taking fft of a 500 Hz sine wave signal

[cp617]

Hi, I put together a VI to calculate the FFT of a sine wave signal and graph the result in the frequency domain. In theory, if we take the Fourier Series of a 500Hz sine wave signal, we should see a spike at 500 Hz in the frequency domain. However, the result I got is very noisy and there are spikes everywhere. Could you please take a look at the VI and let me know what is missing?

Thanks  everyone for you help in advance.

[CoastalMaineBird]

You might consider including the WAV file that you read.

[CoastalMaineBird]

Also, consider that the output of the FFT function is complex.

Use a complex-to-polar function on that array to get the magnitude.

[Conseils]

Perhaps this might help... ?

[Nishant]

Hiiii,

             I think you should use the special kit to take the fft, which will give you the perfect answer, here i am attaching a figure,which will show you that how perfect it is by using the special express vis, bcoz they are also given with the sensor sensitivity and ave. paras, which will give u the exact idea.

Thanks,

Nishant

[Nishant]

Hiiii,

             I think you should use the special kit to take the fft, which will give you the perfect answer, here i am attaching a figure,which will show you that how perfect it is by using the special express vis, bcoz they are also given with the sensor sensitivity and ave. paras, which will give u the exact idea.

i forgot to attach the figure in last response.

Thanks,

Nishant

Message Edited by Nishant on 01-26-2006 10:08 PM

[cp617]

Thanks everyone for your speedy replies. I can't open the VI from Conseils because I'm still using LabVIEW 6.1. The graph from Nishant's example is what I'm looking for. Nishant, could you attach your VI as well? thanks.

I'm using the 500 Hz wave file as an example. The actual data that will be fed to the VI is coming from the NI 4472 card, which is taken from a speaker of an external device. What I'm trying to do is: Play a sine wave signal in an external device. Then, capture the audio and check to see if there was a pop or a click in the audio. 

Thanks again for your help.

CP

[Conseils]

Hi, what I was trying to recommend was that you use the power spectrum VI, I belive that you will get what you are expecting, that's what is in the prevois file I posted. I will try to convert it for you later today.

I looked at your WAV file briefly and it looks fine, just like the synthesised version that I included in the ZIP file (that file was software generated) I assume that the file you posted was also software generated.


Regards

[Nishant]

Hiii,cp

              It is glad that it is helpful to you and here i am also attaching a vi, but i dont think that you can open it, totaly right, coz u must have the add-on kit called Vibration and moitoring System for this, and another drivers are of my card, from which i am taking the data, i am using the card Ex-92026.

Thanks,

Nishant    

[dyi]

Hey Nishant, this is also what I am looking for, but I am using version 6.1 as well. if the vi isnt compatible, could you upload pictures of the block diagram (with different cases for sequence, case, etc.)? Or explain what must be done to create it