Find all peaks in FFT spectrum

[Konvict]

Hello,

I am reading data from a text column and doing FFT. After FFT I would like to get ALL frequencies which are above a specified threshold. I am already using peak detector but I only get 1 value as a result. But I would like to get all frequencies which are above the threshold. I attached a screen.

In short, how can I use the peak detector function to get multiple peaks from FFT data, instead of just one (which is always the first one above the threshold).

Thanks

[wiebe@CARYA]

>After FFT I would like to get ALL frequencies which are above a specified threshold.

This is in contradiction with your title. The title says you want all peaks, here you're saying you want all frequencies above a maximum. This is a totally different problem.

I'm not being picky here, peak detection is tricky and starts with a good definition of the what you require.

>I am already using peak detector but I only get 1 value as a result. But I would like to get all frequencies which are above the threshold. I attached a screen.

To get all frequencies above a threshold, simply do a compare (x>y) between the frequencies and the threshold. You'll get an array of Booleans. Put them through a for loop, and output the loop counter as a conditional array. Then you'll have all the frequency indices above the threshold.

In short, how can I use the peak detector function to get multiple peaks from FFT data, instead of just one (which is always the first one above the threshold).

Try (NI_AAL_SigProc.lvlib) Peak Detector.vi (quick drop: "Peak"). 

[cstorey · Accepted solution]

I posted a peak detection snippet last week that might be useful..

https://forums.ni.com/t5/LabVIEW/How-to-find-the-Nth-lowest-local-maximum/m-p/3686345#M1036545