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Store FFT traces?

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Store FFT traces?

Postby TeeBee » Thu Jul 07, 2016 2:14 pm


Hopefully I'm just being dumb and overlooking something but I can't figure out how to a particular job -- trying to get (audio) frequency response plots from the FFT. I've got it set up now so that I can get decent plots, but would like to be able to 'capture' the current plot and then superimpose further plots so I can build up an image of how changing a particular control on the EQ alters the Freq-response.

I am using a 3206B unit with PicoScope 6 software.

I have the software in FFT mode, 50kHz bandwidth.
Signal generator producing White Noise.

Spectrum Bins 16k (though I have played around with this), Blackman capture.
Y axis - Set to Average, Log, dBu
X axis - log10, 4 decades

I tried the reference waveforms though if I save one it doesn't appear to be doing the averaging.

Pretty new to this so a distinct possibility I'm missing an obvious!
Thanks, Tom
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Re: Store FFT traces?

Postby Gerry » Wed Jul 13, 2016 10:45 am

Hi Tom,

You can do averaging in the frequency domain (If you go to 'FFT options', i.e. the icon next to the Spectrum Mode icon with the spectrum and arrow image, and under the 'Y-axis Display Mode', in the drop down list select 'Average') but it won't keep traces on the screen, it will replace traces with just one average trace.

What you are trying to do is get a persistence plot (where the waveforms are not replaced and instead build up a composite image over time) in the frequency domain. We only have persistence in the time domain (which is the icon next to the spectrum mode icon on the other side). However, to be able to clearly see how the frequency response changes, what I believe you really need is not persistence, but 3 parameters plotted at once, i.e. frequency, amplitude, and time which, to be able to see at once, requires a 3D plotting tool.

We don't have a 3D plotting tool in PicoScope 6, but if you are able to develop an application with Matlab you could perform 3D plots using that environment. You could download our Software Development Kit from the downloads page on our website to get the driver you need, along with some example code to get you started. However, I'm guessing that you probably need some time to familiarise yourself with PicoScopes before tackling something like that. In the short term you could ask on the forum if anyone has a 3D FFT plot example that you can use.


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