Different signal to noise ratio

[candyuco]

Hi,

My project is to generate a sine wave signal, use a DAQ device to receive the generated signal, and measure the signal to noise ratio of the received signal after using C-weighting filter. However, I got different SNR values when I used Tone measurement, SNR without harmonics.vi and Noise measurement. Does anyone know the difference in calculating SNR by using those 3.

Btw, the unit of SNR in Tone measurement is dBc, does it mean the result already used C-weighting filter?

Thank you

[snowpunter]

dBc means relative to the amplitude of the carrier. It has nothing to do with the weighting.

You should probably take a look here:

http://zone.ni.com/devzone/cda/epd/p/id/5640

[candyuco]

Thank you snowpunter, I'm trying to understand the link you sent me. I'll need youe help if I can't figure out.

[candyuco]

Hi Snowpunter,

I still got different values for SNR. Do you know the differences in the methods those VIs used? They had same definitions "signal to noise ratio (SNR) defined as the ratio of the root-mean-square (RMS) energy of the fundamental tone to the RMS energy of the noise".

Thanks for your help.