Finding maximum peak values and how to change x_axis to frequency and y_axis to gain

[Arbo]

HI i have a VI file, that takes wav file and converts it to spectrum . i need to find all maximum peaks by treshold (-30) level. I found couple of examples but i can not understand why it displays wrong data at my vi, may be i'm doing something wrong?  and another issue , how to display the right x-axis with frequency and gain in y_axis. i know that formula for x_axis is 

bin num * sample rate(8000)/framesize (???) which framesize i need to take?

and must to enter this value to scale multiply in the property window. this vi after compilation to dll, will be used in my C# project.

i have attached the vi , and wav file two tones 2KHz and 4KHz.

[James.M]

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@Arbo wrote:

HI i have a VI file, that takes wav file and converts it to spectrum . i need to find all maximum peaks by treshold (-30) level. I found couple of examples but i can not understand why it displays wrong data at my vi, may be i'm doing something wrong?  

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Why do you have a For loop iterating through the same data..? By default you have a zero wired to the N input on the loop, so you won't get any values out. Either get rid of the loop, or set a value of 1 instead of 0.

What do you mean by wrong data? What is it supposed to be and what are you getting?

[Arbo]

Thanks for an answer i have settled the N=1 and attached the graph view, the Gain displays the right value but frequency has a value of 0.006 how i can convert this value to the graph. the signal of wav file has 2 main tones 2Khz and 4Khz, and at spectrum i want to see the these frequencies at right places.

[GerdW · Accepted solution]

Hi Arbo,

do you note the coercion dot at the FFT function input? It has a reason to be shown!

Please read the help for the functions you use in your VI: The FFT function expects a waveform input - waveforms include timing information.

Your data are just a 1D array of samples without any timing information…

Solution: Povide the data for FFT with a waveform including proper timing information!

[Arbo]

thanks, for a help. i resolved this issue with proper timing .

but i have another question how i can insert an marker to the graph as it made in spectrum analizer with peak marker function. 

[GerdW]

Hi Arbo,

graphs support cursors and annotations. You can use both as "markers" in the graph.

There are also example VIs in the LabVIEW example finder explaining how to use both…