Perform FFT on stationary signal

so once i capture all my data (mains 50Hz) and i want to perform an FFT on it, how do i then do it while its stationary. ive almost got some code finished, however, its still going to be streaming isnt it?. i need to make stationary. any advice?
cheers.

You can accumulate data in a buffer until you reach the amount of data you want to analyze. Then clear the buffer and start over. Or you can use the Point-by-Point VIs which will do the accumulation for you. If you open the PtbyPt VIs you will find that they build an internal buffer.
Lynn

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Display FFT of input signal which receive from VISA read ?

Hi.
I receive data from MCU whcih sampling frequency is constant and we assumed it is S. now I get data from MCU with using VISA read block. I can display data, perform some functios like filtering, multiply and save them in txt files. all thing is OK.
but when I want to see FFT of incomig data on chart , it doesn't work !! I use this VI for calculate and display FFT of input signal (from VISA read) and display it which in Y-Axis is magnitude and X-Axis is frequency.
in your mind why this is not work and what I must done for show input signal FFT and frequency components ?
Thanks.

If I understood this correctly, you are getting the correct results when outputting to a text file but you are not able to see the results when trying to output to a chart?
This discussion may be of some help to you.
Rob S
Applications Engineer
National Instruments

FFT pour un signal analogique en temps réel

Bonjour,
Je souhaite calculer la FFT d'un signal sortant d'un générateur de fonctions?
Comment je dois le faire sur Labview? J'arrive pas à trouver les bonnes fonctions qui transforment ce signal qui est en temps réel en un signal manipulable par la fonction FFT disponible. sur la palette de fonctions de Labview.
Merci d'avance pour toute remarque, aide ou suggestion.

Greetings Sir,
You can find many examples of the correct use FFT functions inside the LabVIEW Example files. The FFT functions come in two version,the 'default' and the 'point by point'
The links above show the wiring options of each of these functions.
Be aware that these vi's do not come with the LabVIEW Base version, they are available in the LabVIEW Full and onwards.
Kind Regards,
Wouter
Applications Engineering
National Instruments Belgium

HT1515 I'm getting poor performance from my apple TV, will plugging in my airport express via ethernet to apple tv increase its performance (poor wi-fi signal)

I'm getting poor performance from my apple TV, will plugging in my airport express via ethernet to apple tv increase its performance (poor wi-fi signal)

Yes, though it is less ideal than what I suggested earlier. You would need to place your AirPort Express in a location approximately midway between your AirPort Extreme Base Station and the TV. Then, using AirPort Utility, configure it to "extend a wireless network".
It may help. Bear in mind the signal thus "extended" by the Express can only be as good as the signal it can receive from the Extreme. That is the reason for selecting its appoximate midway location.
Read about it here: http://support.apple.com/kb/HT4145
Scroll down to "Wirelessly Extended Network (802.11n)" for a picture.
This solution requires an all-Apple wireless network. No third party stuff.
You mentioned using Ethernet. That would be a better idea. Scroll down to "Roaming Network (Ethernet-connected Wi-Fi base stations)" for a picture. In your case, the longer the Ethernet cable - hence the closer you can move the Express to the TV - the better

Which daq card supports to perform fft operation on complex analog signal

i need to process complex analog waveform for radar based applications.i need a suitable daq card for doing that task.please specify suitable card and application notes to perform dsp based applications.

The answer to your question depends largely on the sample rate, resolution, and number of channels you want to have. The first place I would look is the M Series devices at http://www.ni.com/dataacquisition/mseries.htm. Using LabVIEW, these analog input devices can read in a signal and easily perform an FFT on it.
Michael P
National Instruments

MyRIO FPGA FFT Express VI timing analysis for multiple input mode - trying to perform fft's on a 3-axis accelerometer

