2
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Why do DFT frequency buckets need to be divided by sample period?
I might be late to this question but the problem with frequency bins isn't about normalization. After your FFT, each frequency bin is calculated as
$$ f_k = \frac{k}{N} \cdot f_\mathrm{s} $$
where $f_\...
- 159
2
votes
2
votes
Accepted
Welch method implementation not smooth
myamps = (abs(np.mean(complexData_list,axis=0))**2)
Looks like the order of operation here is wrong. You should FIRST calculate the magnitude squared and then take the mean. The PSD is the average of ...
- 42.7k
1
vote
Accepted
Scaling plots after FFT
Your professor, just like your last question, seems to be providing you with erroneous prompts.
His plot shows $\tt{dB}$ values on the y-axis of the FFT plot, but these are actually linear.
With that ...
- 5,247
1
vote
Is this FIR filter considered symmetric?
Sometimes you need to go back to high-school algebra (assuming you had a good math program in high school).
The answer to "Is $f(n)$ symmetric?" is shorthand for "Is $f(n)$ symmetric ...
- 11.9k
1
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Calculate Total Harmonic Distortion (THD) from FFT Plot
The output of a single-sided DFT such as this is scaled by the number of samples. Therefore, for an input time history that is $N$ samples in length, the DFT at each frequency point returns the ...
- 11
1
vote
Accepted
Characteristics of linear systems in the time and frequency domain
The problem with the third way of doing things is that there is time-domain aliasing happening. To avoid time-domain aliasing using this method, the length of the FFT needs to be
$$ N_{\tt fft} = N_{\...
1
vote
Accepted
How to calculate a 3D Fourier Transform?
Do not expect to see anything interesting in the Fourier transform spectra, whether 3D or 1D spectra, of forced oscillations with resonant frequency. Any natural oscillations that may (and should) ...
- 1,694
1
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Physical interpretation of frequency domain data of signal noise
The Fourier transformation attempts to imitate a signal using a selectable number of sin and cos functions. Since the sin/cos functions for $t \to\pm\infty$ do not disappear asymptotically, the signal ...
- 21
1
vote
Accepted
Physical interpretation of frequency domain data of signal noise
The results of the Fourier Transform(s) generally produce a "spectral density". For the Discrete Fourier Transform the spectrum has the same units as the original signal, i.e. Volts in your ...
- 42.7k
1
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Physical interpretation of frequency domain data of signal noise
Compute the magnitude:
$$|X_f| = \sqrt{(\Re(X_f))^2 + (\Im(X_f))^2}$$
Depending on the scaling used by your FFT routine, you might have to scale the result by the length of your FFT.
I suggest you try ...
- 5,247
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