Graduate Signal Processing and the Duffing ODE

[member 428835]

Hi PF!

Attached are two plots: signal.pdf is a solution from the Duffing ODE, and plots vertical displacement over time, both the raw signal (blue) and the reconstructed signal from an FFT (red). I've also shown a zoomed in view so you can see how oscillatory the signal is.

pow.pdf plots the FFT, showing one main frequency observed.

My question is, have I correctly reconstructed this signal? Sure look like I've done something terribly wrong, but perhaps I have not?

 

[member 428835]

NVM, I figured it out. Thanks though.

 

[jedishrfu]

So what was it sampling rate wrong?

 

[member 428835]

Yep! Only took me all afternoon to figure it our lol

 

[jedishrfu]

There that's frequency constraint aka the Nyquist frequency that always gets me.

When we first did FFT plots in MATLAB we constructed a dual signal by adding two sine curves and then checking to see that the FFT got the spectrum right.

 

[member 428835]

There that's frequency constraint aka the Nyquist frequency that always gets me.

When we first did FFT plots in MATLAB we constructed a dual signal by adding two sine curves and then checking to see that the FFT got the spectrum right.

That's ultimately how I figured out what was wrong actually...take it back to a pure sine wave and it better be 100% accurate right?