1k views

Computing Power Spectral Density from FFT vs Welch's method vs Periodogram [duplicate]

I'm looking into different ways to get the Power Spectral Density (PSD) (while toying around with python) of a discrete signal/time series, and I'm struggling to understand why I get (very) different ...
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979 views

How to downsample a fourier transformed signal?

I have a signal of length 100000 timestamps sampled at a frequency of 25kHz. First I apply a high pass filtering at (300Hz) and then do the Fast Fourier Transformation. Then the absolute values are ...
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260 views

Energy and Power: Power Spectral Density is units of Energy

To help focus answers: The following is specific to “Energy” and “Power” as used for signal processing, not physical units of energy and power (then to ask can units of “Watts” and “Joules” be used, ...
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1 vote
901 views

Are there any difference between the FFT magnitude of a signal and average FFT magnitudes of the signal broken into multiple frames?

Suppose I calculate the FFT of a 5 seconds sound wave. If I'm only interested in the FFT magnitudes across frequencies, I should obtain the same result if I segmented the sound wave into five 1-second ...
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194 views

Differences in PSD for windowed vs non-windowed spectra

For a non-windowed spectrum, this article gives this equation for the power spectrum $$\text{PS}(k)=\frac{1}{N^2}|X(k)|^2$$ and this for the power spectrum density \text{PSD}(k)=\frac{N}{f_s}\text{...
1 vote
545 views

SNR of averaging FFT in magnitude

Suppose we record $N$ repetions of a sinusoidal signal with noise (recording $M$ time points). We are interested in the magntiude spectrum. To improve the SNR, I average the signal traces from ...
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1 vote
225 views

Why is the sample spectrum considered inconsistent?

In multiple sources of the literature, e.g. here or here, it is stated that the sample spectrum (i.e. calculating the spectrum of an input signal by simply squaring the magnitude of the DFT) is ...
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1 vote
374 views

Check whether signal is periodic

I have a signal with multiple frequencies. The frequency changes depending on the amount of air flowing through the fuel snap. The signal resembles a square wave ranging from $0.4$ to $4.5$ Volts and ...
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467 views

computing the averge power spectral density with python

In order to compute the power spectral density of a signal, we can use np.fft.ftt in python in the following formula: ...
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