Microphone calibratrion for dB reading from pc sound card?

[Halla]

We are trying to acquire a sound signal from a regular laptop sound card into labview, and obtain a sound intensity reading and a frequency reading. Through FFT we are able to acquire the strongest signal, but the dB readings are all over the map. Using a sound generator we were able to conclude the frequency readings were indeed correct, but the sound intensity was way off, and non-repeatable. So what I'm looking to know is if it is possible to calibrate the mic within labview or to read in a sound level measurement in dB with a regular PC mic and sound card. Even if it was a gain measurement, how do set the baseline for 0 dB? Please help!

thanks

Adrien Samson

Halla Climate Control INC

[AESulzer]

Adrien,

I'm confused with your setup. How are you acquiring this sound signal? Which measurements/calculations are occurring outside of LabVIEW and which are occurring inside of LabVIEW? Is the problem you are having with LabVIEW VIs or with hardware calibration? Answering these questions and elaborating more might help myself and others better help you.

Kind Regards,

[duende]

Hi both. I'm trying to develop a cheap sound intensity probe, i alredy builded it but im a litle lost in developing the acquisition software. Any sugestion? Thanks!!

Peter

[CKap]

Hello Peter,

If you want to acquire sound using a mic, then you could use the Sound API. The VIs for this API could be found on the function palette at Programming >> Graphics & Sound >> Sound >> Input.

Look out for examples in the example finder.

Regards,

Chetan K

Application Engineer

NI

[Przemyslaw]

I have a similar problem.
I want to measure a sound through my sound card in my computer. For this purpose I use ready-made examples: "SVXMPL_Getting started with SVT (Simulated). Vi" and "input Suond this file".
The system lies in the fact that I record wav and then analyze it with the first example.
Problem lies in the analyzer calibration or anything.
I have a acuostical calibrator so I know the level of sound and after recording and analyzing get too low results.
What should I do to correct this?

[rolfk]

A computer sound card is simply a low cost audio input/output. Low cost means that it has usually no calibration options at all, and even if it had, Windows would not know how to access it and even less so allow an application to use it through a known API.

So you have to do your calibration yourself in software. The way that works is to apply a known signal, measure the sound signal in Volts and then calculate a calibrarion function that translates those Volt into the dB you know you have applied. Additional problems could be that the analog path on your sound card is good enough for the human ear, but totally useless for measurement purposes, since the amplifier transfer function is anything but constant over the frequency range. Also sound measurements with cheap microphones is another big problem, since those microphones are at best a guessimator, but no accurate measurement device.

Basically you have to do the calibration repeatedly at the same frequency and also at various frequencies too, in order to see if the microhone is actually useful at all (repeatability of calibration value at the same frequency), as well as reasonaby constant over the frequency range for both the mic and the sound card.

With most standard sound cards none of this is a given, and unless you also use a really good microphone, even the most accurate sound card can't do much for you.

[Przemyslaw]

THX

Przemek