FFT window(buffer) size setting & frequency resolution, configurable

[mechatronics2020]

Hello, 

I am trying to obtain the frequency spectrum of a signal. I am using the "SVAF FFT Spectrum" block in sound and vibration toolkit.

My question is how can I define FFT window size? As far as I understand,the block by default calculated the FFT in a signle window with the size of the input data. Therefore the frequency resolution is equal to 1/(signal duration). In my case:

- Sampling rate is 100.000 Hz,

- Signal duration is 7.5 s,

- Total data samples is 750.000 points.

I want to create a coarser frequency spectrum, therefore I need to decrease the FFT window. However I could not figure how to set the FFT window size.

I would really appreciate your help.

[Henrik_Volkers]

For a coarse FFT display : How many points you need for your indicator window (screen)  .. be generous say 2k points?

so you need double number of wfrm points .. 4k

You say 100kSPS .. dispaly range up to 50kHz?

50k/2k  results to 25 Hz bin  (/pixel) resolution in your display then.

with actual computing power , how about reading it in 4096 sample chucks pipe to saving and display loop . display mean and peak or slow and fast mean ..with 10 to 5 updates per sec?