Overlapping windows for FFT in DasyLab

[VinceR]

Hello,

I understand the purpose of windowing and overlapping windows for FFT calculation and I am trying to visualize it using Dasylab.

I am purposely choosing sample rate, block size and frequency for the generated sine wave so, that the signal is not periodic in one block length and windowing becomes necessary to read the correct frequency and amplitude from the FFT calculation.

My problem is that I am not able to get any change in the windowed signal nor in the FFT results by changing the overlapping parameter. For some reason (and I might be the reason why...) the overlapping does not work.

There is only very limited help or manual content for Dasylab, so I would be thankful if someone has an idea on this forum!

Thank you!

Vince

[DAQman]

Could you add some phase shift to your generated sine wave so it doesn't begin and end at zero? The results should indicate an FFT that spreads out more at the bottom when using NOP for the Window function. 

[VinceR]

On 7/10/2024 at 4:21 PM, VinceR said:

My problem is that I am not able to get any change in the windowed signal nor in the FFT results by changing the overlapping parameter. For some reason (and I might be the reason why...) the overlapping does not work.

Hello and thank you for your answer!

The question I had was regarding the overlapping of the blockwise windowed signal. I am not sure to understand your answer.

Can you show the parameters for both inputs in your Data Windo00?

Thanks

Vincent

[DAQman]

There is no way to see the overlapping because it happens in the FFT module. You don't realize it, but in the background, the Data Window module transfers a block of data sized by the Window function to the FFT module. In doing so, it also specifies the overlapping number.

 

[VinceR]

Thank you!

That's interesting, I would have expected the Window module to work on its own and output the windowed signal.