STFT Spectrogram - 50% Overlap

[dan07]

Hello everybody...

I have a array with 1024 points and from it I've created a waveform with DT 0.1.

I need to perform a STFT Spectrogram analysis using overlapped segments of 512 points.

Segment number ONE will go from point 0 until point 512

Segment TWO will go from point 256 until point 768

Segment THREE will go from point 512 until 1024

I don't know how to set up the STFT Spectrogram VI to obtain this kind of analysis. Example file it is attached.

Thanks in advance for any kind of help.

 Dan07

[tinnitus]

hello Dan,

i have made some modifications to make your vi little bit more flexible,
 so you can define other windows sizes and overlap .
i place a log fct just to compress data and make them more visible when displayed.

i let your data to waveform but i don't think there is an interest , it's up to you...
window size is defined by bitsize so if you want 512 type 9 same with oversize

time block is just here to let you see the stages...

@+

Tinnitus

[dan07]

Hello

My Labview version it's older than yours. Please save to 8.5.

Thanks

Dan07 

[tinnitus]

my post is upside down,  i don't why (i am using opera ????) 

@+ Tinnitus

best regards

Hello, idon't have labview on the computer i 'm actually using, but i have posted vi in jpeg format...

[tinnitus]

hello,

sorry for delay, here in 8.5

@+

Tinnitus

[dan07]

 Hello...

I understood what you made. You fed the for loop always with the whole series but use each iteraction to split a segment from the whole series, and each segment had been analyzed by STFT. I've created a array to view the values and I am a little bit confusing about the results.

Since that I am using segments with 512 points overlapped by 50 %, and my whole series have 1024, I was expecting to get a array with 3 columns (each column with the result of spectral analysis for each segment), and each column would have 256 values, because a segment of 512 points processed by spectral analysis will generate "length of segment/2" number of points. But I got a big array with so many columns and rows, do you know why?

Find attached the modified version.

Thanks for attention

Dan07

Message Edited by dan07 on 01-26-2009 12:14 PM

[tinnitus]

hello,

May be you mix with FFT if you want 3 array of 1D use FFT

SFFT is a  spectogramme function (time-frequency ) so result is in 2D     f |_ t

what is the aim of your project ?

to create a spectogramme using FFT ?

@+

Tinnitus

[dan07]

Hello

The aim of my project its to take a signal and calculate the power spectral density of it. The signal will be interpolated by cubic spline, and the interpolated series will be splitted in segments of 512 points overlaped by 50 %. Each one of these segments will have the PSD calculated. The STFT results are the same that the results obtained by PSD?

Thanks

Dan07

[tinnitus]

---

dan07 a écrit:

Hello

 The STFT results are the same that the results obtained by PSD?

Thanks

Dan07

---

no...

[tinnitus]

here the same with psd