# How to calculate sound pressure levels using microphone sensitivity rating

This is sort of a cross between a computer science and Physics question, but I would be grateful if anyone here could help me.

My objective is to calculate the sound pressure level (in dB) of a sound generated 1 meter away. I don't have a SPL meter, nor do I have the money to buy one, so I would like to use my condenser microphone to calculate this. The microphone I have is the Blue Yeti, which has a sensitivity of 4.5mV/Pa (reference value 20 microPascal).

So my question is is there a way that the digital output of the microphone can be directly monitored and recorded in units of Volts. Hence, I would use these values to calculate Pascals and then dB. Can anyone point me to a (preferably free) program that can do this?

Also please feel free to comment on my experimental method. Is my reasoning in calculating the SPA sound when it comes to this?

• If you can establish the sensitivity of your computer input, not a problem, but I wouldn't expect particularly precise results. Absolute acoustic measurements are notoriously hard. NIST has some rather nice articles about the subject here: nist.gov/calibrations/acoustic_measurements.cfm Commented Jun 28, 2016 at 5:40
• How would one go about finding the sensitivity of their computer input? Also, the measurements do not have to be precise, I'm fine with a rough estimate of the voltage output. Thanks for the help! Commented Jun 28, 2016 at 5:43
• I have oscilloscopes etc. with the proper calibration, which makes this easy. Without that I would start with a voltage reference (e.g. an LT1019 linear.com/product/LT1019), which I would chop to a 1kHz square wave using a CMOS switch/multiplexer, add a buffer opamp and a variable voltage divider made from 0.1% resistors (possibly selected down to 0.01% of relative tolerance), then another opamp buffer to counteract the load impedance of the input stage. This will get you to absolute AC signals with better than 1% voltage error to calibrate the response of the computer input. Commented Jun 28, 2016 at 5:50