SNR measurement VI?

[MVK]

Hello anyone can provide me a Signal-to-Noise-Ratio (SNR) measurement VI?

Note: I am using PXI 4461 for this process. i want to find out the ratio between signal and true noise(no harmonics)

[dsb@NI]

You can compute the energy of the "true noise" by taking the difference between the total energy in the signal and the energy in the fundamental and harmonics.

You can compute the result from measurements of THD+N and THD by the following equation:
THD+N = THD - SNR

-85.0 dB = -90.0 dB - (SNR) --> SNR = 86.65 dB

The following website hosts a utility to do the math in dB. They use SINAD instead of THD+N (SINAD is the inverse of THD+N)
http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/utility/snr.html

Repost if you have any questions about using THD+N and THD to compute SNR. Will you exclude energy associated with DC from the measurement?

[MVK]

Hello Doug Bendele,
This is a reliable source of information. Thanks a lot for your suggestion. I have made a VI according to your idea. Please find the attachment. In the attachment you can find a VI. Actually what I have done in that VI means, " I am generating a signal at 1KHz frequency using analog output channel. Then I am taking back that signal feeding in to analog input channel. Further I measuring SNR according to your suggestion.” Why I am doing all these means, my application is like this…. “An audio signal is coming out from UUT (unit under test) I have to find out SNR of that signal” right now I don’t have UUT with me. It is actually in the site. So just for trail I am generating audio signal using PXI 4461 then I am taking back to analog input of the same card. For all above process I am using PXI 4461 DSA card. Please make me sure about my procedure to find out SNR of a audio signal. If any thing wrong in my procedure please let me know.

Note: In the block diagram of the VI you can find a vi named as SNR formula. Please check out that vi feeding different number of THD+N & THD and find out SNR. If any thing wrong in this calculation please make me correct.

[dsb@NI]

I could not find the VI, SNR formula.vi, in your last post. I am a little dubious of the VI that I found because it seems as though it takes the inverse (1/x) of the SINAD (dB). Math with quantities in log scale can be tricky. Please attach the SNR formula.vi, and I will verify the math.

Doug Bendele
Sound and Vibration Applications
National Instruments

[MVK]

Dear Doug Bendele
Sorry i was outof station past 10 days. That is the reason i am replying late. Now i have attached SNR formula vi with this mail. I am doubting about my SNR calculation. Somewhere i am doing mistake. Pls give me your suggesstion
Thank you.

[Anu]

Dear Doug Bendele

We have some issue in SNR calculation,we need both VI to be Tested,Since these Two VI satisfy the calculation

 -85.0 dB = -90.0 dB - (SNR) --> SNR = 86.65 dB
Though theoritical value are Ok,we face issue when compare with SNR value from client standalone instruments,we want to know,is there any other factor affects SNR measurement or problem in log math.If any thing wrong in this  procedure please let me know.

 

[dsb@NI]

The attached VI can be used in conjunction with the Distortion Express VI. Wire the outputs for SINAD (dB) and THD from the Express VI to SNR formula_modified for Express.vi. There are several factors that would come into play when comparing SNR measurements from different devices: 1. algorithm 2. frequency range 3. harmonics included? and how many? 4. hardware accuracy (in measuring the fundamental, harmonics, and noise floor) ...

[Mikhail Arriaczemko]

Hi everyone!

Before everything receive best regards! I am looking for a way to measure SNR. According to the theory we´ve studied, we need to compute the power of the clean signal and divide it by the power of the noise alone. However, and please, excuse my ignorance, I´m new with LabView, so there´re many things I still ignore how to do, among those, computing a power value and work with it. If I can measure power, i.e., obtain an instant value, I could probably compute SNR.

In addition, I would like to know how to obtain SNR before and after a Demodulation proces (bot AM and FM), to obtain a "Merit Factor" (I don´t know if this expression holds in english, but in spanish is "Factor de Mérito"), which is SNR(In)/SNR(Exit), and this value shows the quality of the demodulation process.

Thanks in Advance, and please, if you can, send  a copy of your reply to: eoarria@gmail.com, you can send all the vi´s you consider may help me to learn how to work with SNR (I Just started learning how to use Labview a week ago!). THANKS!

[indicates required information.]

Hello anyone can provide me a Signal-to-Noise-Ratio (SNR) measurement VI?

Can you help me please?

[dsb@NI]

The attached picture shows how you can use the VI attached in an earlier post to compute SNR from the SINAD and THD outputs of the LabVIEW Distortion Express VI.

Also, there is a product, the Sound and Vibration Toolkit, that ships with VIs to measure SNR and many other forms of distortion. The SNR measurement in the Sound and Vibration Toolkit also supports additional measurement parameters to band limit the measurement to the desired frequency range as well as account for varying amounts of phase noise. These measurement parameters can significantly affect the measured SNR. If your signal is characterized by a pure fundamental tone, low distortion (THD within 20 dB of computed SNR), and low out-of-band noise, use the previously attached VI in conjunction with the LabVIEW Distortion Express VI. If your signal exhibits phase noise, relatively high harmonic distortion, or high out-of-band noise; or your application will also need additional distortion measurements or additional spectral measurements, take a look at the features in the Sound and Vibration Toolkit.