Hi Everyone!
Project Background:
I've been working with the myRIO FPGA in an attempt to generate an application capable of sampling a tri-axis accelerometer and performing an fft on each axis. I've successfully developed an application for a single axis, but attempting to duplicate the code to sample the second and third axes in parallel results in an estimated 150% resource utilization for the tiny FPGA's LUT's. Additionally, I'm looking to avoid sequentially processing each accelerometer input using triggers and a single fft block because that reduces my fft update frequency significantly (e.g. I can't calculate another fft for input 1 until I calculate an fft for inputs 2 and 3).
After reading up on the fft vi, I'm thinking that I can use the M-interval input indexes / Continuous output indexes Input/Output Index Pattern mode. My thought is that I can edit the vi to remove any math that "recombines" these three vectors into a single fft, resulting in 3 separate fft's. I'm also hoping that this process requires less time than using the sequential method described above.
The Questions:
1. Has anyone done an fft on three inputs using the myRIO at sampling rates > 20kHz and fft sizes of 1024 or larger? If so, I may just be lacking some proper resource management.
2. Does anyone know where to find timing information on the M-interval input indexes / Continuous output indexes Input/Output Index Pattern mode? The manual only provides timing diagrams for singel channel / single input modes. I don't want to waste my time modifying the vi if it will still take 3x as long (assuming modifying the vi is even a possibility).
Further Information:
I already have an application written that samples the accelerometers at >20kHz and then performs the fft on the main processor, but now I'm looking to see if it is possible to perform all signal processing on the FPGA side. The processor performs decently enough, but the timing is not as consistent as I would like it to be. Lastly, I am aware that the myRIO itself has a built in accelerometer, but I need to mount the accelerometer in an environment where the myRIO would probably be damaged and definitely cannot fit.
Any thoughts are much appreciated! The excessive FPGA compile times for this thing make the old guess and check method less appealing.
-Chris

Hi Chris,
Thanks for posting and the detailed background on the project! To answer some of your questions:
1. The FFT Express VI does use a significant amount of space. The FPGA on the myRIO is somewhat limited space-wise. Your best option may to implement the FFT for 1 channel on the FPGA and the other two on the RT side.
2. I converted the FFT Express VI to a subVI and I am not sure if you can trim too much code from it. The subVI is also very complex so re-working it would be a significant amount of work. I could not find much documentation on M-interval input indexes / Continuous output indexes Input/Output Index Pattern mode timing.
I hope that this helps!
Thanks,
Frank
Application Engineer
National Instruments

How to do FFT of vibrations signal?

Hello,
I'm trying to measure the time and frequency spectrum of a vibrations signal.
My time plot seems to be ok, but my FFT graph doesn't look right.
An expected vibration FFT graph of a bearing should look like peaks at various frequencies, but my FFT graph looks only like a linear line.
Does anyone know what's wrong with my attached program?
Thank you.
Y.Yang
Attachments:
3 axis white and green sensors v2.vi ‏122 KB

Your code looks fine. I double checked how you're acquiring data, and it seems fine. I'm pretty sure that you are acquiring an FFT and the graph is just not scaled correctly. Do the following:
Right Click Waveform Graph 2 >> X Scale >> AutoScale X
Right Click Waveform Graph 2 >> Y Scale >> AutoScale Y
I've also attached an example of what I've done to get the FFT from a simulated signal.
Che T.
Applications Engineer
National Instruments
Attachments:
FFT.vi ‏67 KB
fft.png ‏43 KB

FFT d'un signal

Bonjour
J'ai réalisé une application qui échantillonne des signaux à 5kHz (avec une carte NIUSB6210).
Je souhaite garder uniquement le signal à 50Hz de ces signaux (avec une FFT) et avoir la courbe à 50 Hz.
Est ce que ce traitement et possible?
Si oui comment?
Merci
Cordialement
Damien

Bonjour,
Merci d'avoir posté votre question sur le forum de national instruments.
Ce traitement est possible, il vous fait consulter l'aide labVIEW et aller dans recherche d'exemples. Il vous faut utiliser un passe bande en choississant le bonne ordre etc...
J'ai trouvé un VI sur la FFT. Vous pouvez le consulter et prendre exemple.
Brice S.
National Instruments France
Pièces jointes :
Frequency Analysis of a Filter Design - DFD.vi ‏32 KB

I need use the line data(basler spl2048 camera,NI1433 board) to perform FFT transform ,how can i use transformed data to construct an image

hello everyone! as what i haved mentioned in the title.In optical coherence tomography system ,i need to perform for every line data whick accquired by NI1433,how can i use
the transformed data tto construct an depth image .

