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rush3k
Joined: 31 Mar 2006
Posts: 36
Helped: 8
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 01 Mar 2008 20:16 Need your DSP/FFT expertise |
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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?
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supiper
Joined: 26 Jan 2007
Posts: 226
Helped: 112
Location: TUNISIA
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| 02 Mar 2008 21:16 Re: Need your DSP/FFT expertise |
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| 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.
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rush3k
Joined: 31 Mar 2006
Posts: 36
Helped: 8
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| 02 Mar 2008 21:26 Re: Need your DSP/FFT expertise |
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| supiper wrote: |
| 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.
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supiper
Joined: 26 Jan 2007
Posts: 226
Helped: 112
Location: TUNISIA
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| 03 Mar 2008 13:54 Re: Need your DSP/FFT expertise |
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| rush3k wrote: |
| supiper wrote: |
| 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:
http://en.wikipedia.org/wiki/Bode_plot#Gain_margin_and_phase_margin
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khubaibahmed
Joined: 24 Aug 2005
Posts: 32
Helped: 2
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| 27 Mar 2008 10:47 Re: Need your DSP/FFT expertise |
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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)) [/tex]
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calm
Joined: 17 Oct 2005
Posts: 271
Helped: 5
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| 02 Apr 2008 4:21 Need your DSP/FFT expertise |
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| the diagrams is confuse me
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