(p/p0).

p is the pressure of the signal in Pascal and p0 is the reference pressure, usually 20uPa but other references are valid for instance for underwater measurement 1 uPa is often used.

So before you can measure sound pressure you need to calculate the pressure from the voltage which requires you to know the characteristic of your microphone such as uPa/mV and any amplification that happens in between. Also to be completely correct you also need to adjust the pressure at the microphone with the distance to the source which attenuates quadratically with the distance.

Since specified microphone characteristics are usually not very accurate but rather typical specifications you also normally need to perform some form of calibration where you adjust the measured uncalibrated sound pressure level with a calibration. That can be with a well defined signal whose SPL you know or usually with a calibration device that gives you an accurate measurement value to which you can adjust your own measurements.