Need your DSP/FFT expertise

[rush3k]

compute cutoff frequency

The pictures are of my FFT. I use it to extract the -3dB frequency. Also use it for the -3db to -6dB rolloff slope, not sure if this of much use yet.

I'm wondering what other ways you guys out there use the FFT. What other information can you glean from the amplitude, magnitude and even phase data?

 

[supiper]

Pictures present Bode plot (and not FFT) of a bypass filter. The frequency that you extracted at -3db presents the cut-off frequency of the filter.

 

[rush3k]

Pictures present Bode plot (and not FFT) of a bypass filter. The frequency that you extracted at -3db presents the cut-off frequency of the filter.

So what information do you get from your Bode plot, that was my question.

 

[supiper]

Pictures present Bode plot (and not FFT) of a bypass filter. The frequency that you extracted at -3db presents the cut-off frequency of the filter.

So what information do you get from your Bode plot, that was my question.

Bode plots are used to assess the stability of negative feedback amplifiers by finding the gain and phase margins of an amplifier, see this link:
https://en.wikipedia.org/wiki/Bode_plot#Gain_margin_and_phase_margin

 

[khubaibahmed]

Dear both are frequency responses. The first one is 20*log|H(ω)| against Frequency (Hz) and second one is normalized by max(20*log|H(ω)|).

If u want to compute cutoff frequency for this system then use normalized one.
Second plot is generated using two arrays say H along y-axis and f along x-axis i.e plot(f,H)

How you can compute -3dB cutoff:

x=find(H<=-3);
Cutoff=f(X(end)) \]

 

[calm]

the diagrams is confuse me