This is no longer my main area of expertise, but here is results of brief search:
Spectral Domain Optical Coherence Tomography System Design: sensitivity fall-off and processing speed enhancement
look at Chapter 5
https://circle.ubc.ca/bitstream/id/91474/ubc_2010_fall_chan_kenny.pdf
Ultrahigh-resolution, high-speed, Fourier
domain optical coherence tomography and
methods for dispersion compensation
http://www.opticsinfobase.org/oe/abstract.cfm?uri=OE-12-11-2404
hope this helps,
Curt
Curt Corum, Ph.D.
Center for Magnetic Resonance Research
University of Minnesota

FFT avec un signal d'entrée variable

hello to all
who has an idea how I can change the input FFT Example (windowed FFT) which in underneath the tree Labview 2011
see Figure telque entry that I would change is cerculer black
Pièces jointes :
pa.jpg ‏346 KB

Hello basmasag,
I'm not sure what you want to do, but you can modify this part of the diagram with some E/S from modules installed on your target for example.
You can put instead of 'sine wave generator', 'square wave generator' for example too.
I hope it's help you.
Regards,
Jérôme Henrion | NIF - Application Engineer | PXI Captain
Certified LabVIEW Developer

Apply FFT on recording signal

Hi,
since the ios 4 we can take advantage of the accelerate framework which holds the vDSP API and this has a FFT in it. I want to use that for the microphone input and filter low tones with a low pass filter. can somebody explain me how to apply the FFT to my microphone input and then deal with the data from the FFT or does somebody has a link for me explaining that?
would really appreciate that, thx.
palmdale

I dont think I more info about this. Try googling yor way around or try looking into the free books apple has provided for developers. You might find something in these books.
http://www.tuaw.com/2010/12/19/apple-posts-free-developer-documentation-for-iboo ks-users/

Perform Hamming window and FFT with Java

Hi all,
I am trying to apply Hamming window on my lengthy sound data soundSample[1000] with window length 100. Then proceed with FFT.
And i found that java does have the package for Hamming window and FFT. As below,
http://code.compartmental.net/minim/javadoc/ddf/minim/analysis/FFT.html
http://marf.sourceforge.net/api/marf/math/Algorithms.Hamming.html
But i hardly find an example that illustrate how to use the package in a java program. So no idea how should i use the method in package.
Please advise and appreciate if reference is provided.
Thank you.

Hi,
I have spent sometimes to study and do the coding for FFT on audio samples.
My project is to study the FFT working by performing the FFT on audio sampled data.
After this is done, then only proceed to extract the pitch value in the audio data.
Below is the coding that i have done by referring to the provided steps:
In my main, i call this method and past the retrieved sampled sound data to this method.
public static void Analyze(int[] soundSample,float sample_rate ) {
        int N = (int)sample_rate/5;
        int Number_Sample = soundSample.length;
        Complex[] fftBuffer = new Complex [2*N];
        Complex[] fftResult = new Complex [2*N];
        Complex [] lastN = new Complex [N];   // The array to save the last N sample
        int delay = 0;
        double delta = 2*Math.PI/(2*N);
        // I have no idea how can i convert my sample array to double so that it will be in the range of [-1,+1]
        while(delay <=soundSample.length){
            //Extract the 2N sample for FFT analysis and convert the data to complex number.
            for (int z=0; z<2*N; z++){
                fftBuffer[z] = new Complex(soundSample[z+delay],0) ;
            for (int i=N-1;i>=N/2; i-- ){
                lastN[N-1-i] = fftBuffer;
for (int z=0; z<2*N; z++){
fftBuffer[z] = fftBuffer[z].times(0.54-0.46*Math.cos(z*delta));
fftResult = FFT1.fft(fftBuffer);
delay = 2*N + delay;
1) I was trying to perform FFT with 2N samples then keep on looping the FFT method until 2N reaches the ends of sampled data.
But the FFT that i am working with is radix 2... It doesn't work with my 2N samples... Please teach me how should i work out FFT regardless the number of sample?
2) The hamming window coefficient i m using is based on http://www.mathworks.com/help/toolbox/signal/hamming.html . I am working on index [0:2N] ..
Is it appropriate?
3) According to your No1 steps, the acceptable frequency resolution is 5Hz. May i know what is this representing? And is it application for most of the FFT application? How can i determine the frequency resolution that i should used in my project?
Sorry for late reply as i was trying to work out the thing..
Hereby attach to your the my coding.. and hopes to have your guidance and tutorial how to extract the pitch for recording audio file with Java.
I have done the pitch extraction with MATLAB.. but Matlab as built-in FFT function...
So i m now get stucked how to perform FFT on audio sound sample regardless the N value of sound sample for FFT buffer.
Many thanks for your former advise... and
Looking forward for your replies again.
Happy New Year 2011 :)
Edited by: 诸葛 on Dec 31, 2010 9:29 AM

Frequency Response VS FFT for measring frequency response of a audio ouput signal.

We have purchased the Sound and Vibration Toolkit and I have some questions.
From the frequency response example I looked at you measure the input then the ouput and the Vi gives you the difference.
I want to measure the audio frequency response a radio.
So all I have is the output I dont have the audio input to use as a reference.
How would I measure frequency response with the frequency rasponse VI with only the output audio signal?
I was also looking at the FFT example to measure the audio signal frequency response.
But from what I can tell so far this only does 1 channel I want to do both channles at the same time.
Is there a way to do FFT on 2 channels at once and have them output on the same graph?
Thanks for any help you can provide.

Hi,
I was looking through the examples and If you look at the SVXMPL_Multichannel FFT (simulated) examples, this shows how to take an FFT with multiple signals. You just pass in an array of the waveforms. If you need to put your signals together you can use the merge signals VI, which is located in the Express»SignalManipulation Pallette. Let me know if you need any further help with this issue.
Have a great day,
Michael D
Applications Engineering
National Instruments

How to measure/estimate Bias of the signal

Dear Sir
I am performing the FFT of the signal which collect in real time from the hall effect current tranceducer SCT-013-005. I need to measure/estimate bias of this signal. Can you please guide me how can I do that. (Attached is my vi which is developed in LabVIEW 2012)
I shall be thankful to you for your attention and consideration.
Kind Regards
Urfee
Solved!
Go to Solution.
Attachments:
How to measure Biase of the signal.vi ‏930 KB

Hi tronoh,
what about using the "Basic Averaged DC&RMS" function on your periodic signal?
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome

What is the output on the FFT PSD function?

I am trying to evaluate the FFT PSD function relative to frequency. I expect f(0) = the variance of all signals, but that is not what is given. Does anyone have any information about this. I ran a test array with a 1 Hz sin wave, with 10 samples/second, 120 total data points--the FFT PSD gives f(0)=0.

Hi,
The LabVIEW help file gives the following information concerning this function:
The FFT Power Spectral Density VI completes the following steps to compute power spectral density.
Computes the FFT of time signal.
Forms the power spectral density of time signal.
Averages the current power spectral density with the power spectral densities computed by the VI since the last time the averaging process was restarted.
Returns the averaged power spectral density in power spectral density
The single-channel version of this VI can perform single-channel measurements in both one-shot mode, meaning a single call, and continuous mode, meaning multiple calls with history. The single-channel version can perform multichannel measurements only in one-shot mode. If you want to make multichannel measurements in continuous mode, use the multichannel version of this VI.
The single-channel version of this VI maintains internal state information for a single channel only. Calling the single-channel version to process another channel without using the restart averaging control to clear the history results in an unexpected behavior of this VI. The unexpected behavior results from the VI passing the internal state information from one channel to another.
Note The single-channel version of this VI is primarily intended for continuous processing of a single channel. Do not generalize this behavior to the multichannel case and use the single-channel version in a For Loop to continuously process multiple channels by indexing an array of waveforms. Refer to the examples\measure\maxmpl.llb and the examples\analysis\measxmpl.llb for examples of how to use a multichannel version of a VI like the FFT Power Spectral Density VI in a loop.
Refer to the Noise Waveforms and PS Density VI in the labview\examples\measure\maxmpl.llb for an example of using the FFT Power Spectral Density VI.
Amanda Howard
Americas Services and Support Recruiting Manager
National Instruments

Perform FFT on stationary signal

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